Small-scale water treatment solutions - ULisboa...it came to my mind that the only thing that...

Small-scale water treatment solutions

Ivan Jorge Sokil Rodrigues de Carvalho

Thesis to obtain the Master of Science degree in

Civil Engineering

Supervisor: Professor António Jorge Silva Guerreiro Monteiro

Examination Committee

Chairperson: Professor António Alexandre Trigo Teixeira

Supervisor: Professor António Jorge Silva Guerreiro Monteiro

Members of the committee: Professor Filipa Maria Santos Ferreira

December of 2016

ii

Dedicated to my parents

iv

Acknowledgements

It may be said that this document is the culmination of a 17 year long journey, it is something I began

preparing unaware in primary school. As with any other journey, some rainy days were endured, and

some twisted paths were trekked. Sometimes I cried, sometimes I laughed. Sometimes I felt on my

knees, sometimes I ran. One, sometimes, does not know whether the sum of all these experiences with

diferent polarities will have a positive balance in the end or not. But, in this case, mainly due to the

influence of some persons, I can happily say that the balance was exceptionally positive. These persons

managed to turn the negative experiences a little less negative and the positive ones a little more

positive. Also, the longer they accompanied me for, the higher impact they had in the outcoming balance.

As such, I would firstly like to thank those who have been with me since the beginning, namely, my

parents Jorge and Vera, and my grandparents Seara and Lucinda. Secondly, I also would like to thank

two great friends of mine, Bruno and Devan, who have also supported me through the majority of this

journey. Thirdly, I would also like to thank to all those persons that, although not here mentioned, have

also had a positive impact in my life and are greeted with a smile whenever I see them.

From another point of view, the academic one, I would firstly like to thank Professor António Monteiro,

my supervisor, who, despite not answering my emails, probably by virtue of his hectic lifestyle, was

always available upon request to clarify my doubts and use his extensive professional experience to

help me develop this document. Also, I would like to thank the professors who belong to the Department

of Civil Engineering (DECivil) of the Instituto Superior for their commitment and the quality of the

instruction that they transmit throughout the many courses that they teach. After spending a semester

in the best Chinese university and one of the top ranked universities in the world, Tsinghua University,

it came to my mind that the only thing that separates Instituto Superior Técnico from such an university

is, thankfully, not the quality of the instruction that our professors transmit, but rather the lack of funding.

As such, I would like to incite the professors to keep improving and commiting themselves to instruct

the upcoming generations so that they can graduate knowing that they have all the tools to be able to

conduct a successful carreer and to be as competitive and as competent as other graduates from higher

ranked universities.

vi

Abstract

In recent years, it is known that the investment cost of small scaled water treatment technologies has

been gradually decreasing. However, the extent to which this decrease occurred and the most

economically viable treatment solutions for a small scaled water treatment plant are unknown. In order

to assess this, the raw water treatment requirements were firstly determined through the comparison of

the Portuguese legal framework concerning raw and drinking water quality. Then, the expected

treatment efficiencies of several water treatment unit processes were researched and their costs

estimated using cost models that were based on the Work Breakdown Structure (WBS) models

established by EPA. The treatment scheme solutions were then established and their costs estimated

by choosing the cheapest treatment unit processes whose expected efficiencies would be sufficient to

effectively treat raw water with different levels of quality. It was found that, if the raw water was of a high

quality, a conventional water treatment scheme, consisting of fundamental unit processes such as

filtration and disinfection, was the best choice regardless of the type of water residual treatment chosen.

In case the water was of a low quality, a water treatment scheme consisting of reverse osmosis and

other pre-treatment processes was, in general, the most economical choice. In this case, the

conventional treatment only surpassed the reverse osmosis treatment at higher daily treatment

capacities as a result of its comparatively lower water residual treatment costs. Furthermore, it was also

found out that the costs of several treatment processes, including reverse osmosis, whose costs

decreased fivefold, has decreased substantially in the past three decades. This inevitably leads to the

conclusion that small scale treatment plants are becoming progressively more economically viable and,

as a result, they are becoming the best alternative for water treatment in remote places with relatively

low water demands.

Key words: small scale water treatment systems, WBS model, Portuguese water treatment

legislation, water treatment cost, raw water quality

viii

Resumo

É sabido que, nos últimos anos, o custo de investimento em tecnologias compactas de tratamento de

água tem vindo a diminuir. No entanto, não se conhece a extensão desta redução e quais são as

alternativas mais viáveis do ponto de vista económico. De forma a avaliar estes dois últimos pontos,

determinaram-se, em primeiro lugar, as eficiências de tratamento requiridas para a água bruta através

da comparação dos documentos constantes da legislação portuguesa referentes à qualidade da água

bruta e a qualidade da água destinada para consumo humano. Pesquisaram-se, de seguida, as

eficiências de remoção de poluentes de diversos processos unitários de tratamento de água e

estimaram-se os seus respectivos custos utilizando modelos de custo baseados nos modelos Work

Breakdown Structure (WBS) desenvolvidos pela EPA. Posteriormente, estabeleceram-se esquemas de

tratamento com base nos tratamentos unitários mais económicos e cujas eficiências de remoção seriam

suficientes para tratar água bruta com diferentes níveis de qualidade. Verificou-se que, caso a água

fosse de qualidade elevada, um tratamento convencional, constituido por processos fundamentais

como a filtração e a desinfeção, seria a melhor escolha independentemente do tipo de tratamento

residual escolhido. No caso de a água ser de uma qualidade reduzida, verificou-se que um tratamento

constituido por osmose inversa e outros processos de pré-tratamento era, de forma geral, a alternativa

mais económica. Neste caso, verificou-se que o tratamento convencional apenas era mais económico

para valores superiores de caudais diários de água tratada como resultado dos seus menores custos

de tratamento de residuos. Por outro lado, constatou-se que os custos de diversos processos de

tratamento, incluindo a osmose inversa, diminuiram substancialmente nas últimas três decadas. Este

último facto leva inevitavelmente à conclusão que as soluções compactas de tratamento de água estão

a tornar-se progressivamente mais viáveis e, como resultado, são soluções a ter em conta em lugares

remotos com consumos de água relativamente reduzidos.

Palavras chave: soluções compactas de tratamento de água, modelo WBS, legislação portuguesa do

tratamento de água, custo de tratamento de água, qualidade da água bruta

x

Index

1 Introduction ...................................................................................................................................... 1

1.1 Water quality problem .............................................................................................................. 1

1.2 Motivation and goals ................................................................................................................ 2

1.3 Thesis’s structure .................................................................................................................... 2

2 Water quality .................................................................................................................................... 3

2.1 Water quality parameters ........................................................................................................ 3

2.2 Portuguese legal framework for drinking water treatment ....................................................... 4

2.2.1 Raw water classification system ...................................................................................... 4

2.2.2 Water quality required for human consumption ............................................................... 5

2.3 Raw water treatment efficiency requirements ......................................................................... 5

2.4 Raw water characterization according to its origin .................................................................. 7

3 Water treatment unit process cost analysis model .......................................................................... 9

3.1 General overview ..................................................................................................................... 9

3.2 Direct capital cost .................................................................................................................. 10

3.3 Indirect capital cost ................................................................................................................ 13

3.4 Annual O&M cost ................................................................................................................... 16

3.5 Add-on cost............................................................................................................................ 18

3.6 Total annualized cost ............................................................................................................. 19

3.7 Other assumptions ................................................................................................................ 19

4 Cost analysis of unit treatment processes ..................................................................................... 20

4.1 Aeration ................................................................................................................................. 20

4.1.1 Packed tower aeration ................................................................................................... 20

4.1.2 Diffused aeration............................................................................................................ 22

4.2 Adsorption .............................................................................................................................. 22

4.3 Coagulation............................................................................................................................ 25

4.4 Disinfection ............................................................................................................................ 26

4.4.1 Brief introduction and assumptions ............................................................................... 26

xi

4.4.2 Chlorination .................................................................................................................... 26

4.4.2.1 Reaction, feeding methods and inactivation efficiency ............................................. 26

4.4.2.2 Gaseous chlorine ....................................................................................................... 27

4.4.2.3 Calcium hypochlorite tablets ...................................................................................... 28

4.4.2.4 Sodium hypochlorite solution ..................................................................................... 28

4.4.3 Chloride dioxide ............................................................................................................. 29

4.4.4 Chloramination............................................................................................................... 30

4.4.5 Ozonization .................................................................................................................... 34

4.4.6 Ultraviolet disinfection .................................................................................................... 35

4.5 Water stabilization ................................................................................................................. 37

4.6 Filtration ................................................................................................................................. 38

4.6.1 Rapid sand pressure filtration ........................................................................................ 38

4.6.2 Slow sand filtration......................................................................................................... 39

4.6.3 Diatomaceous earth filtration ......................................................................................... 40

4.6.4 Bag and cartridge filtration ............................................................................................. 41

4.6.5 Membrane filtration ........................................................................................................ 43

4.7 Ion exchange ......................................................................................................................... 44

4.7.1 Brief introduction ............................................................................................................ 44

4.7.2 Cation exchange ............................................................................................................ 45

4.7.3 Anion exchange ............................................................................................................. 47

4.8 Membrane separation ............................................................................................................ 48

4.9 Oxidation ................................................................................................................................ 49

5 Water treatment residuals management cost analysis ................................................................. 52

5.1 Process residuals generated ................................................................................................. 52

5.2 Process residual disposal methods ....................................................................................... 54

5.2.1 Off-site disposal ............................................................................................................. 54

5.2.2 Direct discharge to surface water .................................................................................. 55

5.2.3 Discharge to a publicly owned treatment works ............................................................ 55

5.2.4 Evaporation ponds ......................................................................................................... 56

5.2.5 Holding tanks ................................................................................................................. 57

5.2.6 Septic systems ............................................................................................................... 58

xii

6 Treatment schemes definition and cost analysis ........................................................................... 60

6.1 Treatment schemes definition ............................................................................................... 60

6.2 Cost analysis assumptions .................................................................................................... 65

7 Results and discussion .................................................................................................................. 68

8 Conclusions ................................................................................................................................... 76

References ............................................................................................................................................ 77

Appendix A – Thesis defense slides and commentary ......................................................................... 82

xiii

Figure index

Figure 3.1 – WBS model structure .......................................................................................................... 9

Figure 4.1 – Chloramine formation as a function of 𝐶𝐿2:𝑁𝐻4 ratio for a pH between 6.5 and 8 .......... 32

Figure 4.2 – Bacterial growth according to the 𝑁𝐻2𝐶𝑙 concentration ................................................... 32

Figure 4.3 – Particle size distribution of common contaminants and associated filtration technology . 42

Figure 4.4 – Sulfonic acid resin operating capacity vs. regenerant level for sodium-cycle operation ... 46

xiv

Table index

Table 2.1 – Range of values of surface raw water parameters according to each water quality class .. 4

Table 2.2 – Treated water required parametric values ........................................................................... 5

Table 2.3 – Parameter range values and treatment efficiency requirements. ........................................ 7

Table 2.4 – Water class range according to its origin ............................................................................. 8

Table 3.1 - System instrumentation assumptions ................................................................................. 11

Table 3.2 – Fully automated system control design assumptions ........................................................ 12

Table 3.3 – Indirect capital item costs as a percentage of total direct capital costs ............................. 13

Table 3.4 – WBS default complexity factors by technology .................................................................. 14

Table 3.5 – Cost of performance bonds ................................................................................................ 15

Table 3.6 – Cost of the geotechnical investigation ................................................................................ 16

Table 3.7 – Operator labor assumptions ............................................................................................... 17

Table 3.8 – Values assumed for the ventilation energy equation variables .......................................... 18

Table 4.1 – Henry’s constants of the VOCs considered in the analysis ............................................... 21

Table 4.2 – Estimated cost range for a PTA system as a function of treatment capacity ..................... 21

Table 4.3 – Estimated cost range for a diffused aeration system as a function of treatment capacity . 22

Table 4.4 – Reported Freundlich isotherm 𝐾 and 𝑛 values of the VOCs considered in the cost

estimation .............................................................................................................................................. 24

Table 4.5 – Estimated cost range for a GAC adsorption system as a function of treatment capacity .. 24

Table 4.6 – Estimated cost for an activated alumina adsorption system as a function of treatment

capacity.................................................................................................................................................. 25

Table 4.7 – Estimated cost for a coagulation water treatment system as a function of the type of

coagulant used and treatment capacity ................................................................................................. 26

Table 4.8 – Summary of free chlorine CT value ranges for 99% inactivation of various microorganisms

at 5 ºC and a pH value between 6 and 7 ............................................................................................... 27

Table 4.9 – Estimated costs for a gaseous chlorine system as a function of the treatment capacity for

different chlorine dosage ....................................................................................................................... 28

Table 4.10 – Estimated costs for a calcium hypochlorite tablets as a function of the treatment capacity

............................................................................................................................................................... 28

Table 4.11 – Estimated costs for a calcium hypochlorite solution system as a function of the treatment

capacity.................................................................................................................................................. 29

Table 4.12 – Summary of chlorine dioxide CT value ranges for 99% inactivation of various

microorganisms at 5 ºC and a pH value between 6 and 7 .................................................................... 30

Table 4.13 – Estimated costs for a chlorine dioxide system as a function of the treatment capacity ... 30

Table 4.14 – Percentage of hypochlorous acid in free chlorine as a function of pH ............................. 31

Table 4.15 – Estimated costs for a gaseous chlorine feed chloramination system as a function of

treatment capacity ................................................................................................................................. 34

xv

Table 4.16 – Summary of ozone CT value ranges for 99% inactivation of various microorganisms at 5

ºC and a pH between 6 and 7 ............................................................................................................... 35

Table 4.17 – Estimated costs for an ozone generator system as a function of treatment capacity ...... 35

Table 4.18 – UV dosage required for different disinfection efficiencies of pathogenic bacteria ........... 36

Table 4.19 – Estimated costs for an UV disinfection system as a function of treatment capacity ........ 36

Table 4.20 – Estimated costs for a water stabilization system as a function of treatment capacity ..... 37

Table 4.21 – Estimated costs for a rapid sand pressure filtration system as a function of treatment

capacity.................................................................................................................................................. 39

Table 4.22 – Typical treatment performance of conventional slow sand filters .................................... 39

Table 4.23 – Slow filtration system design assumptions ....................................................................... 40

Table 4.24 – Estimated costs for a slow sand filtration system cost as a function of treatment capacity

............................................................................................................................................................... 40

Table 4.25 – Estimated costs of a DE filtration system as a function of the treatment capacity ........... 41

Table 4.26 – Estimated costs for a bag and cartridge systems as a function of treatment capacity .... 43

Table 4.27 – Estimated costs for both micro and ultrafiltration system as a function of treatment

capacity.................................................................................................................................................. 44

Table 4.28 – Estimated costs for a cation exchange systems as a function of treatment capacity for

different hardness concentrations ......................................................................................................... 47

Table 4.29 – Estimated costs for an anion exchange systems as a function of treatment capacity for

arsenate and different nitrate concentration .......................................................................................... 48

Table 4.30 – Estimated costs for both NF and RO filtration systems as a function of treatment capacity

............................................................................................................................................................... 49

Table 4.31 – Doses required according to each oxidizing agent for the reduction of As(III), Fe(II) and

Mn(II) ..................................................................................................................................................... 50

Table 4.32 – Estimated costs of different alternatives for the oxidation process as a function of

treatment capacity ................................................................................................................................. 51

Table 5.1 –Treatment technologies and residuals generated ............................................................... 52

Table 5.2 – NPDES permit costs according to flow discharge .............................................................. 55

Table 5.3 – Estimated costs for an evaporation pond as a function of treatment capacity for different

values of residuals generated ............................................................................................................... 57

Table 5.4 – Estimated costs for a holding tank as a function of treatment capacity for different types of

flow ........................................................................................................................................................ 58

Table 5.5 – Estimated costs for a septic tank as a function of treatment capacity for different values of

residuals generated ............................................................................................................................... 59

Table 6.1 – Average removal efficiencies required ............................................................................... 60

Table 6.2 – Treatment solutions for pathogenic microorganisms ......................................................... 61

Table 6.3 - Treatment solutions for heavy metals and inorganic substances ....................................... 63

Table 6.4 – Treatment solutions for volatile and non-volatile synthetic organic substances ................ 64

Table 6.5 – General cost analysis assumptions .................................................................................... 66

Table 6.6 - Water treatment scheme matrix .......................................................................................... 67

xvi

Table 7.1 – Highest values for the estimated costs in €/m3 for the alternative 1 treatment scheme .... 72

Table 7.2 – Cost breakdown in €/m3 of the A(1,1,1), A(2,2,2), and A(3,3,3) cells of Table 7.1 ............ 73

Table 7.3 – Cost breakdown in €/m3 of the residual treatment solutions according to processes

included in the treatment alternative 1 .................................................................................................. 74

Table 7.4 – Cost breakdown in euros of treatment alternative 2 and its residual treatment solutions.. 75

xviii

Acronyms

AA Activated alumina

AAC Actualized annual costs

CT Contact time

DE Diatomaceous earth

EBCT Empty bed contact time

EPA United States Environmental Protection Agency

FAC Free available chlorine

GAC Granular activated carbon

HT Holding tank

IX Ion exchange

MSBA Multi-staged bubble aeration

NF Nanofiltration

O&M Operation and maintenance

POTW Public owned treatment work

PTA Packed tower aeration

PVC Polyvinyl chloride

RO Reverse osmosis

RSF Rapid sand filtration

TSS Total suspended solids

UF Ultrafiltration

UV Ultraviolet

VOC Volatile organic compound

WBS Work Breakdown Structure

WHO World Health Organization

1

1 Introduction

1.1 Water quality problem

Water is a fundamental resource to all kinds of life forms. Our planet has a hefty amount of water but

only about 2.5% of the water existent is actually drinkable unsalted water (Shiklomanov, 1993). If it is

taken into account that 98.9% of this water is either frozen in glaciers or trapped underground, it is

possible to conclude that only a small portion of water, which in most cases is not even potable, is

actually available for human consumption. From this perspective, it is clear that one of the most

important global challenges resides in the improvement of water treatment systems so that the future

social and economic development of communities is not hindered.

Water quality and availability has been a particular hot topic for several organizations in the past years.

The United Nations continuously debates and establishes goals that are focused in improving water

supply at a global scale. Despite the fact that the goals that were established back in 2008 were met

(UN, 2015), it is estimated that there are still 1.8 billion people that use water sources contaminated with

fecal matter, which is strongly correlated with the presence of pathogenic microorganisms (WHO, 2015).

This number, however, does not represent the full scale of the problem. In fact, if other kinds of

pollutants, such as arsenic, are also taken into account, the water quality problem is much larger than

the one predicted.

Regarding the people that are stricken with scarcity of potable water, it is known that, as suprising as it

may seem, some live in developed countries. In these countries, it is common for people that live in

regions far from huge urban centers to suffer from lack of potable water. This is due to the fact that, not

only these regions do not have a population large enough to make an efficient large-scale water

treatment plant viable, but also because of the fact that, since they are located far from a urban center,

the costs of connecting these low populated regions to the treatment plants located close to urban

centers is often prohibitive.

In recent years, the investment costs of small scaled treatment technologies have been continuously

decreasing due to the increase in the production efficiency of their components. An example of this is

the product of filtration membranes, whose price has been continuously dropping throughout the years.

This improvement naturally led to the possibility of establishing small scale water treatment systems to

supply water to more remote regions in which it wouldn’t be economically feasible to design large scale

treatment plants. In fact, there are some cases in which it has been shown that it was possible to reduce

the total costs of a treatment solution by 90% when a small scale solution was considered instead of a

large scale one (EPA, 2003). This inevitably leads to the conclusion that small scale water treatment

systems may have a fundamental role in addressing some water supply problems.

2

1.2 Motivation and goals

The motivation behind this document lies in the recent improvement of small scaled water treatment

systems in terms of cost-efficiency. This fact naturally leads to the questioning of how much did these

systems have improved and which kind of system is the most economically viable among them.

In order to answer these questions, this document aims at assessing the state of the art of small water

treatment solutions by analyzing the costs of different commonly used water treatment unit processes

using the WBS model established by EPA. On the other hand, in order to assess the most economically

viable solution for a treatment plant, it aims at establishing matrixes of water treatment solution costs

which take into account not only the amount of water consumed by a small sized population, but also

its raw quality.

1.3 Thesis’s structure

The first chapter introduces the global water quality problem and presents both the goal that this thesis

strives to achieve and the motivation behind it. Moreover, the overall structure of the thesis is also

presented in order to give the reader a more general view of how the goals are going to be achieved.

In the second chapter, after a brief initial introduction of the most relevant water quality parameters, the

Portuguese legal framework concerning both raw water quality and water quality required for human

consumption is assessed. Through the comparison of these frameworks, alongside with some extra

information regarding the occurrence of some water parameters, the water treatment requirements and

efficiencies are defined according to different raw water quality classes.

In the third chapter, the unit treatment cost analysis model that was adopted, the WBS model, or Work

Breakdown Structure model, is presented alongside with its assumptions.

Throughout the fourth chapter, by using the cost model defined in the third chapter and by considering

the treatment requirements and efficiencies defined in the second chapter, the investment costs of

different unit treatment processes are calculated.

The fifth chapter is dedicated to the estimation of investment costs of different residual management

alternatives. These costs, similarly to what was done in the fourth chapter, are also calculated based on

the WBS model previously established.

In the sixth chapter, a treatment scheme matrix is defined by taking into account the costs of each unit

treatment process and the water treatment requirements according to its raw water quality.

Throughout the seventh chapter, the costs of the treatment scheme matrix, defined in the previous

chapter, are presented and the results are then compared with other studies and discussed in terms of

their limitations.

Finally, in the eighth chapter, some conclusions are woven and some future research possibilities are

mentioned.

3

2 Water quality

2.1 Water quality parameters

Water quality is often measured by considering the concentration of certain water parameters. There

are different types of parameters that are often used and each country has, defined in its water treatment

legal framework, specific values for the concentration of each one of them. The following five groups of

parameters are the ones considered in the Portuguese water quality legal framework:

Organoleptic parameters;

Physical and chemical parameters;

Toxicological parameters;

Microbiological parameters;

Radiological parameters.

An organoleptic parameter measures a characteristic of the water that can be perceived by the human

senses. This group of parameters includes the color, smell, taste and the turbidity of the water. The

turbidity of the water is a parameter that measures its transparency and is strongly correlated with the

amount of total suspended soils in the water. The measurement of these parameters can be quite

subjective, but it is obvious that a treated water should have organoleptic characteristics that are

undetectable by the human senses.

Physical and chemical parameters characterize the water in terms of its physical and chemical

properties. This group includes parameters such as temperature, pH and total hardness. These

parameters are particularly relevant because of their fundamental role in the efficiency of the different

water treatment processes.

The toxicological parameters measure substances whose consumption in small amounts is particularly

hazardous for human health. This group, besides including synthetic organic compounds, includes

heavy metals such as arsenic, lead and chromium.

Microbiological parameters measure the level of contamination of pathogenic organisms such as

bacteria and viruses.

Last but not least, the radiological parameters measure the level of radioactivity of the water by

assessing the concentrations of different radionuclides, such as radon and tritium.

4

2.2 Portuguese legal framework for drinking water treatment

2.2.1 Raw water classification system

The Portuguese decree that classifies raw water destined for human consumption is the decree nº 236

of the 1st of August of 1998. Its 6th article defines a raw water classification system using three different

types of classes: Class A1, A2 and A3. The following Table 2.1 shows the maximum recommended

(MRV) and admissible (MAV) values for each class and for different water quality parameters.

