Determination of Domestic Wastewater
Transcript of Determination of Domestic Wastewater
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DETERMINATION OF DOMESTIC WASTEWATER
CHARACTERISTICS AND ITS RELATION TO THE TYPE AND SIZE OF
DEVELOPMENTS.
SOHAIMI KLING
A project report submitted in partial fulfillment of the
requirements for the award of the degree of
Master of Engineering
Faculty of Civil Engineering
Universiti Teknologi Malaysia
MAY 2007
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I declare that this thesis entitled “ Determination of Domestic Wastewater
Characteristics and Its Relation to the Type and Size of Developments ’ is the result
of my own research except as cited in the references. The thesis has not been
accepted for any degree and is not concurrently submitted in candidature of any
other degree.
Signature : ………………………………………….
Name : ………………………………………….
Date : ………………………………………….
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To my beloved wife, sons and daughters
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ACKNOWLEDGEMENT
In preparing this thesis, I was in contact with many people including
academicians and practitioners. They have contributed towards my understanding
and thoughts. In particular, I wish to express my sincere appreciation to my main
thesis supervisor, Professor Dr. Ir. Mohd.Azraai Kassim and all lecturers especially
Professor Dr. Razman Salim, Professor Madya Dr. Fadil Othman and Dr. Azmi Aris
for their guidance, advices and motivation. Without their continued support and
interest, this thesis would not have been the same as presented here.
I am also indebted to my employer Indah Water Konsortium Sdn Bhd for
funding my study. Librarians and other staff at UTM and IWK also deserve special
thanks for their assistance in supplying the relevant literature.
My sincere appreciation also extends to all my colleagues and others who
have provided assistance at various occasions. Their views and opinions are useful
and unfortunately, it is not possible to list all of them in this limited space. I am
grateful to my family particularly to:
Rihanah Ahmad
‘Umayr Hasan Sohaimi
Muhammad Suhail Sohaimi
Ahmad Naufal Sohaimi
Syakir Husein Sohaimi
‘Ali Jabri Sohaimi
Faris Muhsin Sohaimi
Zaid Harith Sohaimi
Nur Safiah Sohaimi
Yusuf Fadhli Sohaimi Nur Khodijah Sohaimi
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ABSTRACT
Ciri-ciri air-sisa domestic mentah di negara ini kini ditetapkan berdasarkan
kepada dua (2) parameter utama iaitu; 250 mg/l BOD and 300 mg/l SS bagi
merekabentuk kemudahan Logi Rawatan Kumbahan (STP) , sepertimana yang
digariskan di dalam MS 1228. Suatu semakan telah dilakukan terhadap standard
efluen ini, yang membahagikan STP kepada tiga (3) kategori iaitu:-
Kategori 1 yang ditetapkan kepada semua STP yang diluluskan setelah tarikh
had baru efluen digazetkan;
Kategori 2 ditetapkan kepada semua STP yang diluluskan selepas
penguatkuasaan 'Guidelines for Developers, Sewage Treatment Vol. 4
(GDV 4), 2nd Edition' yang dikeluarkan olih Jabartan Perkhidmatan
Pembetungan mulai Januari 1999;
Kategori 3 ditetapkan kepada semua STP yang diluluskan sebelum GDV 4
dikuatkuasakan.
Yang demikian, logi baru dibawah Kategori 1 (satu) hendaklah di rekabentuk bagi
mecapai samaada Standard A atau B dibawah semakan standard rekabentuk yang
baru. Bagaimanapun, tidak banyak kajian yang telah dilakukan untuk mengesahkan
ciri-ciri air-sisa domestic mentah berdasarkan kondisi setempat. Suatu tahap
rekabentuk optima akan dapat dihasilkan jika komposisi dan ciri-ciri air-sisa
domestic ditentukan dengan lebih jelas. Dengan menjalankan kajian ini, suatu
pemahaman yang lebih baik akan dapat diperolehi mengenai ciri-ciri air-sisa
domestic yang tipikal, dengan mengenalpasti air-sisa yang berpunca daripada
pelbagai jenis pembangunan (kediaman, perdagangan, perindustrian dan
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pembangunan bercampur). Selain itu, kajian ini, akan seterusnya menentukan
perbezaan ciri-ciri air-sisa bedasarkan pembangunan dengan saiz yang berbeza. Ini
akan menjadi asas kepada penetapan garispanduan akan datang, yang boleh
mendorong kepada penambahbaikan serta menghasilkan rekabentuk optima bagi
proses rawatan air sisa domentik.