Table 2.1 – Range of values of surface raw water parameters according to each water quality class

Parameter Units A1 A2 A3

MRV MAV MRV MAV MRV MAV

pH, 25ºC Sorensen scale 6.5-8.5 - 5.5-9.0 - 5.5-9.0 - Color mg/l Pt-Co 10 20 50 100 50 200 Total suspended soils mg/l 25 - - - - - Temperature ºC 22 25 22 25 22 25 Conductivity μS/cm 1000 - 1000 - 1000 - Smell Dilution factor 3 - 10 - 20 - Nitrates mg/l 𝑁𝑂3 25 50 - 50 - 50 Fluorides mg/l F 0.7-1.0 1.5 0.7-1.7 - 0.7-1.7 - Total extractable organic chlorine mg/l Cl - - - - - - Dissolved iron mg/l Fe 0.1 0.3 1 2 1 - Manganese mg/l Mn 0.05 - 0.1 - 1 - Copper mg/l Cu 0.02 0.05 0.05 - 1 - Zinc mg/l Zn 0.5 3 1 5 1 5 Boron mg/l B 1 - 1 - 1 - Beryllium mg/l Be - - - - - - Cobalt mg/l Co - - - - - - Nickel mg/l Ni - - - - - - Vanadium mg/l V - - - - - - Arsenic mg/l As 0.01 0.05 - 0.05 0.05 0.1 Cadmium mg/l Cd 0.001 0.005 0.001 0.005 0.001 0.005 Total chromium mg/l Cr - 0.05 - 0.05 - 0.05 Lead mg/l Pb - 0.05 - 0.05 - 0.05 Selenium mg/l Se - 0.01 - 0.01 - 0.01 Mercury mg/l Hg 0.0005 0.001 0.0005 0.001 0.0005 0.001 Barium mg/l Ba - 0.1 - 1 - 1 Cyanides mg/l CN - 0.05 - 0.05 - 0.05 Sulfates mg/l 𝑆𝑂4 150 250 150 250 150 250 Chlorides mg/lCl 200 - 200 - 200 - Tenso-active substances mg/l lauryl sulfate 0.2 - 0.2 - 0.5 - Phosphates mg/l 𝑃2𝑂5 0.4 - 0.7 0.005 0.7 -

Phenols mg/l 𝐶6𝐻5𝑂𝐻 - 0.001 0.001 0.2 0.01 0.1 Dissolved or emulsified hydrocarbon mg/l - 0.05 - 0.2 0.5 1 Poli-nuclear aromatic hydrocarbon μg/l - 0.2 - 2.5 - 1 Total pesticides μg/l - 1 - - - 5 Chemical oxygen demand mg/l 𝑂2 - - - - 30 -

Dissolved oxygen 𝑂2 % saturation 70 - 50 - 30 -

Biochemical oxygen demand mg/l 𝑂2 3 - 5 - 7 - Kjeldahl nitrogen mg/l N 1 - 2 1.5 3 -

Ammonia nitrogen mg/l 𝑁𝐻4 0.05 - 1 - 2 4 Chloroform extractable substances mg/l 0.1 - 0.2 - 0.5 - Total organic carbon mg/l C - - - - - - Residual organic carbon mg/l - - - - - - Total coliform /100 ml 50 - 5000 - 50000 - Fecal coliform /100 ml 20 - 2000 - 20000 - Fecal streptococci /100 ml 20 - 1000 - 10000 -

Salmonella - Undetected

in 5 L -

Undetected in 1 L

- - -

Adapted from the Appendix I of the Portuguese decree nº 236 of the 1st of August of 1998.

5

2.2.2 Water quality required for human consumption

After the water treatment process, some water parameters must comply with values that are defined in

the legal framework. The decree that establishes that target water quality is the decree nº 306 of the

27th of August of 2007. Its 6th article states that treated water must comply with the parametric values

that are included in Part I and II of the decree’s Appendix I. These values were compiled in the following

Table 2.2.

Table 2.2 – Treated water required parametric values

Parameter Parametric value Units

Escherichia coli 0 /100 ml Enterococci 0 /100 ml Acrylamide 0.5 μg/l Antimony 5 μg/l Arsenic 10 μg/l As Benzene 1 μg/l Benzo(a)pyrene 0.01 μg/l Boron 1 mg/l B Bromates 10 μg/l Cadmium 5 μg/l Cd Chromium 50 μg/l Cr Copper 2 mg/l Cu Cyanides 50 μg/l CN 1,2 - Dichloroethane 3 μg/l Epichlorohydrin 0.1 μg/l Fluorides 1.5 mg/l F Lead 10 μg/l Pb Mercury 1 μg/l Hg Nickel 20 μg/l Ni Nitrates 50 mg/l 𝑁𝑂3 Nitrites 0.5 mg/l 𝑁𝑂2 Individual pesticide 0.1 μg/l Total pesticides 0.5 μg/l Poli-nuclear aromatic hydrocarbon 0.1 μg/l Selenium 0.01 mg/l Se Tetrachloroethane and trichloroethane 10 μg/l Total trihalomethanes 100 μg/l Vinyl chloride 0.5 μg/l

Values compiled from Part I, II of the Appendix I of the Portuguese decree nº 306 of the 27th of August of 2007.

2.3 Raw water treatment efficiency requirements

In the preceding subchapters, different raw water quality classes were established and the water quality

required for human consumption was specified. Now, it is intended, through the comparison of Table

2.1 with Table 2.2, to establish removal efficiencies for each class and for each water quality parameter.

By comparing both tables, it is evident that they are not fully coherent in the parameters that they use

to characterize the water, and it is impossible, without any additional data, to establish ranges of values

for every parameter that is included in Table 2.2. In order to define the missing ranges of values, it was

decided to establish them arbitrarily while considering one fundamental aspect: their natural occurrence

in water. The natural occurrence of a pollutant gives an impression of what to expect for the classification

6

system. If the natural occurring concentration is close to the target parametric value required for human

consumption, the values that define the remaining classes should not be much higher than the target

value. On the contrary, if the occurring concentration was relatively far from the target, it was considered

reasonable to define this value has being close to an upper limit, or the A3 class so to speak.

The natural occurrence of most parameters was found in (WHO, 2011). However, there were some

parameters whose values were not found. In order to address this problem, a different approach had to

be chosen. In this case, the values for each of the classes were defined by extrapolating the target

parametric value of the pollutant. The values were extrapolated so that their corresponding class values

would have similar treatment removal efficiencies required as the already fully defined parameters. In

other words, if, for example, a pollutant has a target parametric value of 10 mg/l and the already defined

parameters have median removal efficiencies of 50, 80 and 90% for each one of the A1, A2 and A3

classes, respectively, then, its corresponding class values would be 20, 50 and 100 mg/l.

To conclude, it is also important to refer some aspects regarding some of the parameters included in

Table 2.2. According to the Portuguese legal framework, these parameters measure the water quality

that is necessary to assure at the point of consumption and not at the exit of the water treatment plant.

Therefore, lead, whose occurrence in high concentrations is most often due to the corrosion of pipes in

water supply systems, was not considered. Furthermore, other parameters such as acrylamide,

antimony and epichlorohydrin were also not included due to the fact that these are controlled by either

reducing or completely avoiding coagulating and flocculating reagents that include them and not by

including specific water treatment unit processes. In regard to cyanides, it is known that a high

concentration is often regarded as an abnormal occurrence for which no specific treatment processes

are usually designed. Last but not least, it is known that copper rarely exists in concentrations that are

hazardous for health and its treatment was also disregarded. For these reasons, these parameters were

not included in Table 2.3, displayed in the following page, which shows the treatment efficiencies

required.

7

Table 2.3 – Parameter range values and treatment efficiency requirements.

Parameter Target P.V.* Units A1 A2 A3

P.V. R.R.E** (%) P.V. R.R.E (%) P.V. R.R.E (%)

Total coliform 0 /100 ml 50 log 3 5000 log 5 50000 log 6

Fecal coliforms 0 /100 ml 20 log 3 2000 log 5 20000 log 6

Fecal streptococci 0 /100 ml 20 log 3 1000 log 5 10000 log 6

Arsenic 10 μg/l As 20 50 50 80 100 93

Boron 1 mg/l B 2 50 5 80 10 90

Bromates 10 μg/l 25 60 50 80 200 95

Cadmium 5 μg/l Cd 10 50 25 80 50 90

Chromium 50 μg/l Cr 100 50 125 60 200 75

Fluorides 1.5 mg/l F 6 75 10 85 50 97

Mercury 1 μg/l Hg 5 80 10 90 50 98

Nickel 20 μg/l Ni 100 80 250 92 500 96

Selenium 0.01 mg/l Se 0.05 80 0.2 95 0.5 98

Nitrates 50 mg/l 𝑁𝑂3 100 50 200 75 300 83

Nitrites 0.5 mg/l 𝑁𝑂2 1 50 5 90 10 95

Benzene 1 μg/l 5 80 10 90 50 98

Benzo(a)pyrene 0.01 μg/l 0.05 80 0.1 90 0.5 98

1,2 – Dichlorothane 3 μg/l 10 70 30 90 80 96

Individual pesticide 0.1 μg/l 0.2 50 0.5 80 1 90

Total pesticides 0.5 μg/l 0.8 37.5 1 50 5 90

Poli-nuclear aromatic hydrocarbon 0.1 μg/l 0.5 80 1 90 10 99

Tetrachloroethene and trichloroethene 10 μg/l 25 60 50 80 100 90

Total trihalomethanes 100 μg/l 200 50 500 80 1000 90

Vinyl chloride 0.5 μg/l 1 50 5 90 20 98

Pathogenic microorganisms

Heavy metals and inorganic substances

Synthetic organic compounds

* P.V - Parametric value. ** R.R.E. – Required removal efficiency.

2.4 Raw water characterization according to its origin

Before proceeding into the next chapter and into the cost analysis, it is opportune to delve more into the

distinction that both scientific literature and Portuguese legislation make between surface and

groundwater. As it will be noticed further ahead in chapter 6, this distinction will prove itself useful for

assessing the treatment costs for each type of water.

It is known that both types of water often have different predominant pollutants. Surface water samples

taken in the USA have shown that the presence of pathogenic agents in more than 77% of the samples

(LeChevallier & Norton, 1995) (Rose, 1988). In contrast to surface waters, these pathogenic agents

were only detected in about 12% of the samples taken from groundwater (Hancock, et al., 1998).

Additionally, it is intuitive that surface water is more susceptible to microbiological contamination due to

its open interaction with the biota. Therefore, it should be reasonable to consider that surface water

usually has higher treatment demands in terms of microbiological contamination than groundwater.

8

Despite having a lower microbiological contamination level, it is known that groundwater may contain

very high concentrations of inorganic compounds and heavy metals. In fact, studies have shown that,

due to the high concentration of inorganic compounds in the soil and the infiltration of heavy metal based

compounds that are used in industrial and agricultural activities, there’s a high occurrence of these

substances in groundwater (Shallari, et al., 1998) (AWWA, 1993). Arsenic is one common trace element

in groundwater and samples taken in the USA and Canada have evidenced the presence of this element

in concentrations above 10 μg/l in more than 10% of the wells sampled (Ayotte, et al., 2003) (Welch, et

al., 2000). High chromium concentrations are also common in groundwater located in industrialized

areas due to its wide industrial application (Palmer & Wittbrodt, 1990) (Powel, et al., 1995).

Both surface and groundwater must also be concerned with another particular group of pollutants, the

synthetic organic compounds. The occurrence of organic compounds in water has been widely studied

and samples of groundwater taken from 3,498 wells throughout the USA have evidenced the presence

of VOCs in 77% of the wells at concentrations above 0.2 μg/l (Carter, et al., 2008). As for the occurrence

of organic compounds in surface waters, semi-volatile organic compounds were detected in more than

71% of the 536 sampled streambed sediments across the USA (Lopes & Furlong, 2001). Also, in the

USA, it was shown that 23% of the systems that exclusively treated surface water and 27% of the

systems that treated groundwater indicated that VOCs were being treated (EPA, 1997).

Considering what was just exposed regarding the different groups of pollutants, it was decided to

distinguish both surface and groundwater through different levels of occurrence according to what is

shown in the following Table 2.4, which displays the range of classes defined for each group of pollutant.

Table 2.4 – Water class range according to its origin

Group of pollutants Surface water Groundwater

Microorganisms A2 – A3 A1 – A2

Inorganic substances and heavy metals A1 – A2 A2 – A3

VOC’s A1-A3

From Table 2.4 it is possible to observe that, contrary to groundwater, surface water was characterized

has having higher classes of microbiological contamination and lower classes of inorganic substances

and heavy metals. As for synthetic organic compounds, it was defined that both types of water are

subject to similar pollutant occurences.

Another relevant point, not shown in Table 2.4, and that must be account for, is the fact that surface

water is often more affected by turbidity and sediments than groundwater. Groundwaters often have low

turbidities due to filtration of sediments that occurs through the water’s percolation and, as a result, this

type of water doesn’t often require a turbidity removal process.

9

3 Water treatment unit process cost analysis model

3.1 General overview

Before proceeding into the description and the cost analysis of the different treatment and residual

management processes, it is fundamental to introduce the models that were the foundation of the

analysis. The models that were used were the “Work Breakdown Structure-Based Cost Models”, or

WBS, developed by the United States Environmental Protection Agency (EPA).

These models were conceived with the aim of estimating the compliance costs of existent water

treatment systems due to amendments in American water quality standards. The structure of these

models, as it shown in the following Figure 3.1, is composed of two parts, the WBS engineering analysis

and the WBS system cost analysis.

Figure 3.1 – WBS model structure

Taken from Exhibit 2-1 in WBS-Based Cost Models for Drinking Water Treatment Technologies. (EPA, 2014)

10

As it is possible to observe in Figure 3.1, everything that is related to the design of the treatment process

is defined in the WBS engineering analysis. First, in the input sheet, the user must input fundamental

design parameters that are relevant for the design such as the flow rate and the treatment efficiency

required. Additionally, in the same sheet, the user must also define other aspects such as the level of

quality of the materials to be used or the level of automation of the system. Afterwards, when the user

advances into the critical design assumptions sheet, he must evaluate whether the predefined design

assumptions are in accordance with what he pretends. After the required data is totally inputted in both

sheets, the model chooses specific components that are able to materialize the treatment system. These

components are then passed on to the second part of the model so that their costs might be evaluated.

In the WBS system cost analysis, in order to assess their costs, the components that were previously

defined are compared with either cost equations or cost databases. These cost equations, which were

established by EPA through the information gathered from different water treatment plants, can be used

to know the cost of components as a function of the design parameters. As for the costs databases,

these were conceived through the inquiry of component manufacturers and through the research of

engineering reference data. After the definition of the costs of each component, the model proceeds into

calculating the O&M and the indirect costs based on what was defined in the engineering analysis. Being

the component costs calculated, as well as the O&M and indirect costs, the model displays the outcome

of the cost analysis in the output sheet in the form of five different costs, whose assumptions are further

detailed below in the following subchapters.

3.2 Direct capital cost

The direct capital costs comprise the costs directly related to the treatment technology. These include

the following:

System equipment costs (e.g. chlorine dioxide generators, UV reactors, reverse osmosis

membranes, etc.);

Costs with piping, pumps and valves;

Cost with instrumentation (e.g. pH meters, turbidity meters, flow meters, alarms) and system

controls (e.g. operator interface units and software);

Costs with the building’s structure.

All of these costs, excluding the ones with the building’s structure, have a similar way of being calculated.

EPA calculates these costs by initially obtaining a vendor quote, then adding an estimated transportation

rate, and, in the end, by adjusting the resultant value using an installation and contractor overhead and

profit adjustment factor. According to (EPA, 2014), these adjustment factors are between 1.03 and 1.73

and have an average value of 1.36.

The approach that was followed for the direct cost analysis of the unit treatment processes that were

not provided in the EPA’s website was slightly different. Since the component and system manufacturers

are located throughout the world and the transportation rate is difficult to quantify, it was decided to use

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a conservative adjustment factor that would include this parcel. It is known that the most common way

of shipping goods is through ocean shipping. According to (Hummels, 2007), the ad valorem ocean

freight cost, which is the cost of transportation according to the value of the shipped product, has been

steadily decreasing throughout the years and in 2004 it had a value of about 6%. Taking this value into

account, the range of adjustment factors used by EPA, and considering that there might also be some

additional land transportation, it was decided to use a rather conservative general adjustment factor of

2. The only exception was for chemicals such as chlorine gas, ferric chloride or aluminum sulfate. Since

these materials only require an adjustment factor for their transportation, a lower value of 1.1 was

assumed.

Regarding the piping, pump and valve costs, it was assumed that the unit prices would be the same as

the ones available in the WBS models. Additionally, it was also assumed that each unit process would

require 10 m of piping for the treatment process and another 10 m in case backwash was required.

As for instrumentation, the unit costs of the WBS model were maintained. However, some instruments

were not included due to their prohibitive costs towards small scale treatment plants. An example of this

are the turbidity meters, which can cost in the range of the thousands of euros. Table 3.1 shows the

instruments included and their corresponding assumptions.

Table 3.1 - System instrumentation assumptions

Instrument type Assumption

Chlorine analyzers For chlorine and hypochlorite disinfection, 1 per treatment train. Drive controllers 1 per pump or other motorized item of equipment (e.g., mixers) in fully automated systems. Flow meters 1 for the influent or effluent line and 1 for backwash discharge. Pressure sensor 2 per process vessel for technologies with pressure vessels High/low alarms 1 per backwash tank and 1 per chemical storage tank. pH meters 1 each for the influent and effluent lines for systems with pH adjustment. Sampling ports 1 per process vessel, plus 1 each for the influent line, effluent line and discharge side of the

backwash line. Temperature meters 1 for the influent and/or effluent lines.

Adapted from Exhibit A-1 in WBS-Based Cost Models for Drinking Water Treatment Technologies. (EPA, 2014)

Still concerning the direct costs of components, the WBS models also require the definition of the level

of quality of the different system components used and of the level of automation required for the system.

The former one, due to the fact that the envisioned treatment system is small scaled, it was assumed

that the components were of a low quality level, which corresponds to the use of materials such as PVC.

As for the level of automation, in order to reduce overall costs during the lifespan of the treatment

system, a fully automatic level was assumed. The following Table 3.2, displayed in the following page,

shows the design assumptions made for a fully automated control system.

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Table 3.2 – Fully automated system control design assumptions

Item of control equipment Assumption

PLC Rack/Power Supply 1 per system CPU 1 per system I/O Discrete output module 1 for every 32 outputs I/O Discrete input module 1 for every 32 inputs I/O Combination module 1 for every 12 output and inputs Ethernet module 1 per system UPS 1 per system Operator interface unit – advanced, fully functional 1 per system Operator interface software 1 per system

Adapted from Exhibit A-3 in “WBS-Based Cost Models for Drinking Water Treatment Technologies”. (EPA, 2014)

Last but not least, the cost of the building’s structure was determined by using cost values per square

meter calculated by EPA and the building’s calculated required footprint. As it is explained in (EPA,

2014), the cost values were calculated using the Craftsman NBCE model, which is a software that

generates building cost estimates based on user inputs regarding the building’s size and the quality of

its features. These inputs were taken by EPA from the RSMeans and Saylor manuals, which contain

unit costs for various building components in terms of costs per unit of area. Also, it should be mentioned

that the previous assumption that was made regarding the quality level of the system components also

affects the quality of the building. Thus, by virtue of the level chosen, the cost values per square meter

used in the cost estimations of unit processes are those of a very small low quality building (i.e. a shack)

or of a low quality building in case there’s a unit process that requires ventilation such as ozonization.

As for the area of the building, it was calculated by summing the required area for each system

component while considering an extra space of 1 m to each of its dimensions to allow enough space for

the replacement of parts and maintenance. Additionally, if a specific unit processes required it, a specific

area was also designated for the storage of chemicals. This area was calculated by taking into account

the size of its chemical containers and assuming a monthly resupply rate.

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3.3 Indirect capital cost

Indirect capital costs are those related to the construction and installation of a unit treatment process.

The items considered in the indirect capital costs, as well as their respective direct capital percentages,

are shown in the following Table 3.3.

Table 3.3 – Indirect capital item costs as a percentage of total direct capital costs

Indirect capital costs item Percentage of direct costs

considered

Mobilization and demobilization Technology specific Architectural fees for treatment building 0% Site work 5% Standby power 0% Electrical system 10% of the building direct costs Process engineering 20% Contingency costs Complexity factor times 6.7% Miscellaneous allowance 5% Legal, fiscal and administrative 2% Sales tax 0% Financing during construction 0% Construction management and general contractor overhead Depends on the direct cost Yard piping Technology specific Geotechnical investigation Technology specific

Regarding mobilization and demobilization, through the analysis of different water treatment plants, EPA

reached the conclusion that the range of values that is expectable for this item ranges from 2 to 5% and

that this value is higher for smaller projects due to the fact that fixed costs tend to be the same regardless

of the project size. However, since small scaled systems are usually pre-engineered packed systems

and don’t require equipment mobilization and demobilization, a percentage of 0% was assumed for most

processes. The only exceptions to this assumption are evaporation ponds and septic tanks. By virtue of

the volume of excavations that these alternatives require, a percentage of 5% was assumed.

The architectural fees for the building include the costs of designing the structure and preparing technical

drawings. Since small water treatment systems are typically housed in small prefabricated buildings,

that require minimum design and engineering, it was assumed that there was no architectural fee.

Site work costs depend on the site conditions and the overall size of the treatment plant. According to

EPA, the value for this cost ranges between 5 and 15%. By taking into account the small area required

for the treatment plant and by assuming that the site didn’t require any major improvements, a

percentage of 5% was chosen for this indirect cost item.

As for the system standby power, since small systems typically operate for only a few hours per day and

can handle short term power outages by simply postponing their operating hours, it was assumed that

there was no need to include a standby power system and, thus, the percentage assumed was 0%.

The electrical cost allowance in a construction cost estimate will primarily account for electric wiring

inside structures. It should be noticed that since the direct costs related to the building already

incorporate some lighting costs related to the general building electrical system, the indirect cost

14

electrical allowance only accounts for additional electrical equipment associated with the treatment

facility, including outdoor lighting, yard wiring, switchgear, transformers and miscellaneous wiring. For

this item, a value of 10% of the process costs (direct capital costs minus building costs) was assumed.

Process engineering costs include costs with the treatment process design, unit operation construction

supervision, travel, system start-up engineering and production of record drawings. The percentage

value usually ranges from 5 to 20% and depends on the complexity of the processes and the system

size. It was decided to keep the default value of 20% defined by EPA.

Contingency costs account for the degree of risk assigned to a project. These cost reflect the statistical

probability of additional project costs due to uncertainties and unlikely unforeseen events. The

percentage of these costs depends on the project base cost. EPA analyzed empirical data related to

heavy industrial projects and other water service recommendations and established a base value for

the contingency costs of 6.7% for projects under 400,000 €. Since different treatment technologies have

different complexities, this percentage must also be adjusted according to the complexity that a specific

technology displays. In Table 3.4 the different complexity factors for each technology are shown. For

the unit processes that are analyzed in the following chapter and that are not included in the Table 3.4,

an equivalent complexity factor of comparable technologies was assumed.

Table 3.4 – WBS default complexity factors by technology

Technology Risk level assigned to technology Default complexity factor

Acid feed Low 0.5

Cationic exchange Low 0.5

Caustic feed Low 0.5

Nontreatment options Low 0.5

Potassium permanganate addition Low 0.5

Granular activated carbon Average 1

Chlorine gas Average 1

Packed tower aeration Average 1

Adsorptive media High 1.5

Anion exchange High 1.5

Biological treatment High 1.5

Microfiltration and ultrafiltration High 1.5

Greensand filtration High 1.5

Hypochlorite addition High 1.5

Multi-stage bubble aeration High 1.5

Reverse osmosis and nanofiltration High 1.5

Ultraviolet advanced oxidation processes Very high 2

Ultraviolet disinfection Very high 2

Taken from Exhibit D-7 in WBS-Based Cost Models for Drinking Water Treatment Technologies. (EPA, 2014)

Proceeding further, in the sphere of cost estimation, a miscellaneous allowance is a share of the costs

that is allotted to shield against the uncertainty of the costs related to some site conditions or events

that the estimator can anticipate. It differs from a contingency costs because these provide contract

15

coverage for unpredictable conditions. Although WBS models assume a miscellaneous allowance of

10%, it was chosen to reduce this value to 5% because of the scale of the treatment system.

The legal, fiscal and administrative costs account for the costs that the purchaser incurs in the course

of procurement. The value usually ranges from 2 to 5%. A default value of 2% was chosen.

With regard to the sales tax cost percentage, a value of 0% was chosen. This value reflects the status

of taxes when water treatment plants are exempt from sales tax by being funded with public funds.

The financing costs during construction refer to the loans interest that must be covered. A value of 0%

was considered for this item due to the fact that small water treatment plants have short construction

times.

As for the construction management and general contractor overhead item, it includes the following

costs:

Builders risk insurance;

Performance bonds;

Construction management.

For the builders risk insurance, which is an insurance for casualties such as vandalism, fire or theft, EPA

established a value of 0.34%. This value is the national average estimated by the RSMeans in the USA.

The second cost, the performance bonds cost, compensates the owner for losses due to contractor

failure in completing work according to specifications. Their cost is shown in the following Table 3.5.

Table 3.5 – Cost of performance bonds

Project direct cost range Performance bond cost

< 88,000 € 2.5%

88,000 to 440,000 € 2,200 € plus 1.5% the amount over 88,000€

Adapted from Exhibit D-9 in WBS-Based Cost Models for Drinking Water Treatment Technologies. (EPA, 2014)

As for the construction management fee, it is paid to a general contractor to cover the cost of jobs

supervision, an on-site office and the main office overhead and profit. Once again, due to the fact that

small water treatment plants are often compact pre-engineered packages, whose installation and

supervision is done by the package vendor, there’s no need for a general contractor and this fee might

be disregarded.

Yard piping costs reflect the costs of installing piping to and from the site, between new treatment plant

buildings and between existing or new treatment units. This cost is technology specific and cannot be

generalized into a percentage. Yard piping costs include the following components:

Trench excavation, backfill and pipe bedding;

16

Piping from the boundary of the building buffer zone to and from the building inlet and building

outlet and in between buildings that house water treatment components;

Thrust blocks.

To conclude, similarly to yard piping, the inclusion of geotechnical investigation is also technology

specific. It was assumed that these costs were to be disregarded in most cases and the only exception

to this assumption would be the septic systems and evaporation ponds. According to what it is shown

in the following Table 3.6., the estimation of these costs is based on the footprint area of the evaporation

ponds or the drainage area of the septic systems.

Table 3.6 – Cost of the geotechnical investigation

Area (m2) Geotechnical tests Geometrical dimensions Costs of the geotechnical tests

< 184 1 pit per 92 m2 1.2 x 1.2 x 1.8 m 217.11 €/m3

> 184 1 bore hole per 92 m2 3 m 284.16 €/m

Values taken from the 7th subchapter of Appendix D of WBS-Based Cost Models for Drinking Water Treatment Technologies. (EPA, 2014)

3.4 Annual O&M cost

The annual operation and maintenance cost, or O&M, includes three types of expenses:

Expenses with labor;

Expenses with materials needed for the operation and maintenance;

Expenses with energy required for the system operation, lighting, heating, cooling and

ventilation.

Regarding labor expenses, there are three types that are considered in the WBS models:

Manager labor expenses;

Administrative labor expenses;

Operational labor expenses.

The expenses related to labor depend fundamentally on the amount of time that is spent by an operator

in executing tasks such as verifying and calibrating the process instruments. The assumptions

concerning the operator tasks are shown in Table 3.7, which is displayed in the following page. The

WBS models also assume that both manager and administrative labor times are each 10% of the

operational labor.

As for the hourly rates of each labor type, it was decided to keep the default values of the WBS model,

which are 35.92 €/h for the manager, 27.92 €/h for the administrative and 25.36 €/h for the operational

labor.

17

Table 3.7 – Operator labor assumptions

Task Level of Automation

Manual Semi-automated Automated

Record system operating parameters from process instruments (includes routine sampling)

5 minutes per day per instrument

5 min per day

Preventative maintenance and calibration of process instruments

10 minutes per month per instrument

Verify and adjust pump operating parameters 5 minutes per day per pump None

Preventative maintenance of pumps 30.25 hours per pump

Verify and adjust valve positions 5 minutes per day per valve None

Preventative maintenance and inspection of valves

5 minutes per year per valve

Visual inspection of the facility 1 minute per day per 9.2 m2 of facility

Inspect and maintain chemical supplies 60 minutes per month per chemical supply tank

Taken from Exhibit E-1 in WBS-Based Cost Models for Drinking Water Treatment Technologies. (EPA, 2014)

With respect to the expenses with the materials needed for the operation, there are three types that the

models take into account:

Reagents used during the treatment process;

Materials required for the system and pump maintenance;

Materials and repair tasks required for the building maintenance.

As its name suggests, the first type concerns the expenses with the reagents used during the treatment

processes (i.e. chlorine, activated carbon, ferric chloride, etc.). Regarding the price of these reagents,

although the WBS models have a considerable array of prices defined, the price of some of them had

to be assessed through different suppliers.

As for the second type of expenses, the WBS models assume a yearly cost of 1 and 4% of the process

cost (i.e. cost of the system, pipes and valves) for the pumps and system, respectively.

Last but not least, EPA assumes a value of 50.55 €/m2/yr for the building maintenance based on the

materials and repair tasks needed as defined by the Whitestone Research and RSMeans.

As for the total energy expenses, these are composed by three different types:

Energy expenses with electrical equipment;

Energy expenses with lighting;

Energy expenses with heating, cooling and ventilation of the building.

The energy expenses with the electrical equipment includes the energy that is used by pumps and other

electrical systems such as electrical measuring devices, computers and chemical generators such as

sodium hypochlorite generators.

18

As for the energy expenses with lightning, these are based on the quality level of the building. The WBS

models define a value of 11 W/m2 for the energetic consumption of sheds and low quality buildings.

For third and final energy expense, the WBS models establish that buildings of a low quality or inferior

don’t require neither heating nor cooling, and that the only component that must be accounted for is the

ventilation, which is calculated using the following Equation (1):

𝑉𝑒𝑛𝑡𝑖𝑙𝑎𝑡𝑖𝑜𝑛 𝑒𝑛𝑒𝑟𝑔𝑦 (𝑀𝑊ℎ 𝑦𝑟⁄ ) = 152,36𝐷. 𝑃𝑑𝑟𝑜𝑝. 𝐹𝑝. 𝐻. 𝐴𝑐ℎ𝑎𝑛𝑔𝑒𝑠 33000000⁄ (1)

where:

𝐷 = days per year with mechanical ventilation (d/yr);

𝑃𝑑𝑟𝑜𝑝 = pressure drop across ventilation fans (kN/m2);

𝐹𝑝 = building footprint (m2);

𝐻 = building height (m);

𝐴𝑐ℎ𝑎𝑛𝑔𝑒𝑠 = weighted average air change rate for the building (air changes/ hour).

The values assumed for the variables of Equation (1) are shown in the following Table 3.8.

Table 3.8 – Values assumed for the ventilation energy equation variables

Variable Value used

Ventilation air change rate 20 air changes/hour Pressure drop across ventilation fans 0.238 kN/m2 Number of days with mechanical ventilation 90 days/yr

Building height 3 m

Adapted from Exhibit E-4 in WBS-Based Cost Models for Drinking Water Treatment Technologies. (EPA, 2014)

To conclude, it should be noted that the energetic cost that was assumed was of 0.1 €/kWh.

3.5 Add-on cost

Add-on costs are costs that may be attributed to one or more aspects of the treatment technology. These

include permit costs (e.g. construction and discharge permits), pilot or bench testing costs and land use

costs. Among these, with the aim of simplifying the cost estimation process, it was decided to include

only the discharge permits, which are addressed in chapter 5, and the land used costs.

The land use costs have two components, one is the area required by the building and the other one is

the area that might be needed for residual management purposes such as evaporation ponds or septic

tanks.

The building area is calculated similarly to what was already explained in subchapter 3.2, but in this

case it was also assumed that the building required some extra space in its exterior in case of fire.

Therefore, while assuming that the building has a width/length ratio of 1, a fire buffer of 12 m was added

to one of its sides and a non-fire buffer of 3 m was added to the three remaining ones.

As for the other component, the area required for evaporation ponds or septic tanks was calculated from

their design requirements and a buffer of 3 m was subsequently added to each one of their sides.

19

Last but not least, it was considered reasonable to assume a land cost of 5 €/m2, which is more

conservative than the values between 2 and 4.5 €/m2 assumed in the WBS models.

3.6 Total annualized cost

The total annualized cost is calculated by annualizing direct, indirect and add-on costs and subsequently

adding them the O&M costs. In order to annualize the different costs, it was necessary to estimate a

useful life for the system and to assume a discount rate. While the discount rate was simply assumed

as being 6%, the useful life, since it varies by component type and material, had to be calculated using

a weighted average approach by considering the useful life of each individual component and its weight

in the direct capital costs. The following Equation (2) shows the useful life weighted average formula

applied:

𝑈𝑠𝑒𝑓𝑢𝑙 𝑙𝑖𝑓𝑒 =

∑ (𝐶𝑛. 𝑈𝑛) +𝑁𝑛=1 𝐴𝑐𝑜𝑠𝑡 + 𝐼𝑐𝑜𝑠𝑡

∑ 𝐶𝑛𝑁𝑛=1 +

𝐴𝑐𝑜𝑠𝑡 + 𝐼𝑐𝑜𝑠𝑡

𝑈𝑏𝑢𝑖𝑙𝑑𝑖𝑛𝑔

(2)

where:

𝐶𝑛 = cost of component n, from 𝑛 = 1 to 𝑁;

𝑈𝑛 = useful life of component n, from 𝑛 = 1 to 𝑁;

𝐴𝑐𝑜𝑠𝑡 = total add-on costs;

𝐼𝑐𝑜𝑠𝑡 = total indirect capital costs;

𝑈𝑏𝑢𝑖𝑙𝑑𝑖𝑛𝑔 = useful life of the building.

3.7 Other assumptions

Before proceeding into chapter 4, it’s fundamental to refer some other assumptions that were required

for the cost-analysis. With the perspective of presenting the system costs as a function of the daily

treatment capacity, a daily treatment capacity range of values was defined by the two following minimum

and maximum values, both based on assumed daily consumptions and population sizes:

The minimum value is 15 m3 per day. This value represents a daily water consumption

of 30 l per person by a population size of 500 people.

The maximum value is 450 m3 per day. This value represents a daily water consumption

of 150 l per person by a population size of 3,000 people.

The design flow of the treatment system was calculated by multiplying both median daily consumption

limits by an assumed monthly peak flow factor of 1.3.

Furthermore, given the scale of the treatment systems, it was also assumed that the daily operation time

was 8 h. While taking this value into account, it was also assumed that there is only one treatment line

since the treatment has the flexibility of being postponed.

20

4 Cost analysis of unit treatment processes

4.1 Aeration

4.1.1 Packed tower aeration

Aeration is a process through which the quality of the water is improved by its contact with the

atmospheric air. Packed tower aeration, or PTA, consists in the flow of water through a media that is

contained in a cylindrical container and that is designed to increase the water contact surface with the

atmospheric air that is pumped in the opposite direction.

This process has two applications, the first of them is the oxidation of heavy metals and inorganic

substances and the second is the removal of synthetic volatile organic compounds, or VOCs. However,

due to the fact that it has been shown that aeration is not an efficient process in the oxidation of

compounds such as As(III) (Lowry & Lowry, 2002), it was assumed that these processes would only

target VOCs.

The design of a PTA system is based on Onda’s equations which explain the rate of transference of a

volatile substance from the water to the air. Among all the variables included in the equations, when

comparing different pollutants under similar physical and chemical conditions, the most significant is the

Henry’s constant. It is known that, the amount of a gas dissolved in a liquid is directly proportional to this

constant and the higher this constant is, the more easily can a VOC be removed from water.

Since the cost estimation of the PTA process depends both on the target VOC and on the treatment

efficiency required, in order to simplify the problem, a more general approach was chosen instead of

analyzing specific situations with different types of VOCs at different concentrations. This general

approach consisted of analyzing two VOCs at two extreme situations, one where the concentrations of

the VOC with highest Henry’s constant is at a A1 level and another where the VOC with the lowest

Henry’s constant value is at a concentration of a A3 treatment requirement. This allows to establish a

range of cost values that is somewhat representative of the costs required for VOC treatment if

unreasonable situations, such as an A3 level treatment requirement for several VOCs, are overlooked.

21

The first step in establishing the range of costs comprised of the assessment of the Henry’s constants

of the VOCs previously included in Table 2.3. This values were compiled in the following Table 4.1.

Table 4.1 – Henry’s constants of the VOCs considered in the analysis

Volatile organic compound Henry’s constant2 (atm m3/m3) Source

Vinyl chloride 8.89E-01 (Wilhelm, et al., 1977)

Benzo(a)pyrene 2.55E-01 (EPA, 1986)

Benzene 2.27E-01 (EPA, 1986)

1,2 - Dichloroethane 4.49E-02 (EPA, 1986)

Tetrachloroethene and trichloroethene1 1.78E-02 (EPA, 1986)

1. Since the goal is to search for the highest and lowest Henry’s constant among these VOCs, due to the fact that trichloroethene has a value for the Henry’s constant between the one of benzo(a)pyrene and vinyl chloride, it was disregarded and the value shown corresponds to the 1,1,2,2 - tetrachloroethene. 2. The values for the Henry’s constants are in different units in the source documents.

It should be regarded that Henry’s constants are influenced by the temperature. However, since their

value varies somewhere in between 10 and 20% when the temperature changes varies from 10 to 20 ºC,

it was assumed that the the WBS model default safety factor of 1.4 was enough to cover this variation

so that it wouldn’t influence the choice of neither high nor low-end VOCs.

Based on Table 4.1, the VOCs that were initially chosen were vinyl chloride and the 1,1,2,2 –

tetrachloroethane. However, during the cost analysis, it was realized that the WBS model couldn’t design

a packed tower capable of treating 1,1,2,2 – tetrachlorothane at a A3 level due to the fact that the design

couldn’t comply with the model’s engineering design constrains. Therefore, 1,1,2,2 – tetrachloroethane

was replaced by the VOC with the second lowest Henry’s constant, 1,2 – Dichloroethane.

As for the WBS model inputs, after defining the target VOCs, it was assumed that there was no

disinfection clearwell and the type of media used were the polyethylene Jaeger Tri-packs of 50 mm.

Without further ado, the resulting costs for the PTA system are shown in the following Table 4.2.

Table 4.2 – Estimated cost range for a PTA system as a function of treatment capacity

Contaminant Parameter Daily treatment capacity (m3)

15 50 100 200 300 450

Vinyl chloride

Useful life (years) 19.4 19.4 19.4 19.5 19.5 19.5

Total capital costs (k€) 55.3 58.5 62.5 67.5 69.1 74.2

Total O&M costs (k€) 3.8 4.0 4.1 4.3 4.3 4.3

Total AAC (k€) 8.8 9.2 9.6 10.2 10.4 10.9

Cost per m3 (€) 1.605 0.502 0.263 0.140 0.095 0.066

1,2 – Dichloro ethane



Total O&M costs (k€) 4.4 5.2 6.1 7.1 8.1 9.9

Total AAC (k€) 10.9 13.8 16.5 18.9 21.9 27.1

Cost per m3 (€) 1.989 0.756 0.452 0.259 0.200 0.165

22

4.1.2 Diffused aeration

Diffused aeration works based on the same principle as PTA. However, although having the advantage

of providing a higher contact time of the air with the water, when compared with PTA, diffused aeration

allows for a smaller contact area for gas transference between the water and the air. The process

consists of the flow of the water through rectangular shaped tanks which have an air bubbles diffusing

system at the bottom.

Similarly to the PTA process, diffused aeration is rather incapable of removing inorganic compounds

with decent efficiencies. So, in the same manner as it was done for the PTA system analysis, two VOCs

were chosen in order to establish a range of cost values for the system. Once again, since diffused

aeration efficiency depends on the Henry’s constant, the choice fell on the vinyl chloride with a A1

treatment requirement and on the 1,1,2,2 – Dichloroethane with a A3 treatment requirement.

In the WBS model provided by EPA, the geometry of the diffusing basins was automatically calculated

using the already established algorithm. The only input required in the model was the air/water ratio

which had to be adjusted so that the expected efficiency of the treatment process would match the vinyl

chloride A1 treatment requirement and the 1,1,2,2 – Dichloroethane A3 treatment requirement. The cost

estimation for the diffused aeration system is shown in the following Table 4.3.

Table 4.3 – Estimated cost range for a diffused aeration system as a function of treatment capacity


15 50 100 200 300 450

Vinyl chloride


Total capital costs (€) 118.3 120.2 123.9 128.4 130.2 146.4

Total O&M costs (€) 3.5 3.5 3.6 3.8 4.0 4.3

Total AAC (€) 14.5 14.8 15.2 15.8 16.1 17.9

Cost per m3 (€) 2.657 0.810 0.417 0.216 0.147 0.109

1,1,2,2 Dichloro ethane


Total capital costs (€) 120.8 132.8 147.1 171.2 194.0 287.4

Total O&M costs (€) 3.7 4.5 5.5 7.5 9.5 14.3

Total AAC (€) 15.0 16.8 19.2 23.2 27.3 40.3

Cost per m3 (€) 2.745 0.923 0.525 0.318 0.249 0.245

4.2 Adsorption

Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.

Inside the sphere of water treatment, this process can be applied by making the water flow through a

porous, adsorbent substance with a very high specific surface area value. There are two types of

adsorption substances that are often used in water treatment, these are the activated alumina (AA) and

the activated carbon (AC).

23

Activated carbon is the most commonly used adsorbent due to its availability. It can be used either in a

powdery form (PAC) or in a granular form (GAC) for both smell or odor control and VOC adsorption.

Although having a similar scope of application when compared with GAC, PAC is a more refined and

expensive form of activated carbon often used to address intermittent or sporadic contamination

situations in conventional filtration systems. Hence why the PAC form was disregarded in the cost

estimation of the unit process and only the GAC form was taken into account.

As for the activated alumina, it has a different application scope when compared with GAC. Activated

alumina aims at adsorbing heavy metals and other inorganic substances such as arsenic. In fact, it has

been shown that, in two particular small scale treatment plants, AA adsorption reached arsenic removal

efficiencies above 90% (Wang, et al., 2002). Also, in addition to its high efficiency, it is known that this

compound is economical and readily available. However, contrary to GAC, it produces toxic residuals

at the end of its backwash filtration cycle which may turn the residual management process prohibitively

expensive.

An adsorption filtration system might operate either under pressure or due to gravity. Since gravity

filtration systems are primarily used in larger scale systems due to their design flexibility (AWWA &

ASCE, 1998), these were disregarded.

In order to estimate the costs of either AA of GAC filtration, there are two fundamental parameters that

must be defined, these are the life expectancy of the adsorbing material and the empty bed contact time,

or EBCT.

The life expectancy of the adsorbing material is a function of the rate of adsorption of a specific

contaminant and its influent and breakthrough concentrations. While the influent and breakthrough

concentrations are defined by the concentration values of the different treatment requirement classes

previously defined in chapter 2.3, the rate of adsorption may be explained according to the Freundlich

adsorption isotherm formula shown in the following Equation (3):

𝑥

𝑚= 𝐾. 𝑐1 𝑛⁄ (3)

where:

𝑥 = mass of adsorbate;

𝑚 = mass of adsorbent;

𝑐 = equilibrium concentration of adsorbent;

𝐾 and 𝑛 are constants for a given adsorbate and adsorbent at a particular temperature.

Similarly to the PTA and diffused aeration processes, the cost analysis will focus on a specific range of

values that is going to be defined by two VOCs that assure the highest and lowest values for the life

expectancy. To achieve this, the 𝐾 and 𝑛 constants for each VOC were searched throughout the

scientific literature in order to assess the adsorbability of each contaminant. Table 4.4, displayed in the

following page, shows the median reported values for the 𝐾 and 𝑛 constants of the considered VOCs.

24

Table 4.4 – Reported Freundlich isotherm 𝑲 and 𝒏 values of the VOCs considered in the cost estimation

Volatile organic compound 𝑲 ((μg/g)(l/ μg)) 𝒏 (adim.) Source

Vinyl chloride - - -

Benzo(a)pyrene 33,600 2.270 (EPA, 1980)

Benzene 1,260 0.533 (Speth & Miltner, 1990)

1,2 - Dichloroethane 129 0.533 (Speth & Miltner, 1990)

Trichloroethene (TCE) 2,000 0.482 (Speth & Miltner, 1990)

Tetrachloroethene (PCE) 7,760 0.682 (Erto, et al., 2009)

By observing Table 4.4, it is possible to conclude that benzo(a)pyrene is the most adsorbable

contaminant by virtue of its 𝐾 and 𝑛 values which are the highest among the considered VOCs. This

last fact, alongside the low concentrations at which this contaminant is expected to occur in natural

waters, makes it the less concerning contaminant regarding the life expectancy of the GAC layer.

1,2 - Dichloroethane, on the contrary, is the most constraining one.

As for the definition of the EBCT, it is known that this value is usually between 5 and 25 min (AWWA &

ASCE, 1998) and, as such, a 10 minute value was chosen. Based on this value and by using the WBS

in-built GAC pressure vessel auto-sizing algorithm, while assuming a backwash frequency of 48 h, the

GAC system costs were calculated and compiled in the following Table 4.5.

Table 4.5 – Estimated cost range for a GAC adsorption system as a function of treatment capacity


15 50 100 200 300 450

Benzo(a)pyrene



Total O&M costs (k€) 2.0 2.0 2.6 2.5 2.9 3.3

Total AAC (k€) 6.8 7.4 11.0 12.7 15.3 18.4

Cost per m3 (€) 1.240 0.407 0.301 0.174 0.140 0.112

1,2 - Dichloro ethane

Total O&M costs (k€) 4.4 9.7 17.4 31.1 44.9 64.9

Total AAC (k€) 9.3 15.1 25.8 41.3 57.3 80.1

Cost per m3 (€) 1.690 0.829 0.707 0.566 0.523 0.487

Note: The useful life and capital costs are the same for contaminants.

In the case of AA adsorption, the cost analysis was made by considering arsenate as the target pollutant

instead of VOCs. It has been shown that the value of the 𝐾 and 𝑛 constants of arsenate for an activated

alumina adsorbent were 1679 (μg/g)(l/μg) and 2.212, respectively (Wang, et al., 2002). Similarly to GAC,

an ECBT value of 10 min and a backwash every 48 h were chosen and assumed. The costs calculated

for the AA adsorption system are shown in the following Table 4.6, displayed in the following page.

25

Table 4.6 – Estimated cost for an activated alumina adsorption system as a function of treatment capacity

Parameter

Daily treatment capacity (m3)

Contaminant 15 50 100 200 300 450

Arsenate

Useful life (years) 16.3 16.7 17.5 18 20.6 21


Total O&M costs (k€) 3.8 4.7 6.7 9.4 12.5 16.9

Total AAC (k€) 8.5 9.9 14.8 18.7 23.7 30.4

Cost per m3 (€) 1.557 0.543 0.405 0.256 0.217 0.185

4.3 Coagulation

Coagulation is a process in which a positively charged coagulant, usually an aluminum or iron salt, is

added to raw water after being mixed into a solution in a rapid mix chamber. This coagulant aims at

destabilizing negatively charged contaminants so that they can aggregate and increase in nominal size.

This increase in size, in turn, leads to higher filtration and sedimentation efficiencies.

Coagulation can have a fundamental impact in the removal of pathogenic contaminants. In a particular

study, the removal of Cryptosporidium oocysts was increased from 1.5 log to 3.7-log by adding an

optimal concentration of coagulant (Dugan, et al., 2001). Furthermore, it was also shown that the

effectiveness of conventional treatment increased from 4.3 log to 5.8-log due to coagulant use (States,

et al., 2002). Last but not least, other authors suggest that the optimization of the coagulation process

for the reduction of turbidity also improves the removal of emerging pathogens (Xagoraki, et al., 2004).