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ABSTRACT
Currently, the characteristics of raw domestic wastewater in the country
adopted two (2) main parameters i.e. 250 mg/l BOD and 300 mg/l SS in the design
of Sewage Treatment facilities, as spelt out in MS 1228.
A new revised effluent discharge standard will categorise all STPs into three
categories:
Category 1 applies to all STP approved after the gazette date of the new
effluent discharge limits;
Category 2 applies to all STP which were approved after the 'Guidelines for
Developers, Sewage Treatment Vol. 4 (GDV 4), 2nd Edition' was enforced
by Department of Sewerage Services beginning January 1999;
Category 3 applies to all STP, which were approved before GDV 4 was
enforced.
Hence, new plants under Category 1(one) shall be designed to meet either Standard
A or B under the new revised design standards. However, not many studies have
been carried out to validate the characteristics of raw sewage based on local
conditions. An optimal design of sewage treatment can be established if the
composition and the characteristics of domestic wastewater are clearly determined.
By initiating this study, a better understanding on the typical characteristics of raw
domestic wastewater can be obtained that will also identify the domestic wastewater
generated from various types of developments (residential, commercial, industrial
and mixed development. Likewise, this study will further verify the difference of
raw sewage constituents that originated based on different sizes of the
developments. This will serve as a guide for future adoption that will help to
improve and optimize design of domestic wastewater treatment processes
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
TABLE OF CONTENTS viii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF ABBREVIATIONS xii
LIST OF SYMBOLS xiii
I INTRODUCTION
1.1 Background 1
1.2 Objectives of the Study 3
1.3 Scope of Study 3
II LITERATURE REVIEW
2.1 Domestic wastewater generation 5
2.2 In-pipe treatment 11
2.3 Water consumption, norms, ethnic and religious
practices 132.4 Effect of trade wastewater into sewer 15
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2.5 Environmental and hydraulic influences 16
2.6 Sediments in sewer pipe 19
III METHODOLOGY
3.1 Analysis of all influent sampling data 21
3.2 Analysis of influent sampling data from
different type of developments 21
3.3 Analysis of influent sampling data from
different size of developments 22
3.4 Sampling 22
3.5 Elimination of outliers 23
IV RESULTS AND DISCUSSION
4.1 Mean and percentile value of overall samples 24
4.1.1 Mean and percentile value of BOD 24
4.1.2 Mean and percentile value of COD 26
4.1.3 Mean and percentile value of AMN 27
4.1.4 Mean and percentile value of SS 29
4.1.5 Mean and percentile value of pH 30
4.2 Mean wastewater characteristic based on
type of developments 32
4.3 Mean wastewater characteristic based on
size of developments 36
V CONCLUSIONS
5.1 Wastewater characteristics based on the
overall analysis 44
5.2 Recommendations 46
REFERENCES 47
Appendices 51
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LIST OF TABLES
TABLE NO TITLE PAGE
Table .1.1 Proposed revised effluent discharged standard
for Category 1 STP 2
Table 2.1 Typical Characteristics of Untreated Domestic
Wastewater 7
Table 2.2 Mean Results of Domestic Wastewater
Characteristics 10
Table 4.1 Characteristics of Domestic wastewater from
all Samples 32
Table 4.2 Mean Domestic wastewater characteristics
based on type of Developments 34
Table 4.3 Size of Development- Mean Domestic
wastewater characteristics 37
Table 5.1 Characteristics of Domestic wastewater from
all Samples 45
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LIST OF FIGURES
TABLE NO TITLE PAGE
Figure 4.1 BOD Concentration range 25
Figure 4.2 BOD Percentile 25
Figure 4.3 COD Concentration range 26
Figure 4.4 COD Percentile 27
Figure 4.5 AMN Concentration range 28
Figure 4.6 AMN Percentile 28
Figure 4.7 SS Concentration range 29
Figure 4.8 SS Percentile 30
Figure 4.9 pH Concentration range 31
Figure 4.10 pH Percentile 31
Figure 4.11 Mean Domestic wastewater characteristics
based on type of Developments 35
Figure 4.12 Mean Domestic wastewater characteristics
by size of Developments 38
Figure 4.13 BOD variation with increase of development size 39