Coagulation also has an impact on the removal of heavy metals and inorganic pollutants. The removal

efficiency of these compounds varies according to the type and amount of coagulant used. It is known

that ferric chloride has an overall higher efficiency in removing arsenic than aluminum sulfate, an

example of this is to be found in (Robert, et al., 1994). In this study, while ferric chlorite managed to

lower arsenic concentrations to under 0.5 μg/l by using a dosages of about 10 mg/l, aluminum sulfate

could not reach values under 0.5 μg/l even when using a dosage of 30 mg/l and having a more suitable

pH value. Ferric chloride, on the other hand, was also effective in reducing chromium concentrations

by 99% through a 1.7 mg/l dose (Lee & Hering, 2003).

The system that was considered for the coagulation cost analysis comprised of a dosing station that

included a 100 l tank, a dosing pump and a mechanical mixer. It should be noted that, although being a

fundamental part of a coagulation system, a flocculation tank was not included. This was decision was

made due to the fact that most of the coagulation systems that were found in scientific literature didn’t

include a flocculation tank. Table 4.7, displayed in the following page, shows the costs according to the

treatment capacity required and the type of coagulant used, while assuming a dosage of 20 mg/l of

coagulant.

26

Table 4.7 – Estimated cost for a coagulation water treatment system as a function of the type of coagulant used and treatment capacity

Coagulant Parameter Daily treatment capacity (m3)

15 50 100 200 300 450

Aluminum sulfate



Total O&M costs (k€) 3.3 3.6 3.9 4.6 5.2 6.3

Total AAC (k€) 6.1 6.3 6.8 7.4 8.2 9.7

Cost per m3 (€) 1.107 0.346 0.185 0.101 0.075 0.059

Ferric chloride



Total O&M costs (k€) 3.3 4.2 5.2 7.2 9.1 12.1

Total AAC (k€) 6.1 7.0 8.0 10.0 12.1 15.5

Cost per m3 (€) 1.107 0.382 0.221 0.137 0.110 0.094

4.4 Disinfection

4.4.1 Brief introduction and assumptions

Disinfection is a fundamental water treatment process through which bacterial and viral inactivation

occurs. Before proceeding into the different disinfection alternatives, it is important to make a brief

remark regarding their efficiencies. The efficiency of every alternative other than UV disinfection is often

measured by its CT value, which is simply a product of the concentration of a disinfectant reagent with

its contact time with the water being disinfected. This value greatly depends on the length of the water

distribution system and the existence of a reservoir downstream. Since both of these aspects would turn

the problem of evaluating costs more complex, they were disregarded and it was simply assumed that

the water treatment system has a reservoir immediately downstream that assures a contact time in the

range of hours.

4.4.2 Chlorination

4.4.2.1 Reaction, feeding methods and inactivation efficiency

Chlorination is a disinfection process in which chlorine is added to the water. When chlorine is added, it

reacts with water and forms both chlorine hydroxide (𝐻𝑂𝐶𝑙) and hydrochloridric acid (𝐻𝐶𝑙) according to

the following reaction:

HClHOClOHCl 22

Chlorine hydroxide and hydrochloridric acid are the main agents responsible for the inactivation of

bacteria and viruses. Both of these substances, although having different disinfecting capabilities, are

referred as free chlorine.

27

There are different means of adding free chlorine to water. The following ones were the ones taken into

account:

Chlorination through gaseous chlorine;

Chlorination through the use tablets of calcium hypochlorite;

Chlorination through a solution of sodium hypochlorite.

Before proceeding into the cost analysis of any of the chlorine feed alternatives, it was fundamental to

assess the chlorine dosages required. In order to do so, the efficiency of free chlorine was analyzed in

terms of CT requirements for different microorganisms through (Hoff, 1986). The results are shown in

the following Table 4.8.

Table 4.8 – Summary of free chlorine CT value ranges for 99% inactivation of various microorganisms at 5 ºC and a pH value between 6 and 7

Microorganism Free chlorine CT values (mg.min/l)

E.coli 0.034-0.05

Polio 1 1.2-2.5

Rotavirus 0.01-0.05

Bacteriophage f2 0.08-0.18

G. lamblia cysts 47 – 150 >

G. muris cysts 30-630

Adapted from (Hoff, 1986).

Based on engineering guideline values and on Table 4.8, it was assumed that a dosage of 0.5 mg/l

would be enough to reach disinfection efficiencies of at least 3-log for the contact time previously

assumed. The chlorination costs were also estimated for a dosage of 5 mg/l so that the increased costs

of higher dosages could be assessed.

4.4.2.2 Gaseous chlorine

Gaseous chlorine is the purest form of chlorine available. The feed system considered for the cost

estimation was a gaseous chlorine dosing pump attached to a chlorine gas cylinder. The gaseous

chlorine system estimated costs are shown in Table 4.9, which is displayed in the following page, for

both dosages just defined.

28

Table 4.9 – Estimated costs for a gaseous chlorine system as a function of the treatment capacity for different chlorine dosage

Chlorine dosage

Parameter Treatment capacity (m3)

15 50 100 200 300 450

0.5 mg/l



Total O&M costs (k€) 3.9 4.0 4.2 4.4 4.7 5.2

Total AAC (k€) 7.1 7.2 7.4 7.7 8.1 9.0

Cost per m3 (€) 1.295 0.394 0.204 0.105 0.074 0.055

5 mg/l

Total O&M costs (k€) 3.9 4.3 4.6 5.4 6.1 7.3

Total AAC (k€) 7.1 7.4 7.9 8.6 9.5 11.1

Cost per m3 (€) 1.295 0.407 0.217 0.118 0.087 0.068

Note: The useful life and capital costs are the same for both dosages.

4.4.2.3 Calcium hypochlorite tablets

When compared to gaseous chlorine, a calcium hypochlorite feed system is often viewed as a more

convenient solution due to the fact that it requires less safety measures. The system considered for the

cost estimation comprised of an automatic calcium hypochlorite chlorinator that required tablets as its

input. Its estimated costs are shown in the following Table 4.10 for chlorine dosages of 0.5 and 5 mg/l.

Table 4.10 – Estimated costs for a calcium hypochlorite tablets as a function of the treatment capacity

Chlorine dosage


15 50 100 200 300 450

0.5 mg/l



Total O&M costs (k€) 3.8 4.1 4.4 4.9 5.5 6.4

Total AAC (k€) 7.2 7.4 7.8 8.4 9.1 10.5

Cost per m3 (€) 1.313 0.406 0.214 0.115 0.083 0.064

5 mg/l

Total O&M costs (k€) 3.8 4.8 5.8 7.8 9.8 12.9

Total AAC (k€) 7.2 8.1 9.3 11.3 13.4 17.0

Cost per m3 (€) 1.313 0.445 0.254 0.154 0.123 0.103


4.4.2.4 Sodium hypochlorite solution

Sodium hypochlorite is available through two different alternatives, it can be either generated through

an onsite generator or it can be ordered in bulk using tank trucks. The former alternative is often

regarded as an economically viable disinfection solution due to the fact that it requires salt as its main

29

compound. However, the disinfection efficiency of this alternative is difficult to measure by virtue of the

uncertainty in the concentration of the disinfection products that result from the sodium hypochlorite

generation. As for the latter alternative, it is often viewed as an expensive solution that is non-viable for

small treatment systems with low yearly requirements of sodium hypochlorite. Therefore, only the costs

for the onsite generator alternative were estimated. The results are shown in the following Table 4.11

for the two chlorine dosages previously defined.

Table 4.11 – Estimated costs for a calcium hypochlorite solution system as a function of the treatment capacity

Chlorine dosage


15 50 100 200 300 450

0.5 mg/l



Total O&M costs (€k) 4.9 5.1 5.4 5.7 6.2 7.0

Total AAC (k€) 8.9 9.0 9.4 10.0 10.7 11.9

Cost per m3 (€) 1.618 0.495 0.258 0.137 0.097 0.073

5 mg/l

Total O&M costs k(€) 4.9 5.5 6.1 7.1 8.3 10.1

Total AAC (k€) 8.9 9.4 10.1 11.4 12.7 15.1

Cost per m3 (€) 1.618 0.514 0.277 0.156 0.116 0.092


4.4.3 Chloride dioxide

Chlorine dioxide, or 𝐶𝑙𝑂2, is a strong oxidative agent with the capability of inactivating microbiological

organisms and oxidizing inorganic compounds. Due to its versatility, chloride dioxide can be either

applied as pre-oxidant or as a primary disinfectant.

When compared with other disinfectants, chlorine dioxide is quite efficient and it also has the advantage

of not producing as many halogen compounds (Symons, et al., 1981). On the other hand, besides being

stable and capable of assuring a higher residual than chlorine, chlorine dioxide can achieve higher

disinfection efficiencies at higher pH values (Aieta & Berg, 1986). As in the case of free chlorine, its

efficiency was analyzed through its CT values, which were complied in Table 4.12, displayed in the

following page.

30

Table 4.12 – Summary of chlorine dioxide CT value ranges for 99% inactivation of various microorganisms at 5 ºC and a pH value between 6 and 7

Microorganism Chlorine dioxide CT values (mg.min/l)

E.coli 0.4 - 0.8

Polio 1 0.2 - 6.7

Rotavirus 0.2 - 2.1

Bacteriophage f2 -

G. lamblia cysts -

G. muris cysts 7.2 - 18.5


Through the comparison of both Table 4.8 and Table 4.12, it is possible to notice that chlorine dioxide

has higher CT values for E.coli than free chlorine. However, some authors affirm that chlorine dioxide

has in fact better biocidal capabilities than free chlorine (Aieta & Berg, 1986) (Hoff & Geldreich, 1981).

As a matter of fact, it was shown that a 3-log inactivation of E. coli was achieved by applying 0.16 mg/l

of chlorine dioxide at 15 ºC and at a pH of 7 (Scarpino, et al., 1979). Taking into account this result, it

was decided to use a rather conservative dosage of 0.5 mg/l for the chlorine dioxide disinfection system.

The chlorine dioxide system comprised of an automatic generation system that used Nadolyt, a 7.5%

𝑁𝑎𝐶𝑙𝑂2 solution, as its main input. The system’s cost estimation results are displayed in Table 4.13 for

different treatment capacities.

Table 4.13 – Estimated costs for a chlorine dioxide system as a function of the treatment capacity

Parameter Daily treatment capacity (m3)

15 50 100 200 300 450



Total O&M costs (k€) 4.6 4.9 5.4 6.2 7.2 8.5

Total AAC (k€) 10.0 10.4 10.9 11.8 12.9 14.8

Cost per m3 (€) 1.830 0.568 0.299 0.162 0.118 0.090

4.4.4 Chloramination

Chloramination is a disinfection process that relies on chloramines to inactivate bacteria and viruses.

Despite not being as efficient as chlorine in disinfection (Hoff & Geldreich, 1981), chloramines have the

advantage of being less reactive than their disinfection counterparts and allow for better residuals.

Hence why a chloramination process is not usually included in a treatment scheme as a primary

disinfection process but rather as a secondary one.

31

Chloramines are formed when chlorine hydroxide, or 𝐻𝑂𝐶𝑙, formed in the reaction of chlorine with water,

reacts with ammonia ( 𝑁𝐻3 ) or other chloroaminated compounds such as monochloramine or

dichloramine. The formation of chloramines is described by the following set of chemical reactions:

OHClNHHOClNH 223 (monochloroamine formation)

NH Cl HOCl NHCl H O2 2 2 (dichloroamine formation)

NHCl HOCl NCl H O2 3 2 (trichloroamine formation)

The extent to which each chloramine specie is formed depends on the pH value and the ratio between

free chlorine and ammonia. Despite being both dichloramine and trichloramine more efficient

disinfectants than monochloramine, the aim of the process is to produce a high concentration of this last

substance due to the fact that it is more adequate for secondary disinfection by virtue of its higher

chemical stability.

Before proceeding into the cost analysis, it’s important to understand the formation of chloramines in

order to dermine how much chlorine and ammonia is needed to disinfect the water. The first step in

assessing the amounts of reagents required lied in knowing how much free chlorine is susceptible of

reacting with ammonia when chlorine is added to the water. As it is possible to see in the following Table

4.14, when the pH is around 7, 𝐻𝑂𝐶𝑙 represents 75% percent of the free available chlorine (FAC) and

the hypochlorite ion (𝑂𝐶𝑙) represents the remaining 25%. Thus, only 75% of the chlorine that is added

to the water at a pH of 7 is actually capable of being involved in the reactions that form chloramines.

Table 4.14 – Percentage of hypochlorous acid in free chlorine as a function of pH

pH Percentage of 𝑯𝑶𝑪𝒍 present in FAC

6.0 97

7.0 75

7.2 63

7.5 49

7.6 39

7.8 28

8 3

Chloramine formation also depends on the chlorine to ammonia ratio. The following Figure 4.1 shows

the relationship between the chloramine species for different ratios of 𝐶𝐿2: 𝑁𝐻4 for a pH between 6.5

and 8. It is possible to observe that 𝑁𝐻2𝐶𝑙 is the only specie present for ratios up until 5:1. Thus, since

the main objective is to form 𝑁𝐻2𝐶𝑙, a value between 3:1 and 5:1 must be chosen.

32

Figure 4.1 – Chloramine formation as a function of 𝑪𝑳𝟐:𝑵𝑯𝟒 ratio for a pH between 6.5 and 8

Another particular factor that must be taken into account are the residual values of chloramines.

Engineering guidelines often stipulate a residual concentration between 2 and 3 mg/l. This range of

values was defined to take into account the main concern regarding the use of 𝑁𝐻2𝐶𝑙 which is its

nitrification by bacteria. In order to avoid this situation, a highly oxidative environment must be kept at

all times. It is known that the 𝑁𝐻2𝐶𝑙 concentration is correlated with how oxidative an environment is.

Figure 4.2 shows that concentrations above 2 mg/l of 𝑁𝐻2𝐶𝑙 are sufficient to keep a high enough

oxidative environment. Therefore, this value was defined as being a minimum residual value required.

Figure 4.2 – Bacterial growth according to the 𝑵𝑯𝟐𝑪𝒍 concentration

While taking into account everything that was evidenced, it was defined that the system would use a

𝐶𝐿2: 𝑁𝐻4 ratio of 4. To achieve this ratio, assuming that all of the 𝑁𝐻3 is in the ammonium state (𝑁𝐻4)

33

at pH levels lower than 7, it was defined that 4 mg/l of 𝐶𝐿2 and 0.75 mg/l of 𝑁𝐻3 were needed to be

added to the water. These concentrations, in turn, would form 3 mg/l of 𝑁𝐻2𝐶𝑙 and 1 mg/l of 𝑂𝐶𝑙. These

resulting concentrations, not only provide enough disinfection residuals but they are also expected to

lead to disinfection efficiencies of at least 3-log.

The process of chloramination requires two independent feed systems, one for chlorine and one for

ammonia. The feed systems for ammonia are similar to those ones described for chlorine during the

chlorination subchapter. Ammonia can be either added in a gaseous form (anhydrous ammonia) or in a

liquid form (aqueous ammonia).

Anhydrous ammonia is applied using an ammoniator. An ammoniator is a self-contained modular unit

with a pressure reducing valve, a gas flow meter and a feed rate control valve for controlling the flow of

ammonia. Anhydrous ammonia can be applied through either a direct type of feed or through a solution

feed. However, it is known that the direct feed method is the most adequate for small systems due to

the fact that these have process streams with low pressures and ammonia feed rates lower than 450 kg

per day (Dennis, et al., 1991).

As for aqueous ammonia, although it can either be produced by dissolving anhydrous ammonia into

deionized water or by ordering tank trucks or polyethylene lined steel drums, only the polyethylene lined

steel drums alternative was chosen to be analyzed. The reason behind this resides in fact that dissolving

anhydrous ammonia before adding it is obviously more expensive than simply adding it to the water. On

the other hand, similarly to the hypochlorite solution alternative, it was assumed that tank trucks are less

economically viable than using drums.

Regarding the chlorine feed system, with the aim of reducing overall costs, only the cheapest chlorine

feed alternative was chosen. Through the comparison of the estimated costs of the different chlorination

alternatives, it is possible to observe that gaseous chlorine is the cheapest one.

Taking into account everything that was evidenced and assumed throughout this subchapter, the

estimated costs of a chloramination system using a gaseous chlorine feed system together with either

an anhydrous or aqueous ammonia feed system were calculated and compiled in Table 4.15, which is

displayed in the following page.

34

Table 4.15 – Estimated costs for a gaseous chlorine feed chloramination system as a function of treatment capacity

Ammonia feed method Parameter

Treatment capacity (m3)

15 50 100 200 300 450

Anhydrous ammonia



Total O&M costs (k€) 3.7 4.1 4.6 5.6 6.7 7.6

Total AAC (k€) 7.5 7.8 8.4 9.4 10.7 12.1

Cost per m3 (€) 1.367 0.430 0.231 0.129 0.098 0.074

Aqueous ammonia hydroxide



Total O&M costs (k€) 4.2 5.0 5.8 7.3 8.8 11.2

Total AAC (k€) 7.6 8.3 9.2 10.7 12.4 15.2

Cost per m3 (€) 1.388 0.456 0.252 0.147 0.113 0.092

4.4.5 Ozonization

Ozone is one of the strongest disinfectants and oxidants available in water treatment. It has a biocidal

effectiveness ranked higher than any other disinfection reagent previously mentioned (Hoff & Geldreich,

1981). Its CT values for 99% inactivation of various microorganisms are shown in the Table 4.16, which

is displayed in the following page.

35

Through the comparison of Table 4.16 with Table 4.8 it is possible to observe that ozone has a CT value

for E.coli that is less than half of the CT value for free chlorine. Therefore, even though ozone has a

half-life of about 30 min, it was assumed that a dosage of 0.25 mg/l of ozone would be more than enough

to achieve a disinfection efficiency of at least 3-log.

It is known that ozone can be produced onsite by using an ozone generator that can requires either

dried air or liquid oxygen. Regarding this aspect, the assumption was made that the system used for the

cost estimation was the one that used dried air as its input. Its resulting estimated costs are shown in

the following Table 4.17 for 0.25 and 1 mg/l dosages.

Table 4.17 – Estimated costs for an ozone generator system as a function of treatment capacity

Ozone dosage


15 50 100 200 300 450

0.25 mg/l



Total O&M costs (k€) 2.8 2.9 3.0 3.1 3.5 3.8

Total AAC (k€) 5.4 5.5 5.7 6.0 6.7 7.5

Cost per m3 (€) 0.993 0.302 0.157 0.082 0.061 0.046

1 mg/l

Total O&M costs (k€) 3.1 3.1 3.3 3.2 3.9 4.1

Total AAC (k€) 6.5 6.5 6.8 7.0 8.9 9.6

Cost per m3 (€) 1.181 0.358 0.186 0.096 0.081 0.058


4.4.6 Ultraviolet disinfection

Ultraviolet disinfection is the process through which the inactivation of microorganisms occurs due to

the incidence of ultraviolet radiation that damages their DNA and hinters their reproduction.

UV disinfection, besides not producing toxic compounds and relying solely on energy as its input, is

known to be easy to install and to operate. This process, however, besides not providing any residual

Table 4.16 – Summary of ozone CT value ranges for 99% inactivation of various microorganisms at 5 ºC and a pH between 6 and 7

Microorganism Ozone CT values (mg.min/l)

E.coli 0.02

Polio 1 0.1-0.2

Rotavirus 0.006-0.06

Bacteriophage f2 -

G. lamblia cysts 0.5-0.6

G. muris cysts 1.8-2.0


36

treatment to the water, due to the fact that high contents of suspended soils hinder the disinfection

efficiency through the blocking of the irradiation of bacterial and viral cells, is only applicable to waters

with low levels of turbidity.

The efficiency of this process depends on the amount of energy that is irradiated by the lamp and

absorbed by the microorganisms. Although this energy can be irradiated using different wave lengths

ranging from about 40 to 400 nm, it is known that the most effective range is the 200-310 nm range and

that the inactivation effectiveness reaches its maximum at around 265 nm. Also, different lamps have

different spectrums of emission. Since mercury lamps have most of their emission spectrum in the range

of 250-270 nm, they are the most commonly used in the process of UV disinfection. The UV dosages

required for different disinfection efficiencies of pathogenic bacteria were widely studied throughout the

scientific literature and some of the results of different authors for the inactivation of E.coli and fecal

Streptococci are compiled in the following Table 4.18.

Table 4.18 – UV dosage required for different disinfection efficiencies of pathogenic bacteria

Microorganism UV Dose (mJ/cm2) / inactivation required

Source 1-log 2-log 3-log 4-log

Escherichia coli 2.5 3 3.5 5 (Harris, et al., 1987)

Escherichia coli 3 4.8 6.7 8.4 (Chang, et al., 1985)

Escherichia coli 4 5.3 6.4 7.3 (Sommer, et al., 1998)

Streptococcus faecalis 6.6 8.8 9.9 11 (Chang, et al., 1985)

Streptococcus faecalis 5.5 6.5 8 9 (Harris, et al., 1987)

Commercial UV reactors that are available in the market usually have a UV dose between 40 and

60 mJ/cm2 and most manufacturers claim that this dose is enough to reach inactivation efficiencies of

4-log. This claim is indeed supported by Table 4.18 and higher inactivation efficiencies might even be

probably achieved. The estimated costs for the UV disinfection system are compiled in Table 4.19.

Table 4.19 – Estimated costs for an UV disinfection system as a function of treatment capacity

Parameters Daily treatment capacity (m3)

15 50 100 200 300 450



Total O&M costs (k€) 4.1 4.2 4.5 5.2 6.0 7.1

Total AAC (k€) 7.5 7.7 8.0 9.1 10.4 12.1

Cost per m3 (€) 1.376 0.421 0.220 0.124 0.095 0.073

37

4.5 Water stabilization

When the water leaves the water treatment system it is fundamental that it is stable, otherwise, some

problems such as pipe corrosion or scaling can impair the treatment operation and diminish the water

quality.

Water stabilization can be achieved through the concept of calco-carbonic equilibrium. This equilibrium

is achieved when the water is neither aggressive nor has the tendency of depositing calcium carbonate

(𝐶𝑎𝐶𝑂3) on the surface of the piping system.

In the water stabilization process, if the water is aggressive, calcium hydroxide (𝐶𝑎𝑂) should be added.

If, on the other hand, the water has high tendency of depositing a layer of calcium carbonate, it must be

either aerated or filtrated through a RO membrane or an cationic resin.

It was assumed that if the water required aeration, a PTA or MSBA treatment process would be enough

to aerate the water to a level of equilibrium. As for aggressive water, in order to evaluate its costs, the

Hallopeau & Dubin method was used. It was assumed that the aggressive water that enters the

treatment plant has an expected pH between 6.5 and 7.5 pH and a relatively low alkalinity value of 20

mg/l of CaO. Taking into consideration these values, it was defined that the amount of lime required to

reach the equilibrium was somewhere between 5 and 25 mg/l.

The system that was considered in the cost analysis is similar to the one considered for coagulation.

The calculated costs for lime dosages of 5 and 25 mg/l are shown in the following Table 4.20.

Table 4.20 – Estimated costs for a water stabilization system as a function of treatment capacity

Lime dosage Parameters Daily treatment capacity (m3)

15 50 100 200 300 450

5 mg/l



Total O&M costs (k€) 3.9 4.1 4.4 4.9 5.4 6.2

Total AAC (k€) 7.3 7.5 7.9 8.4 9.1 10.4

Cost per m3 (€) 1.339 0.411 0.216 0.115 0.083 0.063

25 mg/l

Total O&M costs (k€) 3.9 4.3 4.7 5.4 6.2 7.4

Total AAC (k€) 7.3 7.6 8.2 9.0 9.9 11.6

Cost per m3 (€) 1.339 0.419 0.224 0.123 0.090 0.071


38

4.6 Filtration

4.6.1 Rapid sand pressure filtration

Filtration is a fundamental process in water treatment. This process consists of the physical removal of

the suspended solids in the water as the result of their passage through a permeable and porous

material that is capable of retaining them.

Sand filtration methods distinguish themselves from other types of filtration methods by having a

complementary biological treatment that develops throughout time at the surface layer of their sand

media. This developed layer is called schmutzdecke which is an accumulation of organic and inorganic

debris in which biological activity is stimulated.

Rapid sand filtration is one of the most commonly used sand filtration methods in small scaled water

treatment systems. Similarly to the adsorption process, rapid sand filtration might be operated either

under pressure through the use of pressure vessels or due to gravity in concrete basins. Once again,

due to its high investment costs (EPA, 1977), the conventional alternative of using concrete basins was

disregarded.

Rapid sand filtration can be used to filter pathogenic microorganisms and heavy metals. In terms of

microbiological removal efficiencies, it was shown that this filtration method is capable of achieving

efficiencies of about 3-log for both Cryptosporidium and Giardia when a dose of 10 mg/l of aluminum

sulfate is used in coagulation (Ongerth & Pecoraro, 1995). Furthermore, in a properly operated treatment

plant producing water with a turbidity between 0.1-0.2 NTU, a 3-log removal was achieved for Giardia

cysts (Nieminski & Ongerth, 1995). These efficiencies, however, since the treatment requirements

established in chapter 2 measure the microbiological contamination in terms of E.coli bacteria or fecal

Streptococci, which are relatively smaller than Cryptosporidium and Giardia, should be considered with

some precaution. Last but not least, it is also known that the removal efficiency of microorganisms

doesn’t depend on configuration of the filtration media chosen (Swertfeger, et al., 1999).

As for the removal of heavy metals and inorganic compounds, a removal efficiency between 60 and

90% is expected. One particular report demonstrated that removal efficiencies of about 70% for total

arsenic and 90% for total iron were achieved while using rapid sand filtration (Shiao, et al., 2007).

Another similar report not only evidenced a removal efficiency of 50% for total arsenic and above 90%

for total iron, but also showed that, without a proper pre-oxidation stage, rapid sand filtration for arsenic

removal might be useless (Valigore, et al., 2007). Finally, (Condit & Chen, 2006) evidenced the

fundamental role of ferric chloride coagulation in arsenic removal by improving a removal efficiency of

60% for total arsenic to a value between 80 to 90%.

Without further ado, the estimated costs for the rapid sand pressure filtration system are compiled in

Table 4.21, which is displayed in the following page.

39

Table 4.21 – Estimated costs for a rapid sand pressure filtration system as a function of treatment capacity


15 50 100 200 300 450



Total O&M costs (k€) 5.5 5.7 6.0 6.6 7.3 9.4

Total AAC (k€) 9.7 9.9 10.6 11.4 12.9 17.2

Cost per m3 (€) 1.780 0.542 0.289 0.156 0.118 0.105

4.6.2 Slow sand filtration

Slow sand filtration was the first type of porous media filtration process used in water treatment. As its

name implies, this filtration process it is accomplished by passing the water at a relatively low rate

through a sand medium. Similarly to rapid sand filtration, it complements its primary treatment through

the schmutzdecke that is developed throughout time at the surface layer.

The microbiological removal by slow sand filtration of E.coli, under different filtration conditions, was

shown to be somewhere 0 and 3-log (Unger & Collins, 2008). Other efficiency removals regarding other

parameters are shown in the following Table 4.22.

Table 4.22 – Typical treatment performance of conventional slow sand filters

Water quality parameter Treatment performance or reduction capacity

Turbidity < 1.0 NTU

Coliforms 1 to 3-log units

Enteric viruses 2 to 4-log units

Giardia cysts 2 to 4+ log units

Trihalomethane precursors < 25%

Adapted from (McGraw-Hill, 2005)

Regarding the slow filtration system design assumptions and the resultant estimated costs, these are

shown in the following page as Table 4.23 and Table 4.24, respectively.

40

Table 4.23 – Slow filtration system design assumptions

Design assumption Value

Filtration rate 0.15 m/h

Freeboard 0.6 m

Water height above the media 2 m

Sand depth 0.6 m

Gravel depth 0.5 m

Lower concrete slab thickness 0.5 m

Later concrete wall thickness 0.3 m

Escavation slope (V:H) 2:1

Spacing between pipes 0.5 m

Schmutzdecke cleaning frequency Once every 180 days

Table 4.24 – Estimated costs for a slow sand filtration system cost as a function of treatment capacity


15 50 100 200 300 450



Total O&M costs (k€) 3.9 4.9 6.3 8.7 11.3 15.4

Total AAC (k€) 8.2 12.1 17.1 26.1 36.0 51.7

Cost per m3 (€) 1.506 0.661 0.469 0.357 0.329 0.315

4.6.3 Diatomaceous earth filtration

The process of diatomaceous earth filtration, or DE filtration, uses diatomic earth as its filtrating media.

This earth has a size range between 5 and 100 μm and is 85% made out of silica, which is a material

with a high chemical stability and good permeability.

The process of DE filtration is divided into three distinct phases. In the first phase, called DE pre-coating,

a solution containing the filtering media is pumped through the filtration vessel. This filtration vessel

contains septums that block the flow of the filtrating media and, consequently, form a layer of it. This

process lasts until the layer reaches a 3 mm thickness. The second phase of the process is the operation

of the DE filter. Throughout this phase, the influent water is filtered until there is a considerable reduction

of the filtration rate due to the loss of hydraulic load that occurs because of the progressive clogging of

the filter. Finally, at the third phase, the direction of the flow is inverted in order to wash away the clogged

media and to prepare the vessel for another filtration cycle.

Among the different factors that influence the efficiency of DE filtration, the most important one is the

grade of the DE used (Lange, et al., 1986). DE is graded according to its median particle size. The

41

median size of the grades used in water treatment often range from 15 to 30 μm. As it was shown in

(Lange, et al., 1986), although any grade size is capable of achieving reasonably high removal

efficiencies for Giardia cysts (about 2-4-log), only the grades with a median size of 15 μm or less were

capable of efficiently removing coliform bacteria (2-3-log) under different circumstances. Furthermore,

it was also shown that the turbidity removal efficiency seems to be very low for this kind of treatment

process, and a turbidity removal of 1-log was only achieved by high-grade diatomaceous earths with

very low median sizes.

As for the removal efficiency of viruses, it was shown that DE filtration is capable of achieving 1-log

removal efficiencies of Escherichia coli T2 bacteriophages when the DE is coated with a filter aids such

as ferric hydrates or polyelectrolytes (Brown, et al., 1974a) (Brown, et al., 1974b). Otherwise, the

removal efficiency of viruses measured stayed below 1-log.

As for the removal efficiencies for inorganic pollutants, it was found that DE filtration is efficient in

removing iron and manganese (Coogan, 1962) (Velde, et al., 1962).

The cost estimations for the DE filtration system as a function of the treatment capacity and for two

different backwash frequencies are shown in the following Table 4.25.

Table 4.25 – Estimated costs of a DE filtration system as a function of the treatment capacity

Backwash frequency


15 50 100 200 300 450

Once per week



Total O&M costs (k€) 5.1 7.0 7.2 9.5 12.0 14.6

Total AAC (k€) 9.1 11.6 11.7 14.8 18.5 22.3

Cost per m3 (€) 1.664 0.635 0.321 0.203 0.169 0.136

7 times per week

Total O&M costs (k€) 6.7 19.3 19.5 34.3 49.0 64.0

Total AAC (k€) 10.7 23.9 24.1 39.5 55.6 71.7

Cost per m3 (€) 1.946 1.312 0.659 0.542 0.507 0.437

Note: The useful life and capital costs are the same for both frequencies.

4.6.4 Bag and cartridge filtration

Bag and cartridge filtration belong to the group of pressure filtration processes. In the case of bag

filtration systems, influent water passes through a bag-shaped filtration unit where the particles are

retained by the bag's filter media. These bags are available with different pore size widths ranging from

1 to 200 μm. As for cartridge filtration, it typically includes pressure filters with pleated fabrics,

membranes or strings wrapped around a filter element and housed in a pressure vessel. This pleating

allows for a higher surface area when compared with bag filtration, which makes these kind of filters last

longer. Similarly to bag filters, cartridge filters are available with different pore size width ranging from 1

to 100 μm.

42

The efficiency of bag and cartridge filtration depends on the width of the membrane pore. Theoretically

all the particles whose size is larger than the membrane’s pore width should be intercepted by the

membrane, but, in reality, this doesn’t happen due to factors such as temperature and bacteria pliability.

In the following Figure 4.3, the contaminants that are covered by bag and cartridge filtration pore sizes

as well as the distribution of other common contaminants and filtration technologies are shown.

Figure 4.3 – Particle size distribution of common contaminants and associated filtration

technology

Figure taken from (EPA, 2001).

From observing Figure 4.3, it is possible to conclude that, although being suitable for the removal of a

wide range of bacteria, due to the fact that they are not capable of intercepting viruses, bag and cartridge

filtration require a post-disinfection process.

EPA tested bag and cartridge filtration for surface water with turbidity values ranging from 1 to 10 NTU

and with an average particle size between 1 and 3 μm (EPA, 2003). Disregarding initial NTU values,

although their life expectancy varied greatly, any type of filter was capable of lowering turbidity to values

lower than 0.5 NTU. Furthermore, Cryptosporidium removal efficiencies were also tested and EPA

estimated removals between 1 and 2-log.

Similarly to what was mentioned earlier for the rapid sand filtration process, due to the fact that the

pathogenic parameters that were established back in chapter 2 measure water quality in terms of

coliform bacteria and fecal Streptococci, which are relatively smaller than Cryptosporidium, the expected

removal efficiencies are smaller than the ones measured by EPA. If an analogy between the size of

coliform bacteria, fecal Streptococci and the average particle size is established, then the expected

efficiency should be somewhere around 70 and 80%, which was the efficiency measured by EPA for

the turbidity removal.

As for the types of filtration systems considered in the cost analysis, in the case of bag filtration, single

bag carbon steel housing were chosen alongside with high flow bags. For the cartridge filtration system,

43

a multi-cartridge carbon steel housing with different cartridge capacities was chosen according to the

flow required.

Regarding the bag and cartridge replacement frequency, it was assumed that, while filtration bags would

be replaced daily, cartridge filters would be replaced once every 45 days by virtue of their higher surface

filtration area. Without further ado, the cost estimations for bag and cartridge filtration systems are

displayed in the following Table 4.26.

Table 4.26 – Estimated costs for a bag and cartridge systems as a function of treatment capacity

Filtration system


15 50 100 200 300 450

Bag filtration



Total O&M costs (k€) 11.5 11.7 11.9 12.3 12.7 13.3

Total AAC (k€) 14.5 14.8 15.2 15.7 16.3 17.2

Cost per m3 (€) 2.654 0.810 0.417 0.215 0.149 0.105

Cartridge filtration



Total O&M costs (k€) 5.0 5.8 7.2 8.7 10.2 13.1

Total AAC (k€) 10.1 11.1 12.7 14.2 16.2 19.8

Cost per m3 (€) 1.838 0.610 0.347 0.195 0.148 0.121

4.6.5 Membrane filtration

Membrane filtration includes micro and ultrafiltration. These processes, much like bag and cartridge

filtration, use membranes that act as sieves. The main difference between membrane filtration and bag

and cartridge filtration resides in the pore width of their membranes. As it can be seen in Figure 4.3, the

pore size range for membrane filtration is much lower and their size ranges from 0.001 to 1 μm.

It’s important to refer that both nanofiltration and reverse osmosis could have been included in this

subchapter, but it was decided to include both of them in the membrane separation subchapter by virtue

of their different operating conditions. These two processes, besides being capable of intercepting

contaminants that are dissolved in water down to the molecular level, require a reasonably higher

working pressure (between 50 and 600 psi) when compared with bag, cartridge and membrane

processes.

In order to ascertain their bacterial and turbidity removal efficiency, EPA tested micro and ultrafiltration

under similar conditions as those ones under which the tests on bag and cartridge filters were performed

(EPA, 2003). The results of the tests have shown that both micro and ultrafiltration membranes

demonstrated turbidity removal efficiencies between 90 and 98%.

44

As for the removal of pathogenic microorganisms, while microfiltration achieved removal efficiencies of

3 to 4-log for Cryptosporidium, ultrafiltration not only intercepted Cryptosporidium with efficiencies

between 3 and 5-log, but also managed to filter viruses with recorded removal efficiencies of 4-log for

MS2 Bacteriophages.

Before presenting the cost estimation for membrane filtration, it should be noted that, due to the fact

that the influent water must have some kind of pretreatment before being filtered by micro and ultra-

membranes, the costs of using this kind of system are expected to be higher than the ones estimated.

It is known that micro and ultrafiltration membranes can clog and rupture quickly if they are used to filter

coarse materials that may be removed using cheaper filtration methods such as rapid sand filtration or

bag and cartridge filtration. The fact that a bag/cartridge system costs only a couple thousand of euros

compensates the cost of a membrane filtration system which is usually in the tens of thousands of euros

(EPA, 2003). The estimated costs for a membrane filtration system are shown in the following Table

4.27.

Table 4.27 – Estimated costs for both micro and ultrafiltration system as a function of treatment capacity


15 50 100 200 300 450



Total O&M costs (k€) 3.6 4.2 5.0 6.4 7.9 10.5

Total AAC (k€) 6.7 7.6 8.6 10.9 13.7 18.1

Cost per m3 (€) 1.218 0.418 0.237 0.149 0.125 0.110

Note: Since membrane manufacturers don’t distinguish micro from ultrafiltration membranes, the price difference between

both types of membranes was disregarded and the costs were calculated for a membrane that most closely resembles a

ultrafiltration membrane.

4.7 Ion exchange

4.7.1 Brief introduction

The ion exchange process, as the name suggests, consist in the removal of unwanted ions from the

water through reversible chemical reactions. The removal of ionic substances occurs when the water

flows through a media that is made of an artificial resin that has the capability of adsorbing those

substances. This resin can be either cationic or anionic. While a cationic resin adsorbs cations, a anionic

resin adsorbs anions. These resins can also be divided into strong and weak base resins according to

their degree of ionization.

The ion exchange process is slightly different from other types of media filtration processes. In the

beginning of a filtration cycle, the resin is saturated with exchange ions. As water flows through the

45

media, ion exchanges occurs and the media starts progressing towards a state of equilibrium in which

there are no ionic exchanges. When this state is reached, it is necessary to establish the initial condition

by back washing the media and subsequently rinsing it with a solution that has a high concentration of

ions capable of removing those ones adsorbed by the resin. After the backwash and the media rinsing,

the cycle is complete and the process can start all over again.

Ion exchange has a huge application in the removal of heavy metals and inorganic substances. While

cation exchange is mainly used to soften water, it is known that anion exchange is used to remove

nitrates, arsenate and bromates. In fact, an arsenic removal efficiency above 90% was achieved by

using ion exchange (Wang, et al., 2002). Nonetheless, the effectiveness of both types of ion exchange

must be carefully evaluated according to the affinity that different resins have towards different ions.

For instance, due to the different anionic substances that have a higher affinity towards an anionic resin,

most of these resins are incapable of effectively remove fluoride from water (Mahmood, et al., 2007).

4.7.2 Cation exchange

Before estimating the cost of a cation exchange system, some design specifications, such as the type

of resin, rinsing solution used and the target pollutant, must be defined. The definition of the resin and

rinsing solution is required to know the operation capacity of the resin in terms of eq/l. Once this capacity

is known, by considering the concentration of a target pollutant in water and its eq/l value, it is possible

to assess other operational design requirements such as the backwash frequency.

The chosen resin was a 𝑁𝑎+ form 8% cross-linked divinylbenzene sulfonic acid resin. This resin was

chosen due to the fact that, since it is in 𝑁𝑎+ form, a cheap and rinsing solution such 𝑁𝑎𝐶𝑙 could be

applied in its regeneration process. Figure 4.4, presented in the following page, shows the ion exchange

operating capacity as a function of the 𝑁𝑎𝐶𝑙 regenerant level for the 8% polystyrene-divinylbenzene

matrix using 𝑁𝑎𝐶𝑙 as the rinsing solution.

46

Figure 4.4 – Sulfonic acid resin operating capacity vs. regenerant level for sodium-cycle operation

Taken from Dowex Ion Exchange Resins – Fundalmentals of Ion Exchange

It was assumed that the regenerant level would be 100 g/l of 𝑁𝑎𝐶𝑙. According to Figure 4.4., an operation

capacity of about 25 kgr/ft3 (0.88 kgr/l) corresponds to this level of regenerant.

Regarding the targeted cations, since cation exchange has the capacity of adsorbing different types of

them, it would be necessary to analyze the whole range of the cations that are expected to occur in the

water in order to determine the number of bed loads required before a backwash. However, since in

water treatment the most restricting cations are 𝑀𝑔2+ and 𝐶𝑎2+ due to their low equivalent mass and

high concentration in water when compared with other ions, this was not necessary. Both of these ions

are closely related to water hardness and it is known that water has hardness values ranging from

0.26 to 2.78 gr/l. Based on these values and the operating capacity previously defined, a sodium chloride

rinsing is required after the flow of 300-3,400 liters of water per liter of resin.

Taking into account everything that was just mentioned, and assuming a pressure vessel system as the

one used for rapid sand filtration, the cost estimations for the cation exchange process were calculated

and compiled in Table 4.28, which is dispayed in the following page, for waters with hardness

concentrations of both 0.5 gr/l and 2 gr/l.

47

Table 4.28 – Estimated costs for a cation exchange systems as a function of treatment capacity for different hardness concentrations

Hardness concentration


15 50 100 200 300 450

0.5 gr/l



Total O&M costs (k€) 6.1 6.4 6.2 7.8 8.8 13.1

Total AAC (k€) 11.4 11.7 11.3 13.6 15.4 22.1

Cost per m3 (€) 2.078 0.640 0.310 0.187 0.141 0.135

2 gr/l

Total O&M costs (k€) 6.3 7.1 12.6 10.5 12.8 25.1

Total AAC (k€) 11.6 12.3 0.0 16.3 19.4 34.1

Cost per m3 (€) 2.115 0.676 0.368 0.223 0.178 0.207

Note: The useful life and capital costs are the same for both hardness concentrations.

4.7.3 Anion exchange

As for the ionic resin, the chosen matrix was the same as the one chosen for cation exchange, the only

difference resides in the resin form, which, instead of being in a 𝑁𝑎+ form, is in a 𝐶𝑙− form.

Based on catalogues of different anionic resin manufacturers, it was possible to conclude that the total

capacity of a anionic resin is usually half of the cationic ones. Therefore, it was assumed that, while

cationic resins often have total capacities of about 2 eq/l, or about 50 kgr/l, anionic resins have capacities

of about 25 kgr/l. Additionally, since the operating capacity of the anionic resin used was unknown, it

was also assumed that this capacity was about half of the total capacity for the same regenerant

concentration chosen for the cationic resin. This assumption was based on the fact that cationic resins

also have operating capacities that are about half of their total capacity. Based on these assumptions,

it was assumed that the choosen anionic resin has an expected operation capacity of about 12.5 kgr/l.

Regarding the rinsing frequency, a similar approach was adopted as the one used for the cationic

exchange cost estimation. Among the anions that are included in Table 2.3, the ones that were

considered in the estimation of the system’s cost were the nitrates due to their high occurrence

concentration (100-300 mg/l) and low equivalent mass. Also, since anionic exchange is a process often

used to remove heavy metals such as arsenic, this pollutant was also considered in its arsenate form,

or As(III), with a concentration of 100 μg/l.

The costs estimations for the anionic exchange process were compiled in the following page in Table

4.29. This table shows the estimated costs for the removal of nitrate at A1 and A3 concentrations and

for the removal of arsenate at a A3 concentration.

48

Table 4.29 – Estimated costs for an anion exchange systems as a function of treatment capacity for arsenate and different nitrate concentration

Pollutant concentration


15 50 100 200 300 450

100 mg/L nitrate



Total O&M costs (k€) 6.1 6.5 6.4 8.2 9.4 14.8

Total AAC (k€) 11.3 11.7 11.5 13.9 15.9 23.7

Cost per m3 (€) 2.067 0.640 0.314 0.191 0.145 0.144

300 mg/L nitrate

Total O&M costs (k€) 6.3 7.1 7.7 10.7 13.2 26.1

Total AAC (k€) 11.5 12.3 12.7 16.5 19.7 35.0

Cost per m3 (€) 2.102 0.675 0.348 0.225 0.180 0.213

100 μg/L arsenate

Total O&M costs (k€) 6.0 6.2 5.8 7.0 7.5 9.1

Total AAC (k€) 11.2 11.4 10.8 12.7 14.0 18.0

Cost per m3 (€) 2.050 0.623 0.297 0.174 0.128 0.110

Note: The useful life and capital costs are the same for every pollutant.

4.8 Membrane separation

Membrane separation processes, such as nanofiltration (NF) and reverse osmosis (RO), are capable of

virtually removing any kind of pollutant with high efficiencies.

Both NF and RO operate using the principle of osmosis, which is the natural flow of a solvent through a

semi-permeable membrane from a less to a more concentrated solution. The concentration difference

between these solutions induces a pressure differential called the osmotic pressure. Reverse osmosis

consists simply in the reversal of the osmotic process by applying pressure in excess to this osmotic

pressure. The differences between both processes lie in their different molecular cut-off weight ranges

and the range of pressures used to counteract the established osmotic pressures.

Regarding their pathogenic microorganism removal efficiencies, it was shown that NF and RO have the

capability of achieving very high removal efficiencies. In the case of bacteria, both processes

achieved 4-log removals for microspheres, which have a size much inferior when compared to fecal

Streptococci and coliform bacteria (Kitis, et al., 2003). As for viruses, while NF achieved efficiencies

between 3 and 4-log for the removal of the MS2 bacteriophage virus, RO achieved efficiencies between

5 and 6-log (NSF International, EPA, 2006).

These membranes were also tested for their removal efficiencies of both organic and inorganic

substances and ionic species. It is known that the ionic species are strongly correlated with the water’s

conductivity and it was shown that the removal of conductivity for these membranes was of

about 2-log (Kitis, et al., 2003) (NSF International, EPA, 2006) (Waypa, et al., 1997). As for the removal

of inorganic substances, it was shown that removal efficiencies between 1 and 2-log were achieved by

49

both NF and RO (Waypa, et al., 1997). In another particular study, RO membranes also achieved

removal efficiencies of about 2-log in the removal of both organic and inorganic substances.

In what concerns the design of both membrane systems, while typical filtration modules with permeate

flow capacities ranging from 3 to 15 m3/h were chosen for the NF system, low pressure membranes with

flow capacities of about 2 m3/h were chosen for the RO system. Also, it was assumed that the operating

pressure was of 110 psi for both processes and the design flow was multiplied by 1.25 in order to take

into account an assumed permeate flow of 80% for both types of membranes. The costs of

the NF and RO membrane systems are compiled in the following Table 4.30.

Table 4.30 – Estimated costs for both NF and RO filtration systems as a function of treatment capacity

Filtration system


15 50 100 200 300 450

NF



Total O&M costs (k€) 5.1 6.7 6.8 9.2 10.6 13.7

Total AAC (k€) 8.6 10.4 10.8 13.9 16.6 21.7

Cost per m3 (€) 1.566 0.569 0.295 0.191 0.151 0.132

RO



Total O&M costs (k€) 5.0 6.1 7.9 11.3 14.8 20.0

Total AAC (k€) 8.4 10.1 12.8 18.5 24.6 33.8

Cost per m3 (€) 1.526 0.552 0.350 0.254 0.224 0.206

Note: These costs should not be directly compared with other filtration alternatives because the use of either NF or RO imply

the existence of other pretreatment processes in order to avoid quick membrane clogging.

4.9 Oxidation

The process of oxidation aims at removing undesirable tastes and odors and aiding in the removal of

inorganic substances. Oxidation can be achieved either through water aeration or through the addition

of chemicals. Oxidation through water aeration, although being quite efficient in precipitating soluble iron

in water, has limited application. In fact, it was shown that different aeration methods, including those

presented in back in subchapter 4.1, have little or no impact in the oxidation of arsenate or manganese

(Lowry & Lowry, 2002). Chemical oxidation, on the contrary, has relatively higher oxidation efficiencies

and by virtue of these, water aeration will be disregarded in the cost estimation of the oxidation process.