Figure 4.14 COD variation with increase of development size 40
Figure 4.15 AMN variation with increase of development size 41
Figure 4.16 SS variation with increase of development size 42
Figure 4.17 pH variation with increase of development size 42
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LIST OF ABBREVIATIONS
A/ITI - Alkalinity
AMN - Ammonical Nitrogen
BOD - Biochemical Oxygen Demand
COD - Chemical Oxygen Demand
DOE - Department of Environment
GDV - Guidelines for Developers
IWK - Indah Water Konsortium
MS - Malaysian Standard
PE - Population Equivalent
pH - Hydrogen-ion concentration
SS - Suspended Solid
SSD - Department of Sewerage Services
STP - Sewage Treatment Plant
UTM - Universiti Teknologi Malaysia
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LIST OF SYMBOLS
mg/l Milligram per litre
l/p/d Litre per person per day
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CHAPTER I
INTRODUCTION
1.1 Background
The Environmental Quality Act 1974 specifies two standards of effluent
discharges i.e. Standard A for discharges upstream of raw water intakes and
Standard B for discharges downstream of raw water intakes. A new revised effluent
discharge standard will categorize all STPs into three (3) categories in accordance to
the type of plants and the date when the design is approved:
Category 1 applies to all STPs approved after the gazette date of the new effluent
discharges limits;
Category 2 applies to all STPs which were approved after the 'Guidelines for
Developers, Sewage Treatment Vol. 4 (GDV 4), 2nd Edition' was enforced by
Department of Sewerage Services beginning January 1999;
Category 3 applies to all STPs, which were approved before GDV 4 was
enforced.
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Therefore, new plants under Category 1 shall be designed to meet either Standard A
or B based on compliance to the proposed revised effluent standard in Table 1.1
shown below.
Table 1.1: Proposed revised effluent discharge standard for Category 1 STP.
Parameter(mg/l )
Effluent Discharge toRiver/Stream
Effluent Discharge toStagnant Water Bodies**
Standard A Standard B Standard A Standard B
BOD 5 20 50 20 50
SS 50 100 50 100
COD 120 200 120 200AMN 10 20 5 5
Nitrate Nitrogen
20 50 10 10
Phosphorus na na 5 10
O&G 5 10 5 10
Notes: na = Not Applicable
**Stagnant Water Bodies refer to enclosed water bodies such as lakes, ponds
and slow moving watercourses where dead zones occur.
Currently, data with regards to the characteristics of raw sewage in the country is
based on MS 1228, which emphasizes on 2 main parameters i.e. 250 mg/l BOD, and
300 mg/l SS as design parameters. However, no local in-depth studies have been
carried out to verify the characteristics of raw sewage in the country.
Differences in the constituents that are generated from various types of development
have not been determined to observe its significance. Similarly, no record has ever
been initiated to determine the variables that influence the domestic wastewater
generated from difference sizes of developments. Estimation of wastewater
characteristics is necessary to determine the design capacity of the treatment plant.In
case of new development projects where the actual wastewater data is not available,
the wastewater loading and flowrates are derived from population estimates and the
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wastewater load and composition are solely based on the locally accepted typical
values.
By initiating this study, a better understanding on the typical characteristics of raw
sewage can be obtained that will help to improve design of sewage treatment
processes.
1.2 Objectives
The objectives of this study are as follows:-
To determine the ranges of typical composition of raw sewage in terms of BOD,
SS, COD, AMN, and pH values.
To study the typical characteristics of raw sewage generated from various types
of developments in the country i.e. from residential, commercial and from mixed
developments.
To identify the typical raw sewage measured in relation to the size of the
developments.
1.3 Scope of study
The study is based on data of periodical influent sampling results generated
from year 2003 to 2005 at all sewage treatment plants in the country. The study does
not include a 24 hours sampling to gauge the diurnal fluctuation pattern in the
concentration load.
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Although the data are gathered based on grab sampling carried out during half-
periods of the weekday, yet it involved an extensive representation in samplings
with a total number of approximately 30,000 samples, and cover a broad span in
terms of locations, numbers, type and size of developments.
This study however, does not include Phosphorous and Oil &Grease constituents in
the domestic wastewater.
Likewise, this study does not include treatment processes applied to meet the
prescribed effluent standards.
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CHAPTER II
LITERATURE REVIEW
2.1. Domestic wastewater generation
Domestic wastewater by definition is the discharge from domestic residences,
commercial or industrial premises into the public sewer, originated from all aspects
of human sanitary water usage. It typically constitutes a combination of flows from
bathroom, toilets, floor traps, kitchen sinks, dishwashers and washing machines.
However, apart from domestic wastewater originated from residence, other premises
such as commercial, institutional and industrial also contribute a domestic
wastewater component to the sewer system. In Malaysia, a separate sewerage
conveyance system is adopted from the domestic use only and do not combine with
either storm water or industrial process wastewater.
Adoption of design parameters for biological process design is difficult because
domestic wastewater concentration vary greatly from one country and one
community to another for various reasons, such as differences in food consumed,
water use and personal hygiene practices. Hence, the average daily rates of flow
generation are also dependent significantly on the socio-economic status of the
community particularly with respect to its affluence and standard of living.
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The most accurate way to determine the character and quantity of domestic
wastewater is to measure the existing wastewater flow over a sufficient length of
time to determine its variability in terms of composition, concentration and load.
However, in the case of new development, a prescribed wastewater flow and typical
characteristics of the domestic wastewater need to be adopted for the design stage of
a new treatment system in meeting with the stipulated discharge standard.
There were literature that outlined the typical influent characteristics of domestic
wastewater studied elsewhere and one which is widely refered to is tabulated in
Table 2.1.
The treatment of sewage will require the processing of both organic and inorganic
solid matter as explained by Rendell (1999). This matter will be in the form of
dissolved solids and suspended solids. The inorganic load is comprised of grits and
salt. Sewage with high industrial waste element will consist of compounds and
possibly include highly toxic chemicals. To enable the nature of the liquid to be
described there is a need to define two things: firstly a characteristic that reflects the
nature of the compound and secondly, its concentration in the solution. The
concentration will be expressed in terms of mass per unit volume The more usual
units is mg/l. Another form in which the quantity of a compound will be expressed is
a load. This type of unit is used to define loadings on the system and is calculated
from concentration and the flowrate e.g gm per day.
The characterization of domestic wastewater involves an examination of all essential
elements of wastewater characterization; namely its typical composition in terms of
BOD, SS, COD, AMN and pH. BOD 5 is used to measure the biodegradable organic
fraction in raw sewage.
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Table 2.1: Typical Characteristic of Untreated Domestic Wastewater
ConcentrationContaminants Unit
Weak Medium Strong
Solids, total (TS) mg/L 390 720 1230Dissolved, total (TDS) mg/L 270 500 860
Fixed mg/L 160 300 520
Volatile mg/L 110 200 340
Suspended solids (SS) mg/L 120 210 400
Fixed mg/L 25 50 85
Volatile mg/L 95 160 315
Settable solids mg/L 5 10 20BOD 5, 20°C mg/L 110 190 350
Total organic carbon mg/L 80 140 260
COD mg/L 250 430 800
Nitrogen (total as N) mg/L 20 40 70
Organic mg/L 8 15 25
Free ammonia mg/L 12 25 45
Nitrites mg/L 0 0 0 Nitrates mg/L 0 0 0
Phosphorus (total as P) mg/L 4 7 12
Organic mg/L 1 2 4
Inorganic mg/L 3 5 10
Chlorides mg/L 30 50 90
Sulfate mg/L 20 30 50
Oil and Grease mg/L 50 90 100Volatile organic
compound
mg/L 400
Total Coliform #/100mL 10 6~10 8 107~10 9 107~10 10
Fecal Coliform #/100mL 10 3~10 5 104~10 6 105~10 8
Source: Metcalf and Eddy .Wastewater Engineering, Treatment and Reuse.
4th Edition. 2004. Table 3-15.