Some of the available chemical oxidants, such as ozone, chlorine or chlorine dioxide, were already

analyzed in the disinfection subchapter and if the dose that was earlier assumed in these processes

doesn’t change, the costs should be reasonably the same as the ones estimated for disinfection. In

order to assess the required dosages for the oxidants, the stoichiometric value of their reduction

reactions with typical reductants, such as As(III), Fe(II) and Mn(II), were surveyed. These values were

50

also surveyed for the potassium permanganate, which is a commonly used oxidant. The stoichiometric

values and the doses required are shown in the following Table 4.31.

Table 4.31 – Doses required according to each oxidizing agent for the reduction of As(III), Fe(II) and Mn(II)

Oxidizing agent Reductant Stoichiometric value Dose

required1,2(μg/l)

Ozone

As(III)

0.64 12.8-64

Potassium permanganate 1.06 21.2-106

Chlorine 0.95 19-95

Chlorine dioxide 1.80 36-180

Monochloroamine 0.69 13.8-69

Ozone

Fe(II)

0.43 860

Potassium permanganate 0.71 1420

Chlorine 0.64 1280

Chlorine dioxide 0.24 480

Monochloroamine 0.46 920

Ozone

Mn(II)

0.88 440

Potassium permanganate 1.44 720

Chlorine 1.29 645

Chlorine dioxide 2.45 1225

Monochloroamine 0.94 470

1. The range of values for the dosage required for the arsenic oxidation was calculated by multiplying the values of the A1 and

A3 classes corresponding to arsenic by the stoichiometric value.

2. The dosage required for Fe(II) and Mn(II) oxidation was calculated considering a concentration of 2 mg/L of Fe(II) and 0.5

mg/L of Mn(II).

By looking at Table 4.31 it is possible to ascertain that the dosages that are required during oxidation

are much high than the ones required for disinfection and, on the other hand, it is also possible to notice

that since both Fe(II) and Mn(II) occur in much higher concentrations in water, arsenic doesn’t have

much relevance in determining the dose necessary.

Ozone, whose feed system was analyzed while considering a dosage of 0.25 mg/l in the disinfection

subchapter, requires a dosage of about 1.3 mg/l if arsenic, iron and manganese are in concentrations

of 100, 2000 and 500 μg/l respectively. As for chlorine dioxide, the dosage required under the same

conditions is 1.7 mg/l , more than 3 times higher than its disinfection dose. Last but not least, the dosage

required of potassium permanganate is of about 2.3 mg/l.

Regarding the oxidation efficiency of the mentioned oxidants, it was shown that, with such stoichiometric

values, chlorine, potassium permanganate and ozone, when in the absence of interfering reductants,

were capable of quickly oxidizing more than 95% of arsenic (Ghurye & Clifford, 2001). In the same study,

chlorine dioxide and monochloramine were ineffective oxidants and required longer contact times and

larger dosages as the ones established using the stoichiometric value in order to achieve considerable

oxidation efficiencies.

51

In the following Table 4.32, the estimated costs for the oxidation process using either ozone, chlorine or

potassium permanganate, are shown. It should be noted that the feed system used for potassium

permanganate is similar to the one considered for the coagulation unit process.

Table 4.32 – Estimated costs of different alternatives for the oxidation process as a function of treatment capacity

Oxidation alternative


15 50 100 200 300 450

Ozonization



Total O&M costs (k€) 2.8 2.9 3.0 3.2 3.6 4.0

Total AAC (k€) 5.6 6.0 6.6 6.6 7.9 9.7

Cost per m3 (€) 1.020 0.329 0.181 0.090 0.072 0.059

Potassium permanganate



Total O&M costs (k€) 3.5 4.0 4.7 6.1 7.6 9.8

Total AAC (k€) 6.1 6.6 7.4 8.9 10.4 13.0

Cost per m3 (€) 1.118 0.362 0.204 0.121 0.095 0.079

Chlorine dioxide



Total O&M costs (k€) 4.6 5.4 6.3 8.1 10.0 12.8

Total AAC (k€) 10.0 10.8 11.8 13.7 15.8 19.1

Cost per m3 (€) 1.830 0.594 0.324 0.188 0.144 0.116

52

5 Water treatment residuals management cost

analysis

5.1 Process residuals generated

Some of the processes presented in the previous subchapter produce residuals that must be taken into

account when designing a treatment system. The choice of a certain residual treatment alternative

depends fundamentally on the type, quantity, toxicity and generation frequency of the residuals. Table

5.1 shows, according to each treatment process, the type of residuals generated and their generation

frequencies.

Table 5.1 –Treatment technologies and residuals generated

Technology Residuals generated Type of residual Generation frequency

Sand or DE filtration Spent backwash Liquid Intermittent

Spent media Solid Intermittent

GAC and AA

Spent regenerant Liquid Intermittent

Spent backwash Liquid Intermittent

Spent media Solid Intermittent

Ion exchange

Spent brine Liquid Intermittent/Continuous

Spent backwash Liquid Intermittent

Spent resin Solid Intermittent

Membrane filtration

Spent backwash/tank drain and cross flow Liquid Intermittent

Cleaning waste Liquid Intermittent

Spent membrane modules Solid Intermittent

RO and NF

Membrane concentrate Liquid Continuous

Cleaning waste Liquid Intermittent

Spent membrane elements Solid Intermittent

Used cartridge filters Solid Intermittent

UV Spent lamps, ballasts and intensity sensors Solid Intermittent

Adapted from Exhibit C-1 in WBS-Based Cost Models from Drinking Water Treatment Technologies. (EPA, 2014)

As it can be observed in Table 5.1, there are two different types of residuals, liquid and solid. While the

solid residuals can be divided into toxic and non-toxic, the liquid residuals might be broken down into

the following five: backwash, softening, coagulation, brine and RO/NF membrane concentrate residuals.

53

Regarding both types of residuals, it is opportune to refer some general assumptions before proceeding

into the cost estimation of the residual management processes. As it was already done in the cost

analysis of some of the previous treatment processes, namely in coagulation, due to the high number

of variables, it is better to calculate the costs between two extreme situations in order to get a general

range of values instead of the costs for a specific solution. Therefore, in one situation, relatively high

conservative amounts of generated residuals were assumed and on the other one, the exact opposite.

The first of the liquid residuals, the backwash residuals, depend mainly on the total suspended soils

(TSS) that are in the water. In order to establish a conservative value for the backwash residuals

generated, the first step was to relate the TSS with the turbidity parameter NTU. It was shown that TSS

and NTU are fairly well correlated and that the ratio of TSS to NTU is about 4:5

with a R2 value of 0.8 (Daphne, et al., 2011). Therefore, by assuming either a high influent NTU value

of 10, or low NTU of 1, and a effluent target value of 0,1 NTU, the amount of TSS generated will be 0.72

mg/l in the least demanding situation, and 7.92 mg/l in the most demanding. In addition, it was also

defined that there was an average 5 m3 volume of backwash liquid generated daily for a 450 m3

treatment capacity and a 0.5 m3 volume for a 15 m3 treatment capacity and that these backwash liquid

volumes followed a linear equation between both treatment capacities.

As for the softening residuals, it is known that per 1 g of softening lime added, 0.4 g of residuals are

generated (EPA, 1977). Therefore, if we take into consideration the range of values established in the

water stabilization subchapter, the value for the softening residuals generated will be between 2 and

10 g/l.

In the case of the coagulation residuals, the residuals generated depend on the type of coagulant

applied. It is known that ferric chloride generates more residuals than aluminum sulfate and that 40% of

the amount of coagulant added in the case of ferric chloride turns into residuals (EPA, 1977).

Therefore, according to the values established for the coagulation process, residual concentrations

between 0 and 8.8 mg/l are expected.

Brine backwash residuals, generated from ion exchange, have highly variable characteristics and are

difficult to quantify. Nonetheless, based on backwash samples of a zeolite plant (EPA, 1977), a value of

about 15 mg/L was assumed. Additionally, based on the design of the ion exchange process, it was

assumed that the highest backwash rate was about 1000 backwashes per year with a volume per

backwash of 1 m3 and the lowest rate was 250 backwashes per year with a volume of 0.15 m3.

In regard to RO and NF membrane concentrate residuals, since it was previously assumed that any of

these processes had a permeate flow of 80%, these represent 20% of the influent flow. As a result, the

volume of concentrate residuals generated per day is between 3.75 and 112.5 m3.

Finally, in the case of solid residuals, it was assumed that the solids generated from any water treatment

process but activated alumina were non-hazardous and they would be disposed via an off-site disposal.

In the case of activated alumina, it was assumed that the resultant waste was also disposed via an

off-site solution but they were regarded as being hazardous.

54

5.2 Process residual disposal methods

Based on the treatment technology processes, the different residual disposal alternatives that will be

analyzed are the following:

Off-site disposal;

Direct discharge to surface water;

Holding tanks;

Evaporation ponds;

Discharge to a publicly owned treatment works;

Septic systems;

Land application;

It is important to refer that there are other alternatives that were not considered. On-site disposal could

be an option if on-site landfills exist, but this alternative was not considered due to the fact that off-site

disposal can be used as a conservative cost estimate for on-site disposal due to its higher costs.

Furthermore, deep well injection has emerged in the recent years as another possible alternative, but

this type of system is more adequate for large scale systems (EPA, 2006). Last but not least, due to the

reduced quantities of gas that are produced in the aeration processes, an off-gas treatment is not

required.

5.2.1 Off-site disposal

The annual disposal cost of residuals using an off-site disposal alternative follows the following

Equation 4:

𝐴𝑛𝑛𝑢𝑎𝑙 𝑑𝑖𝑠𝑝𝑜𝑠𝑎𝑙 𝑐𝑜𝑠𝑡𝑠 = 𝐷𝑖𝑠𝑝𝑜𝑠𝑎𝑙 𝑐𝑜𝑠𝑡𝑠 + 𝑇𝑟𝑎𝑛𝑠𝑝𝑜𝑟𝑡𝑎𝑡𝑖𝑜𝑛 (4)

where:

Disposal costs = quantity of solids per disposal event (in ton/l/event) x disposal frequency (in

events/yr) x unit cost for waste disposal (in €/ton/l) ;

Transportation costs = quantity of solids per disposal event (in tons/l/event) x disposal frequency

(in events/yr) x distance to disposal site (in km) x unit cost waste transportation (in €/ton/l/km).

The costs of an off-site disposal alternative are different according to the hazardousness of the waste

that must be disposed. The relevant assumptions regarding the waste disposal costs and travel

distances according to the hazardousness of the waste are the following:

15 km to the nearest non-hazardous waste disposal site;

300 km to the nearest hazardous waste disposal site;

55

Maximum waste shipment size of 18 tons or 22 m3;

Cost of non-hazardous waste disposal of 60.68 €/ton and a transportation cost of

0.28 €/(ton.km);

Cost of hazardous waste disposal of 308.91 €/ton, a minimum charge per shipment of 2649.5 €

and a transportation cost of 0.06 €/(ton.km).

5.2.2 Direct discharge to surface water

Some liquid residuals can be discharged directly into the surface water. In the USA, a National Pollutant

Discharge Elimination System permit is required to do so. The permit costs are displayed in the following

Table 5.2.

Table 5.2 – NPDES permit costs according to flow discharge

Average flow discharge (m3/day) Cost

0 2253.5 €

26.5 3380.2 €

265 5971.9 €

This alternative also requires additional equipment such as piping, valves and residual pumps that must

be included in capital and maintenance costs. The assumption was made that the discharge site is

located close to the water treatment plant and the total piping required is 15 m.

5.2.3 Discharge to a publicly owned treatment works

The discharge of residuals to a publicly owned treatment work (POTW) requires a certain minimum

quality of the residuals so that these residuals don’t overwhelm the capacity of the residual water

treatment plant downstream. Publicly owned treatment works often charge fees so that their services

can be used. These fees can be broken down into the following different types:

Flat fees (€/month);

Volume-based fees (€/m3 discharged);

Total dissolved solids-based fees (€/kg of TSS).

Taking into account these fees, it was assumed that the cost of residual discharge would follow the

following Equation 5:

𝐷𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 𝑐𝑜𝑠𝑡𝑠 = 𝐹𝑙𝑎𝑡 𝑓𝑒𝑒𝑠 + 𝑉𝑜𝑙𝑢𝑚𝑒 𝑓𝑒𝑒𝑠 (5)

Regarding the variables included in Equation 5, it was assumed that the flat fee for the POTW was

15.3 €/month and that the volume fee was 1.05 €/m3.

56

5.2.4 Evaporation ponds

Evaporations ponds are a viable alternative for managing liquid residuals produced by small water

treatment plants in arid climates (Jensen & Darby, 2016). The design of an evaporation ponds depends

strongly on evaporation and precipitation rates. In order to estimate the costs of a pond it is inevitable

to consider the following assumptions regarding these rates:

An annual precipitation of 700 mm, corresponding to an arid climate;

An annual evaporation of 1800 mm, measured in an evaporation tin;

A ratio of evaporation of 0.75 in order to take into account the value of evaporation that was

measured in a standard evaporation pan;

A safety factor of 1.1 for the value of the annual evaporation.

Additionally, some assumptions were made regarding the dimensions and the geometry of the

evaporations ponds:

Maximum size of 4 ha;

The slope of the pond has a declivity of 2/1 (H:V);

Freeboard of 0.3 m and an over-excavation of 0.5 m;

Length-width ratio of 2 and depth of 0.7 m.

The pond has enough capacity to hold the backwash volume produced during 180 days, which

corresponds to the number of the days within a year with no net evaporation.

Last but not least, some assumptions related with the maintenance of the evaporation ponds were made:

Substrate removal frequency of once per year;

The substrate was disposed off-site.

Substrate density of 2000 kg/m3.

In the following Table 5.3, displayed in the following page, the cost estimation of the evaporation pond

alternative for both residual generation situations previously defined is shown as a function of the daily

treatment capacity.

57

Table 5.3 – Estimated costs for an evaporation pond as a function of treatment capacity for

different values of residuals generated

Residuals generated by

process backwash

Parameter


15 50 100 200 300 450

Daily backwashed volume (m3)

0.5 1 2 3 4 5

7.9 mg/L TSS 25 mg/L softening 20 mg/L coag. 15 mg/L brine



Total O&M costs (k€) 0.5 0.9 1.7 2.6 3.6 4.6

Total AAC (k€) 2.1 4.1 7.5 11.2 15.3 19.6

Cost per m3 (€) 0.392 0.223 0.206 0.154 0.139 0.119

0.7 mg/L TSS 5 mg/L softening 15 mg/L brine

Total O&M costs (k€) 0.5 0.9 1.8 2.7 3.7 4.6

Total AAC (k€) 2.2 4.1 7.6 11.3 15.4 19.6

Cost per m3 (€) 0.394 0.224 0.208 0.155 0.141 0.119

Note: The useful life and capital costs are the same for both situations of residual generation.

5.2.5 Holding tanks

Holding tanks are used to equalize the rate of flow at which residuals are released or discharged. It is

very useful for managing intermittently generated liquid residuals that are ultimately discharged into a

publicly owned treatment work, the surface water or are reintroduced into the treatment plant. The use

of this type of tank also allows a gradual discharge of these residuals over time between generation

events so that the flow of residuals doesn’t overwhelm the residual treatment capacity of its final

destination.

The use of holding tanks also results in the generation of secondary residuals through the settling of the

suspended solids at the bottom of the tank. It was assumed that these residuals were moved to their

final destination manually by the operator. Additionally, it is known that the efficiency of the settling

process might be improved through the use of coagulants. Regarding this last aspect and the removal

of residuals from the tank, the following assumptions were made:

Due to its increased costs it was decided not to include coagulation in the holding tank;

A 25% of the total suspended solids present in the residuals are settled in a holding tank when

no coagulant is used;

Holding tank solid residuals have a density of 2000 kg/m3;

Holding tank solids are removed when their accumulation reaches 10% of the total tank

capacity.

58

Last but not least, it should be noted that, with the aim of reducing costs, the concrete tanks that were

set by default in the WBS models were replaced with cheaper plastic tanks. Without further ado, in the

following Table 5.4, the estimated costs of an holding tank solution is shown as a function of the daily

treatment capacity for different types of flow.

Table 5.4 – Estimated costs for a holding tank as a function of treatment capacity for

different types of flow

Type of flow Parameter Daily treatment capacity (m3)

15 50 100 200 300 450

Intermittent flow



Total O&M costs (k€) 1.8 1.9 2.2 2.6 3.0 3.7

Total AAC (k€) 3.0 3.2 3.5 3.9 4.5 5.4

Cost per m3 (€) 0.424 0.133 0.074 0.041 0.031 0.026

Continuous flow



Total O&M costs (k€) 3.0 3.1 3.3 3.7 4.2 4.8

Total AAC (k€) 7.6 7.8 8.1 8.5 9.1 10.1

Cost per m3 (€) 1.074 0.328 0.171 0.090 0.064 0.047

5.2.6 Septic systems

The use of a septic system can be an alternative for small treatment plants using technologies with

intermittent liquid generation. A septic system is composed by a septic tank(s) and an infiltration system.

It is an interesting option to consider when direct discharges are not possible and the off-site disposal

transportation costs are high. Regarding the design of the septic systems, the following assumptions

were made:

A minimum septic tank discharge time of 2 days;

The septic tanks used were prefabricated in fiberglass;

Septic tank volume safety factor of 1.5;

An infiltration rate of 20 l per m2 of soil;

Septic drain field trench with a width and depth of 1 m;

Septic drain field trench gravel depth below the distribution pipe of 0.3 m;

A minimum of two septic drain field trenches with 2.5 m between them;

A maximum septic drain field trench length of 30 m;

59

Septic drain field trench total gravel depth of 0.7 m with the pipe located in the middle of the

layer;

Septic drain field buffer distance of 3 m;

Septic tank over-excavation depth of 0.5 m ;

A maximum of 7 distribution pipes connections per distribution box;

Additionally, the same assumptions that were made for the maintenance of evaporation ponds were

made for the maintenance of septic tanks. The cost estimation for the septic tank alternative for both

residual generation situations previously defined is shown in the following Table 5.5 as a function of the

daily treatment capacity.

Table 5.5 – Estimated costs for a septic tank as a function of treatment capacity for different

values of residuals generated

Residuals generated by

process backwash

Parameter


15 50 100 200 300 450

Daily backwashed volume (m3)

0.5 1 2 3 4 5

7.9 mg/L TSS 25 mg/L softening 20 mg/L coagul. 15 mg/L brine

Useful life (years) 20 20 20 20 20 20


Total O&M costs (k€) 0.5 0.5 0.9 1.3 1.7 2.8

Total AAC (k€) 1.5 1.9 3.6 5.1 7.0 11.6

Cost per m3 (€) 0.281 0.103 0.098 0.070 0.064 0.071

0.7 mg/L TSS 5 mg/L softening 15 mg/L brine

Total O&M costs (k€) 0.6 0.6 1.0 1.4 1.8 2.9

Total AAC (k€) 1.6 2.0 3.7 5.2 7.1 11.7

Cost per m3 (€) 0.296 0.108 0.100 0.071 0.065 0.071

Note: The useful life and capital costs are the same for both situations of residual generation.

60

6 Treatment schemes definition and cost analysis

6.1 Treatment schemes definition

The purpose of this subchapter is to establish a treatment scheme matrix according to the removal

efficiency requirements by using the expected efficiencies and estimated costs of the unit processes

that were defined and calculated throughout chapter 4. First, in order to achieve this, it is important to

summarize the removal efficiency requirements already established back in chapter 2. The following

Table 6.1 shows the average removal efficiencies required for each class and each group of parameters

included in Table 2.3.

Table 6.1 – Average removal efficiencies required

Pollutant group A1 A2 A3

Pathogenic microorganisms log 3 log 5 log 6

Heavy metals and inorganic substances 61% 82% 93%

Volatile and non-volatile synthetic organic compounds 62% 82% 94%

The treatment scheme matrix is defined by intersecting three different matrixes, each one of them

corresponding to each one of the group of pollutants in Table 6.1.

The first matrix, the one regarding pathogenic microorganisms, is shown in Table 6.2, displayed in the

following page. The first row of the pathogenic microorganism treatment scheme matrix requires a

efficiency of 3-log. Through the comparison of the different filtration methods shown in subchapter 4.6,

it is possible to observe that the cheapest method is bag filtration, which has an expected filtration

efficiency of about 1 to 2-log for E.coli. In order to reach the required 3-log efficiency, a disinfection

process was also included. Since it is expected for disinfection processes to have a efficiency of about

3-log, it was assumed that the combination of both filtration and disinfection would produce a

conservative efficiency for this row. As such, the solution chosen for the first row of this matrix is a

treatment consisting of a bag filtration together with the second cheapest disinfection alternative, which

is gaseous chlorine. Gaseous chlorine was chosen over ozone, which is the cheapest disinfection

alternative, due to the fact that ozone doesn’t leave a residual disinfectant.

The A2 row requires a removal efficiency of 5-log. In order to achieve this efficiency, three treatment

processes were chosen. Contrary to the first row, because of its slightly higher pathogenic removal

efficiency and low relative cost when compared to other filtration methods, the choice fell on rapid sand

filtration. On top of this, in order to increase the overall efficiency of the rapid sand filtration system, a

coagulation process was also incorporated. Based on what was mentioned in subchapter relative to

coagulation, it is expected that the coagulation process increases the expected 1 to 3-log rapid sand

61

efficiency by another 1 or 2-log. Then, by adding a gaseous chlorine disinfection process, it was

assumed that the disinfection efficiency could eventually reach the 5 log requirement.

As for the A3 row, in order to establish a scheme to reach an efficiency of 6 log, two different possible

alternatives were taken into account. The treatment could be done by either giving more emphasis on

the filtration or on the disinfection component. If a higher emphasis would be given to filtration, a

membrane process such as NF or RO should be included due to their removal efficiencies above 4-log.

On the contrary, if a higher emphasis was to be given to disinfection, a high standard disinfection

process, such as UV disinfection, should be incorporated. The choice between both alternatives fell on

UV. UV is cheaper when directly compared with both NF and RO. On the other hand, it is known that

both NF and RO processes require a pre-filtration process such as ultrafiltration. It could be argued that

UV also requires another extra disinfection process in order to leave a residual disinfectant in the water,

but, even in that case, the overall cost of UV together with a cheap disinfection alternative, such as

gaseous chlorine, would be much lower than the one of NF/RO along with a pre-filtration process.

Therefore, the treatment solution chosen consists of a rapid sand filtration stage, supported by

coagulation, together with a disinfection stage consisting of a UV disinfection reactor and a gaseous

chlorine feeding system. The matrix concerning the treatment solutions for the removal of pathogenic

microorganisms is shown in the following Table 6.2.

Table 6.2 – Treatment solutions for pathogenic microorganisms


A1 A2 A3

Path

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A1

Bag filtration + Gaseous chlorine

A1

Sy

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A2

A3

A2

Coagulation + Rapid sand filtration + Gaseous chlorine

A1

A2

A3

A3

Coagulation + Rapid sand filtration + UV disinfection + Gaseous chlorine

A1

A2

A3

62

Proceeding further ahead, the matrix concerning the treatment processes required for the treatment of

heavy metals and inorganic substances is shown in Table 6.3, which is displayed in the following page.

According to the previous Table 6.1 the efficiency required for these substances ranges from about 60

to 90%.

The treatment processes that aim at removing heavy metals and inorganics include processes such as

AA adsorption, RO, ion exchange, oxidation, and rapid sand filtration with coagulation. Among these

processes, rapid sand filtration has the lowest removal efficiency value of about 60%, and the remaining

processes have removal efficiencies above 80-90% for most substances.

The choice among alternatives must not focus merely on the removal efficiency and costs. Other

aspects, such as the application scope of each process in the removal of inorganic substances and the

removal efficiencies of the other groups of contaminants, must also be taken into account.

The scope of application of each alternative was analyzed in (Mahmood, et al., 2007). RO, although

being more expensive than the other alternatives, can virtually remove any type of heavy metal or

inorganic substance. As for ion exchange, as it was previously mentioned, due to the fact that fluoride

has less affinity towards an anionic resion than other anions have, ion exchange is often incapable of

removing it. On the other hand, because ion exchange only has 30% removal efficiency for As(III) and

90% for As(V), a supplementary pre-oxidation stage is often required. Furthermore, when compared

with AA adsorption, ion exchange has the advantage of being capable of removing nitrates with

efficiencies higher than AA. AA adsorption, however, besides being capable of removing As(III) with

efficiencies of about 60%, it is also capable of removing fluorides with efficiencies of about 90%.

As for the relationship between the treatment processes of inorganic substances and the other groups

of contaminants, rapid sand has an advantage over the other processes. Rapid sand filtration, as it was

mentioned before, has the ability of removing pathogenic microorganisms and it was, in fact, included

in the treatment solutions shown in Table 6.2. Therefore, by choosing rapid sand filtration for the

treatment of inorganic substances, a single process handles two different groups of contaminants and

reduces overall costs by doing so. Regarding the other treatment alternatives besides RO, which can

remove any pollutant, it is known that ozone oxidation has an impact on the pathogenic microorganisms

and VOCs, and, as such, its inclusion would also improve the overall treatment effectiveness. AA

adsorption and ion exchange are only design to remove heavy metals and inorganic substances and

hardly have any influence on other contaminants.

Taking into account everything that was aforementioned, a rapid sand treatment supported by

coagulation was chosen for the A1 column. Also, if the water has a high enough fluoride concentration,

an AA adsorption process must be included. The same applies for ion exchange regarding nitrates. As

for the A2 and A3 columns, AA adsorption accompanied by ozone oxidation is the best choice if there

are no nitrates and the water contains fluorides. If the water eventually has nitrates and no fluorides, ion

exchange together with ozone oxidation was considered as being the best option. On the other hand, if

the water has both fluorides and nitrates, AA adsorption, ion exchange and ozone oxidation must be

included. The treatment solutions are compiled in following Table 6.3, displayed in the following page.

63

Table 6.3 - Treatment solutions for heavy metals and inorganic substances


A1 A2 A3

Path

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A1

Coagulation + rapid

sand filtration + AA

adsorption if fluoride

exists + Ion exchange

if nitrate exists.

AA adsorption + ozone

oxidation if there are

no nitrates and ion

exchange + ozone

oxidation otherwise.

Include both AA

adsorption and ion

exchange + ozone

oxidation if water has

both fluoride and

nitrates.

AA adsorption + ozone

oxidation if there are

no nitrates and ion

exchange + ozone

oxidation otherwise.

Include both AA

adsorption and ion

exchange + ozone

oxidation if water has

both fluoride and

nitrates.

A1

Sy

nth

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org

an

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om

po

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A2

A3

A2

A1

A2

A3

A3

A1

A2

A3

The last matrix that was defined was the matrix concerning volatile and non-volatile synthetic organic

compounds. Both aeration methods that were analyzed back in subchapter 4.1, PTA and MSBA, are

capable or removing VOCs with any efficiency required, but should not be used in the presence of non-

volatile organic compounds. In such case, GAC adsorption is more appropriate. This alternative is

capable of removing either volatile and non-volatile compounds.

By comparing the costs of each alternative, it is possible to affirm that GAC should be chosen in order

to treat VOCs and, as such, taking into consideration the aforesaid, the treatment chosen for the every

row was GAC. The matrix of synthetic organic compounds treatment alternatives is shown in the

following Table 6.4Table 6.4Error! Reference source not found., displayed in the following page.

64

Table 6.4 – Treatment solutions for volatile and non-volatile synthetic organic substances


A1 A2 A3

Path

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A1

GAC

A1

Sy

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GAC

A2

GAC

A3

A2

GAC

A1

GAC

A2

GAC

A3

A

3

GAC

A1

GAC

A2

GAC

A3

Before intersecting the three matrixes defined, it is important to refer another fundamental point. It is

known that, although any of the unit processes included in any of the matrixes is individually cheaper

than RO, RO might be more economic when a considerable number of different water treatment unit

processes are arranged together into a treatment scheme. Therefore, a treatment alternative using RO

membrane filtration must be established in order to be compared with the treatment schemes that result

from the intersection of the matrixes.

It is known that, in the process of RO membrane filtration the influent water requires some kind of

pretreatment to avoid quick clogging and to assure residual disinfection treatment. Therefore, it was

assumed that the RO treatment alternative included also the following treatment processes:

Coagulation;

Rapid sand filtration;

Ultrafiltration

Gaseous chlorine.

Being the second treatment alternative defined, the matrixes were intersected in order to produce the

matrix that contains the treatment schemes whose costs were analyzed. This matrix is included in Table

6.6. As it was firstly intended, the different cells were classified taking into the account the distinction

that was earlier established between surface and groundwater. The blue cells represent a water whose

quality most closely resembles a surface water and the brown cells represent a water with a quality that

65

is expected from a groundwater. Grey color cells, on the other hand, according to what was established,

represent a water without a specific origin.

6.2 Cost analysis assumptions

The procedure of calculating the costs of each treatment scheme and type of water, due to the number

of variables, is quite complex. In order to simplify the procedure, some assumptions had to be made.

In spite of the innumerous different VOCs that might be present in the water, benzene was chosen as a

general representative of the group due to its median absorbance value and range of expected

concentrations. The benzene concentrations considered in the cost estimations followed the

concentrations established according to each class.

Regarding the group of pathogenic microorganisms, it was assumed that a chlorine dosage of 0.5 mg/l

was to be added regardless of the class of treatment required. It was decided to assume this rather

conservative value in order to reduce the dependency that the disinfection efficiency has on the

existence of reservoirs downstream of the treatment system or on the length of the distribution system.

As for the ferric chloride dosage in coagulation and the ozone dosage in oxidation, rather conservative

values were also assumed. As it was previously refered in subchapter 4.3, a ferric chloride dosage of

20 mg/L is conservative and is enough to achieve high coagulations efficiencies. The ozone dosage of

1.3 mg/L is also deemed as conservative due to the fact that it was calculated based on relatively high

concentrations of iron and manganese.

In respect to turbidity, values for the influent and effluent turbidity had to be assumed. The turbidity of

the water is generally somewhere in between 1 and 10 NTU. Based on this range of values, the

assumption was made that the influent water wouldn’t have neither a low nor high turbidity value, but

rather a value of 5 NTU, which reflects a more intermediate situation. As for the effluent turbidity, based

on the turbidity removal efficiencies of the filtration methods included in chapter 4, it was assumed that

regardless of the process chosen, an effluent turbidity of at least 0.1 mg/l would be achieved.

Lastly, similarly to benzene, in spite of the different inorganic compounds that might be present in the

water, only a couple of compounds were considered in the cost analysis. These were the arsenic and

nitrates. The arsenic and nitrate concentrations considered in the cost analysis were the same as the

ones defined for each contamination class.

The assumptions were compiled in the following Table 6.5, displayed in the following page. Other

assumptions, concerning the design of the unit treatment processes or the residual management

alternatives are the same as those assumed in their respective chapters.

66

Table 6.5 – General cost analysis assumptions

Parameter Value assumed

Chlorine dosage 0.5 mg/L

Ferric chloride dosage 20 mg/L

Ozone dosage in oxidation 1.3 mg/L

Influent turbidity 5 NTU

Effluent turbidity 0.1 NTU

Benzene concentration According to each class value

Arsenic concentration According to each class value

Nitrate concentration According to each class value

67

Table 6.6 - Water treatment scheme matrix

Surface water Groundwater Water without a specific origin


A1 A2 A3

Pa

tho

ge

nic

mic

roo

rga

nis

ms

A1

Alternative 1: Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

Alternative 1: Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon + Oxidation Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

Alternative 1: Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon + Oxidation Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

A1

Vo

latile

an

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A2

A3

A2

Alternative 1: Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

Alternative 1:Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon + Oxidation Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

Alternative 1:Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon + Oxidation Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

A1

A2

A3

A3

Alternative 1: Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon + UV disinfection Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

Alternative 1: Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon + Oxidation + UV disinfection Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

Alternative 1: Coagulation + Rapid sand filtration + Gaseous chlorine + Ion exchange + Activated alumina + Granular activated carbon + Oxidation + UV disinfection Alternative 2: Coagulation + Rapid sand filtration + Gaseous chlorine + Ultrafiltration + Reverse osmosis

A1

A2

A

3

68

7 Results and discussion

Results. The results consist of the unit costs of both alternative 1 and 2 and their respective unit residual

treatment costs. The unit costs calculated for the treatment alternative 1 are shown in Table 7.1 as a

function of the raw water quality and daily treatment capacity required. In order to have a better

understanding of the proportions of each unit process in the total unit costs of treatment alternative 1,

the costs of three different cells, the A(1,1,1), A(2,2,2), A(3,3,3) cells, which are outlined in Table 7.1

were broken down and compiled in Table 7.2. The unit costs of the residual treatments of treatment

alternative 1 were compiled in Table 7.3. As for the treatment alternative 2, both unit treatment costs

and unit residual treatment costs were compiled in one single table, Table 7.4.

Cost comparison of both treatment alternatives. The most economical alternative depends on

whether the raw water is contaminated with VOC’s, nitrates, fluorides or other heavy metals. If these

pollutants are absent, there are unit processes in alternative 1 that may be disregarded and the overall

cost of this alternative may be reduced. In the best case scenario, if the unit processes that are used to

treat VOC’s, nitrates and fluorides aren’t included in the treatment scheme, alternative 1 is overall

cheaper than alternative 2 regardless of the residual treatment process chosen. As for the worst case

scenario, if the treatment of the raw water requires a complete treatment scheme, the choice of the most

economical alternative depends mainly on the daily treatment required. For daily treatment capacities

below 50 m3/day, alternative 2 is the most economical alternative regardless of the residual treatment

chosen. For higher daily treatment capacities, however, alternative 1 starts becoming gradually more

economically viable. It can be noticed that, the higher the unit cost of the residual treatment is, the lower

the daily treatment capacity has to be for the alternative 1 to become more viable. In other words, if the

residual treatment consists of evaporation ponds and septic tanks, alternative 1 starts becoming more

viable than alternative 2 in the 50-200 m3/day range. On the other hand, if the residual treatment consists

of more economical methods such as POTW, alongside with holding tanks, alternative 1 becomes more

viable only after the 300-400 m3/day range. Lastly, it should be noted that the unit costs of the surface

discharge residual management alternative is always lower for alternative 2 and, as such, for the worst

case cenario, the combination of alternative 2 with surface discharge is the most economical method

possible regardless of the daily treatment capacity.

Surface water unit cost vs. groundwater unit cost. Surface water unit costs are slightly lower than

groundwater costs. This outcome is different from the results reached by other authors. These have

shown that treatment systems that use surface water are found to be more expensive to build and

operate than groundwater systems (Janzen, et al., 2016). The reason behind this difference in costs lies

in the fact that the costs analysis was done considering a complete and extensive treatment scheme

that included processes such as IX, AA and GAC. These three processes, by themselves, make more

than 50% of the water treatment costs. Therefore, if a more tailored solution is used to address a specific

groundwater contamination problem, the groundwater unit costs will be substantially lower than the

69

surface water unit costs. Last but not least, it should also be noted that, despite not being as relevant

as the last point mentioned, the unit costs in the article also include some appurtenances in the total

capital costs that were not included in the costs analysis done, such as water catchment structures and

reservoirs.

The absolute value of the treatment unit cost. Through the comparison of the median absolute values

of alternative 1, calculated from the unit cost values found in Table 7.1 for the different treatment

capacities of both surface and groundwater, with the surface and groundwater cost equations in

(Janzen, et al., 2016), it is possible to notice that the median absolute surface water unit cost values

calculated are, on average, 62% lower, and in the case of groundwater, 22% lower.

Process costs from EPA provided WBS models vs. established models using the same

framework. It seems that the costs calculated through the direct use of the GAC, PTA and MSBA

models provided by EPA are substantially higher than the costs calculated for the remaining unit

treatment process by following the same framework. It was noticed that the cost difference is mainly due

to the higher treatment process costs (i.e. costs with pressure vessels, chemical generators, pipes,

valves) that were obtained by using the item cost equations established by EPA in its provided models.

In these process costs, since the pipe and valve unit costs were the same throughout the models, the

only remarkable difference between the models established using the WBS framework and those

already provided by EPA was the main process appurtenance (i.e. pressure vessels, chemical

generators, membranes, etc.). Even by assuming an equipment transportation-installation coefficient

substantially higher than the ones assumed by EPA in its cost calculations (2 vs. a median value of 1.37

with a maximum value of about 1.8), the GAC pressure vessel cost, for instance, was much higher than

the main appurtenance required for technologies such as UV disinfection (UV reactors) or membrane

filtration. Therefore, either the unit treatment process models established are under designed in terms

of process equipment or some of the cost equations calculated by EPA are overestimated.

Synthetic organic pollutant treatment unit process costs. By comparing the first three unit

processes analyzed (PTA, MSBA and GAC adsorption), which are used to remove synthetic organic

compounds, it seems that both PTA and MSBA are cheaper than GAC and are a better choice in

removing synthetic volatile compounds. The reason behind this are the operational costs of GAC, which

are reasonably higher by virtue of the frequent media replacement. The unit costs of both PTA and GAC

were also compared with cost values found throughout the literature. The unit costs calculated for the

PTA are lower than the actualized costs of two aerators, one of 0.1 mgd and the other one of 0.029 mgd,

both found in (Logsdon, et al., 1990). While the cost values calculated for a 0.1 mgd ranged from 0.078

to 0.181 €/m3, the aerator found had a cost of 0.195 €/m3. As for the second aerator, the values

calculated ranged from 0.251 to 0.435 €/m3 and the cost of the aerator was 0.480 €/m3. In the case of

GAC, the range of values calculated was compared with a 0.1 mgd GAC process found in the same

study. While the annualized unit cost value found was 0.832 €/m3, the value calculated through the WBS

model ranged from 0.125 to 0.504 €/m3. In comparison to their unit price during the 90’s, while the price

of PTA has decreased from 9 to 40%, the GAC unit price has decreased from 40 to 85%.

70

Filtration unit process costs. Among the different filtration processes analyzed, due to their

operational simplicity, bag and rapid sand filtration are the cheapest alternatives for higher treatment

capacities. On the low end of the daily treatment range, among all the alternatives, slow sand filtration

is the cheapest one. As for DE filtration, it seems that this filtration is not suitable for small water

treatment plants due to the high O&M costs that arise from the constant need of replacing the filtration

media by virtue of the process’s working intermittence. As for membrane filtration and membrane

processes, these are the most expensive alternatives even without taking into account their required

pre-treatment processes. The costs of the filtration processes were also compared with some unit costs

found throughout the literature. In the case of DE filtration,it was found in (Logsdon, et al., 1990) that its

actualized unit cost is 0.546 €/m3 for a 0.1 mgd treatment capacity, which is 116-359% higher than the

range of values calculated for the same capacity, which ranged from 0.152 to 0.471 €/m3. As for slow

sand filtration, the value in the same study for the same treatment capacity was 1.105 €/m3, 343% lower

than the unit cost value calculated of 0.322 €/m3. Last but not least, comparing the results obtained for

RO unit process with the results found in the same study, it is possible to notice that, after adjusting the

costs for inflation, the value calculated for the RO unit process is 79% lower than it was 26 years ago

for a treatment capacity of 0.01 mgd (37.8 m3/day), and 92% lower for a treatment capacity of 0.1 mgd

(378 m3/day).

Disinfection unit process costs. Through the comparison of the different chlorination methods, it

seems that the most economical alternative is gaseous chlorine, followed by the calcium hypochlorite

tablet and the sodium hypochlorite solution alternatives. This is explained by the fact that, while the

other two alternatives use chlorine products with purities below 100%, gaseous chlorine uses chlorine

in its purest form. The cost difference between the different chlorine products doesn’t compensate the

difference between their chlorine contents. As for other disinfection processes, it is interesting to observe

that ozone disinfection was the most economical alternative among all the processes analyzed, being

even ahead of chlorination and UV disinfection. These results are different from what was initially

expected. In fact, according to (EPA, 1996) and (Wolfe, 1990), ozone was the less economical

disinfection alternative when compared with UV disinfection and chlorination. It is suspected that the

reason behind this result lies in the ozone generator assumed for the cost analysis. It is known that

many ozone generators use pure oxygen tanks in order to produce ozone, and in the cost analysis the

ozone generators used dried atmospheric air instead. The least economical disinfection alternatives

were the chloramination and the disinfection through dioxide chlorine. In the case of dioxide chlorine,

besides requiring an input of Nadolyt, its generator is quite expensive. As for chloramination, its higher

costs are explained by its higher reagent requirements. The disinfection unit process costs were also

compared with values found in other studies. While in (EPA, 1996) the actualized chlorination unit costs,

using a 5 mg/L dosage, for daily treatment capacities of 21.2, 90.7 and 325.1 m3 were 0.415, 0.104 and

0.03 €/m3 respectively, the average calculated unit costs for the same capacities were 1.160, 0.289 and

0.111 €/m3. As for UV disinfection, while the unit costs found in the same study and for the same

capacities were 0.251, 0.059 and 0.029 €/m3, the UV calculated costs were 1.207, 0.257 and 0.091 €/m3.

The calculated ozonization unit costs, while considering using a 1 mg/L dosage, were significantly lower

than the ones found in (EPA, 1996), the calculated costs were 1.036, 0.218 and 0.077 €/m3 and the

71

report’s costs were 0.518, 0.148 and 0.044 €/m3. Last but not least, while the unit cost found in (Wolfe,

1990) for a chlorine dioxide alternative with a 0.05 mgd (189 m3) treatment capacity and using a dosage

of 2 mg/L was 0.906 €/m3, the cost calculated through the models was 0.209 €/m3.

Other unit process costs. The unit costs of AA adsorption and ion exchange were also compared with

unit values found throughout the scientific literature. The calculated value for AA adsorption unit cost for

the removal of arsenate and for a daily treatment capacity of 378 m3 was 0.044 €/m3, which is much

lower than the value of 0.637 €/m3 found in (Logsdon, et al., 1990). This difference might be due to the

fact that the value calculated for the unit cost didn’t include the additional costs of the residual

management. Regarding the unit cost of ion exchange, the same study has determined that both cationic

and anionic exchange have a similar cost of about 0.633 m3 for a treatment capacity of 378 m3. This

value is substantially higher than the ranges of costs that were calculated for both cationic and ionic

exchange, in the case of cationic exchange the range calculated was 0.138 to 0.193 €/m3 and in the

case of anionic exchange it was 0.067 to 0.197 €/m3.

Limitations of the classification system established. A classification system is the foundation for a

cost analysis that takes into account the quality of different kinds of water. Since the costs calculated

depend directly on the classification system adopted, the unit costs obtained should be analyzed while

taking into account that they were based on the Portuguese legal framework and my own personal

judgment together with expected occurrence values for some pollutants. On the other hand, the

distinction established between surface and groundwater is, in reality, not as linear as the one

established for the classification system. This distinction was merely established taking into account the

most probable contaminants in both types of water and nothing stops, for instance, a surface water from

being highly contaminated with inorganic substances and, at the same time, having no pathogenic

contamination.

Other limitations. While establishing the unit process models, many of the costs related to the

equipment required for the operation were obtained from contacting a small, non-statistically significant

number of different manufacturers. Therefore, the costs might vary somewhat by using equipment from

other manufacturers and the end results regarding the most economical alternative might be different.

Furthermore, other information, such as prices found throughout the literature to which the calculated

prices were compared, is also not statistically significant. On the other hand, the water treatment unit

costs were calculated exclusively from a theoretical point of view and they lack practical validation.

72

Table 7.1 – Highest values for the estimated costs in €/m3 for the alternative 1 treatment scheme

Surface water Groundwater Water without a specific origin Note: Please refer to Table 6.6 for the description of alternative 1.

Cell A(i,j,k)

i – pathogens

j – inorganics

k - organics


A1 A2 A3


15 50 100 200 300 450 15 50 100 200 300 450 15 50 100 200 300 450

Path

og

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icro

org

an

ism

s

6.338 2.096 1.299 0.804 0.641 0.581 6.546 2.209 1.389 0.864 0.704 0.660 6.600 2.264 1.444 0.919 0.758 0.732

A1

Vo

latile

an

d n

on

-vo

latile

syn

the

tic o

rgan

ic c

om

po

un

ds

A1

6.417 2.170 1.371 0.873 0.709 0.647 6.625 2.284 1.461 0.933 0.771 0.726 6.680 2.339 1.516 0.988 0.826 0.797

A2

7.005 2.721 1.902 1.384 1.209 1.138 7.213 2.835 1.992 1.444 1.271 1.217 7.268 2.890 2.047 1.499 1.326 1.289

A3

A2

6.338 2.096 1.299 0.804 0.641 0.581 6.546 2.209 1.389 0.864 0.704 0.660 6.600 2.264 1.444 0.919 0.758 0.732

A1

6.417 2.170 1.371 0.873 0.709 0.647 6.625 2.284 1.461 0.933 0.771 0.726 6.680 2.339 1.516 0.988 0.826 0.797

A2

7.005 2.721 1.902 1.384 1.209 1.138 7.213 2.835 1.992 1.444 1.271 1.217 7.268 2.890 2.047 1.499 1.326 1.289

A3

A3

6.527 2.152 1.328 0.828 0.666 0.599 6.734 2.266 1.418 0.889 0.729 0.678 6.789 2.321 1.473 0.943 0.783 0.749

A1

6.606 2.226 1.400 0.897 0.733 0.665 6.814 2.340 1.490 0.958 0.796 0.744 6.869 2.395 1.545 1.012 0.851 0.816

A2

7.194 2.777 1.931 1.409 1.234 1.156 7.402 2.891 2.021 1.469 1.296 1.236 7.456 2.946 2.076 1.524 1.351 1.307

A3

73

Table 7.2 – Cost breakdown in €/m3 of the A(1,1,1), A(2,2,2), and A(3,3,3) cells of Table 7.1

A(1,1,1) Cell Daily treatment capacity (m3)

15 50 100 200 300 450

GAC 1.067 16.8% 0.410 19.5% 0.316 24.3% 0.220 27.4% 0.181 28.2% 0.158 27.1%

AA 1.474 23.3% 0.483 23.1% 0.320 24.6% 0.190 23.6% 0.148 23.0% 0.118 20.3%

Coagulation 0.274 4.3% 0.114 5.4% 0.080 6.1% 0.062 7.8% 0.057 8.9% 0.053 9.1%

Gas chlorine 0.267 4.2% 0.081 3.9% 0.042 3.2% 0.022 2.7% 0.015 2.4% 0.011 1.9%

RSF 0.858 13.5% 0.261 12.5% 0.147 11.3% 0.082 10.2% 0.065 10.2% 0.070 12.0%

IX 1.337 21.1% 0.421 20.1% 0.223 17.2% 0.137 17.1% 0.109 17.0% 0.121 20.9%

Connection 1.062 16.8% 0.326 15.6% 0.171 13.1% 0.091 11.3% 0.066 10.3% 0.051 8.7%

Total 6.339 2.096 1.300 0.804 0.641 0.581


15 50 100 200 300 450

GAC 1.146 17.3% 0.484 21.2% 0.388 26.6% 0.289 30.9% 0.248 32.2% 0.224 30.8%

AA 1.497 22.6% 0.506 22.2% 0.343 23.5% 0.212 22.8% 0.170 22.1% 0.141 19.4%

Coagulation 0.274 4.1% 0.114 5.0% 0.080 5.5% 0.062 6.7% 0.057 7.4% 0.053 7.3%

Gas chlorine 0.267 4.0% 0.081 3.5% 0.042 2.9% 0.022 2.3% 0.015 2.0% 0.011 1.5%

RSF 0.858 12.9% 0.261 11.4% 0.147 10.0% 0.082 8.8% 0.065 8.5% 0.070 9.6%

Oz. Oxi 0.168 2.5% 0.074 3.2% 0.050 3.4% 0.020 2.2% 0.023 2.9% 0.021 2.9%

IX 1.355 20.4% 0.439 19.2% 0.241 16.5% 0.155 16.6% 0.126 16.4% 0.156 21.5%

Connection 1.062 16.0% 0.326 14.3% 0.171 11.7% 0.091 9.7% 0.066 8.5% 0.051 7.0%

Total 6.627 2.284 1.461 0.933 0.771 0.726


15 50 100 200 300 450

GAC 1.734 23.3% 1.035 35.1% 0.919 44.3% 0.800 52.5% 0.749 55.4% 0.715 54.7%

AA 1.535 20.6% 0.544 18.5% 0.381 18.4% 0.251 16.4% 0.209 15.4% 0.179 13.7%

Coagulation 0.274 3.7% 0.114 3.9% 0.080 3.8% 0.062 4.1% 0.057 4.2% 0.053 4.0%

Gas chlorine 0.267 3.6% 0.081 2.8% 0.042 2.0% 0.022 1.4% 0.015 1.1% 0.011 0.8%

RSF 0.858 11.5% 0.261 8.9% 0.147 7.1% 0.082 5.4% 0.065 4.8% 0.070 5.4%

Oz. Oxi 0.168 2.3% 0.074 2.5% 0.050 2.4% 0.020 1.3% 0.023 1.7% 0.021 1.6%

IX 1.371 18.4% 0.455 15.5% 0.258 12.4% 0.172 11.3% 0.143 10.6% 0.190 14.5%

UV 0.187 2.5% 0.056 1.9% 0.029 1.4% 0.025 1.6% 0.025 1.8% 0.018 1.4%

Connection 1.062 14.2% 0.326 11.1% 0.171 8.2% 0.091 6.0% 0.066 4.9% 0.051 3.9%

Total 7.457 2.946 2.076 1.524 1.351 1.307

74

Table 7.3 – Cost breakdown in €/m3 of the residual treatment solutions according to processes included in the treatment alternative 1

Evaporation pond Daily treatment capacity (m3)

15 50 100 200 300 450

GAC 0.530 25.5% 0.292 29.4% 0.287 33.8% 0.230 34.3% 0.228 35.1% 0.211 29.7%

AA 0.530 25.5% 0.292 29.4% 0.287 33.8% 0.230 34.3% 0.228 35.1% 0.211 29.7%

RSF 0.732 35.2% 0.216 21.7% 0.161 19.0% 0.125 18.6% 0.119 18.4% 0.158 22.3%

IX 0.144 6.9% 0.142 14.3% 0.081 9.5% 0.066 9.9% 0.058 9.0% 0.116 16.4%

Connection 0.143 6.9% 0.052 5.2% 0.034 4.0% 0.020 3.0% 0.016 2.4% 0.014 1.9%

Total 2.081 0.995 0.849 0.672 0.650 0.711

Septic Tank Daily treatment capacity (m3)

15 50 100 200 300 450

GAC 0.262 22.1% 0.152 25.7% 0.184 37.9% 0.120 32.0% 0.112 31.7% 0.112 29.0%

AA 0.262 22.1% 0.152 25.7% 0.184 37.9% 0.120 32.0% 0.112 31.7% 0.112 29.0%

RSF 0.242 20.5% 0.123 20.8% 0.058 11.9% 0.088 23.4% 0.073 20.6% 0.077 19.9%

IX 0.046 3.9% 0.110 18.6% 0.028 5.8% 0.025 6.5% 0.021 6.0% 0.062 16.1%

Connection 0.370 31.3% 0.054 9.1% 0.031 6.5% 0.023 6.0% 0.036 10.1% 0.024 6.1%

Total 1.182 0.592 0.486 0.376 0.354 0.387

POTW Daily treatment capacity (m3)

15 50 100 200 300 450

GAC 0.085 24.8% 0.048 29.4% 0.048 34.2% 0.040 34.9% 0.039 35.7% 0.037 30.5%

AA 0.085 24.8% 0.048 29.4% 0.048 34.2% 0.040 34.9% 0.039 35.7% 0.037 30.5%

RSF 0.116 33.9% 0.035 21.1% 0.026 18.6% 0.021 18.2% 0.020 18.0% 0.026 21.9%

IX 0.023 6.7% 0.023 14.0% 0.013 9.3% 0.011 9.6% 0.010 8.8% 0.019 16.1%

Connection 0.034 9.9% 0.010 6.2% 0.005 3.7% 0.003 2.4% 0.002 1.8% 0.001 1.1%

Total 0.343 0.165 0.142 0.113 0.110 0.121

Surface discharge Daily treatment capacity (m3)

15 50 100 200 300 450

GAC 0.002 3.9% 0.002 10.8% 0.002 17.4% 0.002 25.3% 0.002 29.7% 0.002 41.5%

AA 0.002 4.6% 0.002 12.7% 0.002 20.5% 0.002 29.8% 0.002 35.0% 0.002 46.8%

Connection 0.036 91.6% 0.011 76.6% 0.005 62.0% 0.003 44.9% 0.002 35.2% 0.001 11.7%

Total 0.039 0.014 0.009 0.006 0.005 0.005

HT + POTW Daily treatment capacity (m3)

15 50 100 200 300 450

GAC 0.085 12.2% 0.048 17.5% 0.048 23.7% 0.039 26.2% 0.041 29.6% 0.038 25.8%

AA 0.085 12.2% 0.049 17.6% 0.049 23.8% 0.040 26.4% 0.041 29.8% 0.038 26.0%

Coagulation 0.005 0.7% 0.002 0.7% 0.001 0.6% 0.001 0.6% 0.001 0.5% 0.001 0.5%

RSF 0.116 16.7% 0.035 12.7% 0.027 13.0% 0.023 15.6% 0.020 14.5% 0.028 19.0%

IX 0.023 3.3% 0.023 8.4% 0.013 6.5% 0.011 7.3% 0.010 7.0% 0.021 14.1%

Connection 0.382 54.9% 0.119 43.0% 0.066 32.4% 0.036 23.9% 0.026 18.5% 0.022 14.7%

Total 0.697 0.276 0.204 0.150 0.138 0.146

HT + Surface discharge Daily treatment capacity (m3)

15 50 100 200 300 450

GAC 0.002 0.4% 0.002 1.2% 0.002 2.1% 0.004 9.5% 0.003 9.4% 0.003 10.5%

AA 0.002 0.5% 0.002 1.4% 0.002 2.5% 0.004 10.1% 0.004 10.2% 0.004 11.4%

Coagulation 0.005 1.2% 0.002 1.4% 0.001 1.6% 0.001 2.0% 0.001 2.1% 0.001 2.1%

RSF 0.000 0.1% 0.000 0.2% 0.000 0.4% 0.000 0.6% 0.001 3.4% 0.001 4.5%

IX 0.000 0.0% 0.000 0.0% 0.000 0.0% 0.000 0.0% 0.000 0.0% 0.001 3.7%

Connection 0.386 97.9% 0.120 95.7% 0.067 93.4% 0.034 77.9% 0.026 74.8% 0.021 67.7%

Total 0.394 0.0% 0.125 0.0% 0.071 0.0% 0.043 0.0% 0.034 0.0% 0.031 0.0%

75

Table 7.4 – Cost breakdown in euros of treatment alternative 2 and its residual treatment solutions.

Alternative 2 Daily treatment capacity (m3)

15 50 100 200 300 450

Coagulation 0.276 8.0% 0.122 10.8% 0.090 12.6% 0.072 13.9% 0.067 14.4% 0.059 12.7%

Gas chlorine 0.264 7.7% 0.080 7.1% 0.041 5.7% 0.021 4.1% 0.015 3.2% 0.010 2.2%

RSF 0.847 24.6% 0.162 14.3% 0.086 12.0% 0.049 9.5% 0.037 8.1% 0.083 17.9%

UF 0.708 20.6% 0.261 23.2% 0.241 33.5% 0.117 22.5% 0.109 23.5% 0.099 21.4%

RO 0.231 6.7% 0.134 11.9% 0.133 18.5% 0.129 24.8% 0.127 27.5% 0.126 27.2%

Connection 1.115 32.4% 0.368 32.7% 0.127 17.7% 0.131 25.2% 0.108 23.3% 0.087 18.7%

Total 3.441 1.127 0.718 0.520 0.463 0.464

Evaporation pond Daily treatment capacity (m3)

15 50 100 200 300 450

Coagulation 0.001 0.0% 0.001 0.0% 0.001 0.0% 0.001 34.3% 0.001 0.0% 0.001 29.7%

RSF 0.722 26.7% 0.212 10.3% 0.159 8.1% 0.246 34.3% 0.236 11.8% 0.157 29.7%

UF 0.178 6.6% 0.173 8.4% 0.171 8.7% 0.170 18.6% 0.170 8.5% 0.169 22.3%

RO 1.694 62.5% 1.620 78.8% 1.598 81.5% 1.583 9.9% 1.578 78.9% 1.570 16.4%

Connection 0.115 4.2% 0.049 2.4% 0.032 1.7% 0.021 3.0% 0.016 0.8% 0.014 1.9%

Total 2.710 2.054 1.961 2.022 2.000 1.911

Septic tank Daily treatment capacity (m3)

15 50 100 200 300 450

Coagulation 0.001 0.0% 0.001 0.1% 0.001 0.1% 0.001 0.1% 0.001 0.1% 0.001 0.1%

RSF 0.411 26.3% 0.073 6.6% 0.056 5.3% 0.134 12.3% 0.116 11.0% 0.077 7.6%

UF 0.141 9.0% 0.064 5.8% 0.151 14.2% 0.107 9.8% 0.092 8.7% 0.102 10.0%

RO 0.714 45.7% 0.856 77.8% 0.844 79.3% 0.839 77.0% 0.810 76.9% 0.830 81.9%

Connection 0.296 19.0% 0.106 9.7% 0.012 1.1% 0.009 0.8% 0.035 3.3% 0.004 0.4%

Total 1.563 1.100 1.064 1.089 1.054 1.014

POTW Daily treatment capacity (m3)

15 50 100 200 300 450

RSF 0.116 26.4% 0.035 10.4% 0.026 8.2% 0.041 12.3% 0.040 11.9% 0.026 8.3%

UF 0.028 6.5% 0.028 8.5% 0.028 8.8% 0.028 8.5% 0.028 8.6% 0.028 8.9%

RO 0.263 59.6% 0.263 78.2% 0.263 81.4% 0.263 78.4% 0.263 79.0% 0.263 82.4%

Connection 0.034 7.6% 0.010 3.0% 0.005 1.6% 0.003 0.8% 0.002 0.5% 0.001 0.4%

Total 0.441 0.336 0.322 0.335 0.332 0.318

Surface discharge Daily treatment capacity (m3)

15 50 100 200 300 450

Total 0.036 0.011 0.008 0.004 0.003 0.002

HT + POTW Daily treatment capacity (m3)

15 50 100 200 300 450

Coagulation 0.005 0.6% 0.002 0.4% 0.001 0.3% 0.001 0.2% 0.001 0.2% 0.001 0.2%

RSF 0.116 14.6% 0.046 9.9% 0.027 6.8% 0.044 11.5% 0.042 11.1% 0.027 7.6%

UF 0.028 3.6% 0.028 6.2% 0.028 7.3% 0.028 7.4% 0.030 8.1% 0.030 8.4%

RO 0.263 33.0% 0.273 59.5% 0.268 68.4% 0.273 71.2% 0.271 72.4% 0.271 77.0%

Connection 0.384 48.2% 0.110 23.9% 0.068 17.3% 0.037 9.6% 0.031 8.2% 0.024 6.8%

Total 0.796 0.458 0.392 0.383 0.375 0.352

HT + Surface discharge Daily treatment capacity (m3)

15 50 100 200 300 450

Coagulation 0.005 1.2% 0.002 1.4% 0.001 1.5% 0.001 1.6% 0.001 1.6% 0.001 1.9%

RSF 0.000 0.1% 0.011 7.9% 0.000 0.4% 0.003 5.5% 0.002 4.5% 0.000 0.9%

UF 0.000 0.0% 0.000 0.0% 0.003 3.5% 0.000 0.0% 0.002 3.8% 0.001 3.3%

RO 0.035 8.9% 0.011 8.6% 0.012 15.0% 0.015 29.0% 0.015 33.0% 0.011 32.1%

Connection 0.353 89.8% 0.110 82.2% 0.062 79.5% 0.034 63.9% 0.026 57.0% 0.022 61.8%

Total 0.392 0.0% 0.133 0.0% 0.077 0.0% 0.053 0.0% 0.045 0.0% 0.035 0.0%

76

8 Conclusions

Based on the costs calculated, the cost-efficiency of different water treatment unit processes at a small

scale has been steadily improving throughout the years. The extent to which this improvement occurred

depends on the unit process taken into account and the time interval considered. Compared with the

costs of the same processes in the 90’s, there have been decreases ranging from 10 to 90%. The

highest decrease in costs was verified in the RO membrane technology, its costs decreased by five,

ten-fold in a time interval of two, three decades.

The most economical water treatment solution at a small scale depends highly on the daily treatment

capacity, the residual management requirements and the raw water quality. In the presence of raw water

of good quality, which is defined by having low overall contamination levels and no specific concerning

pollutants such as nitrates or arsenic, the most economical solution, regardless of the daily treatment

capacity and the type of residual management solution chosen, consists of a compact conventional

treatment that includes elementary processes such as coagulation, pressure sand filtration and gaseous

chlorine. On the contrary, when the raw water is of a very bad quality and requires treatment processes

such as ion exchange or activated alumina to address specific pollutants, the most economical solution

differs. In such situation, for daily treatment capacities under 50 m3/day, the most economical solution

consists of a RO filtration system, regardless of the type of residual management solution chosen. For

higher treatment capacities, up to 450 m3/day, depending on the residual treatment, the most

economical solution may be either the conventional system or the RO filtration system. Somewhere in

treatment capacity range of 50-200 m3/day, the conventional water treatment alternative becomes more

economic if an expensive residual treatment alternative, such as evaporation ponds and septic tanks, is

required. Also, somewhere in the 300-450 m3/day range, the conventional alternative becomes cheaper

than the RO filtration system if cheaper residual treatment alternatives, such as the use of holding tanks

together with either surface or public owned treatment work discharges, are chosen. Lastly, if the

residual treatment alternative choice falls on surface discharge, in the presence of raw water with bad

quality, the RO filtration system is always cheaper than the conventional treatment.

To conclude, during the development of this document, it was noticed that there is no scientific work in

the literature regarding the costs of water treatment solutions as a function of raw water quality and this

document should incite other authors to adopt a similar, more general approach to the problem so that

the state of the art of water treatment systems is better understood. On the other hand, a more

comprehensive cost analysis might be developed based on a more refined raw water classification

system. The cost analysis could be further deepened through the cost estimation of other unit processes

that were not included and further refined by using component prices calculated through a statistically

significant amount of samples and through further unit cost breakdown. Also, since the cost analysis

was based on the Portuguese legal framework, the cost analysis based on a similar approach while

using different classification systems based on the legal framework of other countries is encouraged.

77

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Appendix A – Thesis defense slides and

commentary

Figure A.1 – Slide Nº 1 – Cover slide

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Figure A.2 – Slide Nº 2 – Presentation outline

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Figure A.3 – Slide Nº 3 – The water quality problem

Commentary: From the 1.8 billion people that suffer from lack of potable water, it is known that,

as suprising as it may seem, some live in developed countries. In these countries, it is common

for people that live in regions far from huge urban centers to suffer from lack of potable water.

This is due to the fact that, not only these regions do not have a population large enough to make

an efficient large-scale water treatment plant viable, but also because of the fact that, since they

are located far from a urban center, the costs of connecting these low populated regions to the

treatment plants located close to urban centers is often prohibitive. This situation led to the search

water treatment alternatives. One of these alternatives are small scale water treatment plants.

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Figure A.4 – Slide Nº 4 – The purpose of the research

Commentary: Two questions may be asked as a result of the recent decline of the investment

cost in small-scaled water treatment solutions: How much do they cost now? What are the most

economical water treatment solutions?

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Figure A.5 – Slide Nº 5 – First step of the method

Commentary: The first step consisted of comparing two documents of the Portuguese legislation.

One of them concerning the classification of the raw water according to its pretended uses, and

the other one regarding the water quality that must be guaranteed when the water is destined for

human consumption. This comparison allowed the establishment of a preliminary water

classification system that was rather incomplete in the values of the water parameters that it

defined. As such, this preliminary classification system was completed using the water quality

guidelines established by the World Health Organization.

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Figure A.6 – Slide Nº 6 – Classification system table

Commentary: The different water quality parameters were divided into three different groups as it

is shown by the different colours. Each parameter has a corresponding target parametric value

that must be complied with. Also, each parameter is classified according to three different classes

(A1, A2 and A3). Each class has a pollutant removal efficiency value for each parameter that must

be achieved in order to comply with the target parametric values required for human consumption.

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Figure A.7 – Slide Nº 7 – Second step of the method

Commentary: The second step consisted of characterizing the different water treatment unit

processes in terms of their pollutant removal efficiencies and costs. The costs were calculated

using EPA’s Work Breakdown Structure models. EPA provides, at their website, three models

that can be readily used to calculate the costs for three different unit processes (Granular

activated carbon, multi-staged bubble aeration and packed tower aeration). The remaining unit

processes were calculated based on the same framework and on the same assumptions. As for

the pollutant removal efficiencies of the unit processes, they were taken from the scientific

literature. There are many authors that have assessed the pollutant removal efficiencies of

different unit processes in both pilot-scale and large scale treatment plants.

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Figure A.8 – Slide Nº 8 – Third step of the method

Commentary: The third step consisted of combining the different unit processes, based on their

pollutant removal efficiencies, into water treatment schemes in order to reach a removal efficiency

that would be able to treat water of different qualities.

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Figure A.9 – Slide Nº 9 – Water treatment scheme matrix

Commentary: Each side of the water treatment matrix corresponds to a group of pollutants. Each

group classifies the level of contamination according to three different classes. Each cell of the

matrix has two different treatment alternatives. The first alternative was the one that was

established through the combining of the different unit processes in order to reach certain

pollutant efficiencies defined by the water classification system. Since the first alternative has a

considerable number of different unit processes, a second treatment alternative was conceived

in order to be compared with the first one in terms of investment costs. This second alternative

includes reverse osmosis, which is a unit process capable of removing virtually any pollutant.

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Figure A.10 – Slide Nº 10 – Water treatment scheme matrix

Commentary: By combining the cost models established for each unit process, and by taking into

account both treatment alternatives established for the treatment of water, the water treatment

investment costs were then calculated and combined into a treatment costs matrix.

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Figure A.11 – Slide Nº 11 – Results and discussion

Commentary: The results and discussion section was divided into two different parts, each one

of the concerning one of the questions asked in the beginning. In the first part, the costs for the

two main groups of unit processes (filtration and disinfection) will be shown and compared with

different values found throughout the scientific literature.

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Figure A.12 – Slide Nº 12 – Costs of the filtration unit processes

Commentary: For the low end of daily treatment capacities (15 m³), it seems that slow sand

filtration is the cheapest alternative. On the other hand, it seems that costs for this treatment

capacity range from about 1.5 to 2 €/m³. As for the high end of daily treatment capacities (450

m³), the cheapest alternative are rapid sand filtration and bag filtration. At this value of treatment

capacity, most of the costs for the unit processes range from 0.1 to 0.2 €/m³.

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Figure A.13 - Slide Nº 13 – Comparison of the costs of two filtration unit processes.

Commentary: The costs that were calculated for both diatomaceous earth filtration and slow sand

filtration were compared with values found in the scientific literature. The blue bar represents the

values found and the orange bar represent the values calculated. It is obvious that the value for

both unit processes has decreased.

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Figure A.14 – Slide Nº 14 – Cost of disinfection unit processes

Commentary: For the low end of daily treatment capacities (15 m³), it seems that ozonization is

the cheapest disinfection alternative. This unexpected value is a result of the ozonization system

considered in the cost analysis. Instead of using a huge commercial ozonizator that requires pure

oxygen as its main input, a more compact and efficient solution that used dry atmospheric air as

its input was chosen. On the other hand, it seems that costs for this treatment capacity range from

about 1.5 to 2 €/m³. At the high end of daily treatment capacities (450 m³), most of the costs for

the disinfection unit processes range from 0.05 to 0.10 €/m³.

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Figure A.15 – Slide Nº 15 – Results and discussion – Part I

Commentary: The costs that were calculated for chlorination, UV disinfection and chlorine dioxide

were compared with values found in the scientific literature. The blue bar represents the values

found and the orange bar represent the values calculated. It is obvious that the value for both unit

processes has decreased. It is interesting to see that, in the case of chlorination and UV

disinfection, the calculated costs were much higher than the ones taken from the scientific

literature. It is suspected that this happened because of the different cost assumptions that EPA

considered in their models 20 years ago. Since EPA also developed the WBS models, which were

the models used to calculated the costs of the different unit processes, it is suspected that the

calculated costs are more realistic because they reflect the continuous improvement that EPA’s

models have undergone in the past 20 years.

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Figure A.16 – Slide Nº 16 – Results and discussion – Part II – Comparison of both

treatment alternatives

Commentary: The first table (the colourful one) represents the costs for the first alternative. The

second table represents the costs for the second alternative. The difference in size and data

between both tables is due to the fact that the treatment scheme used in the first alternative and

the amount of reagents that are required for the water treatment vary according to the water

quality. In the case of the second alternative (reverse osmosis), the treatment scheme is always

the same.

In the first table, the lowest cost is in green and the highest cost is in red. It is possible to see that

an increase in either the concentration of heavy metals or pathogenic microorganisms doesn’t

increase the water treatment cost as much as an increase of organic compounds does.

If both tables are compared, it seems that the second alternative is always cheaper than the first

alternative. While the lowest value for the first alternative is somewhere around 6.3 €/m³, the

lowest value for the second alternative os somewhere around 3.4 €/m³. However, in the next

slides, it will be seen that this is not always the case, and the first alternative might be, in fact,

cheaper in most situations.

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Figure A.17 – Slide Nº 17 – Cell cost breakdown

Commentary: If the costs of the first alternative are broken down, it is possible to see that three

processes are responsible for 70% of the costs. These processes are ion exchange, activated

alumina and granular activated carbon. It is reasonable to assume that are situations where a

water doesn’t require any of these treatments and it is possible to exclude them from the treatment

scheme. So, what happens if we reduce the costs of the first alternative by 70%, include the costs

of the residual treatment alternatives in both treatment alternatives, and compare the resulting

costs? (See next slide.)

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Figure A.18 – Slide Nº 18 – Comparison of both alternatives when costs of the first

alternative are reduced

Commentary: The tables compares both alternatives in terms of costs for different residual

treatment alternatives chosen. The tables are arranged in increasing cost of residual treatment.

It seems that, if we reduce the costs by 70%, the first alternative is always cheaper when

compared with second one, regardless of the type residual treatment alternative included. The

cheaper cost among both alternative is represented in green. It is possible to see that the values

for the first alternative are always in green. Now, what happens if the treatment cost values for

the first alternative aren’t reduced by 70%? (See next slide.)

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Figure A.19 – Slide Nº 19 – Comparison of both alternatives with no cost reduction

Commentary: If the water treatment costs of the first alternative aren’t reduced by 70%, it seems

that, for the cheapest residual treatment alternatives (surface discharge, public owned treatment

work and holding tank + surface discharge), the second water treatment alternative is cheaper,

regardless of the daily treatment capacity. However, when more expensive residual treatment

alternatives are considered, there’s a shift between both alternatives. The more expensive a

residual treatment alternative is, the smaller the range of daily treatment capacities, where the

second alternative is cheaper, becomes.

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Figure A.20 – Slide Nº 20 – Conclusions

Commentary: Regarding the first question, it is possible to affirm that, based on the results, the

investment costs of the unit processes have decreased from 30 to 70%. Their unit cost usually

ranges from 1.5 to 2 €/m³ for a daily treatment capacity of 15 m³. For a treatment capacity of

450 m³, the costs range from 0.05 to 0.20 €/m³.

Regarding the second question, it seems that, when the water is of a lower quality, reverse

osmosis is the best option if the costs with residual treatment are relatively low. If the residual

treatment costs are high, reverse osmosis is only cheaper than a conventional treatment for lower

daily treatment capacities. In the case of treating a water of a higher quality, a conventional

treatment is better than reverse osmosis, regardless of the daily treatment capacity required and

the residual treatment alternative chosen. This happens due to the fact that the conventional

treatment alternative is more flexible and can be more tailored, and, as such, very specific

solutions can be composed and the costs reduced.

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