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In the standard measurement of BOD 5, the oxygen demand measured is influenced
by three conditions: (a) Oxygen demand by the breakdown of soluble carbonaceous
matter (b) Oxygen demand by the breakdown of suspended particulate carbonaceous
matter (c) Oxygen demand by the oxidation of ammonia to nitrate by nitrifying bacteria present in the effluent sample. As the amount of residual soluble
carbonaceous BOD 5 matter in the effluent, after undergoing treatment in the
secondary reactor, reduces in concentration to below 15 mg/l, nitrifying bacteria
populations tend to grow rapidly feeding on ammonia present in the partially treated
sewage. Nitrification may not be complete at levels of 5 mg/l of residual soluble
carbonaceous biodegradable matter; it depends on whether sufficient oxygen is
available for oxidation of ammonia to nitrate.
BOD is used not only to indicate the strength of a wastewater but also that of a
treated effluent and the efficieny of the various stages of treatment. The BOD of
domestic sewage may be expected to lie in the range of 150 to 600 mg/l whereas for
industrial wastes values from 0 to 100,000 mg/l may be found, depending upon the
nature of the industry. (Pescod, 1999)
Sewage also contains solid material that can settle on the bottom or in suspension
solids form that can increases turbidity and impact the light availability for aquatic
life. The desired solids removal in sewage treatment should reflect the absolute SS
discharge limit of 50mg/l and 100mg/l for Standard A and Standard B catchment.
COD content reflects the chemically oxidized organic matter; hence it includes
refractory fractions of organic matter as well as reduced inorganic constituents
present in the wastewater. The measure of COD offers a quick estimate of
carbonaceous material compared to conventional BOD measurements. Additionally,
high COD reflects the potential industrial contamination in the form of inert reduced
inorganic elements and unbiodegradable organics. Based on the bisubstrate
hypothesis, COD fractions of readily biodegradable, slowly biodegradable and
unbiodegradable estimates are also adopted in advanced modeling for STP design
whereby the different fractions vary in susceptibility to microbial respiration and
degradation.
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Wastewater may contain high levels of nutrients. Excessive release to the
environment can lead to a build-up of nutrients, i.e. eutrophication, which can in turn
encourage the overgrowth of algae. Not just an aesthetic issue, some algal species
produce toxins which contaminate drinking water supplies, while in serious cases, so
much algal/plant matter can be present that the consumption of dead plant matter by
bacteria decay depletes the oxygen in the water and suffocates fish and other aquatic
life. Removal of nitrogenous compounds needs to be considered in STP design. It is
found in varying forms that are detrimental to natural water bodies and potable
consumption. To ensure compliance with the prescribed effluent discharge standard,
the characteristic of the nitrogenous constituent shall be determined in order that
adequate nitrifications and denitrification in the secondary biological reactors design
is provided. (Sewerage Services Department, 1998).
The hydrogen-ion concentration, which is expressed as pH, is an important
parameter for wastewater as a suitable concentration range allows for the survival,
growth and existence of most biological life. For carbonaceous removal, pH in the
range of 6 to 9 is tolerable, while optimal performance occurs near a neutral pH.
Nitrification is affected by a number of environment factors and the rates declined
significantly at pH values below 6.8. Optimal nitrification rates occur at a pH range
of 7.5 to 8.0. Alkalinity is produced in denitrification reactions and the pH is
generally increased instead of being depressed as in nitrification reactions. In
contrast to nitrification, there has been less concern about pH influence on
denitrification rates. Wastewater with an extreme concentration of hydrogen ion is
difficult to treat by biological means, and if the concentration is not altered before
discharge, the wastewater effluent may alter the concentration in the natural
waterbody.
Collaborative research between IWK and UTM (Othman,2003) was conducted to
determine the per capita loading and water consumption in sewage treatment design.
Six (6) different sites were identified with PE ranging from 1,000 to 20,000. For
each site, a full 14-day study was done. Composite as well as 24 hours sampling
were carried out for the first 3 days and 4 times per day for the next 11 days and the
result is tabulated in Table 2.2 below.
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recommended that for sewerage system design purposes it can be assumed that a
single person resident generates an average daily sewage flow of 225 litres per day.
The inherent wastewater load will also change due to changed diet habits e.g.
consumption of more processed food and use of kitchen grinder/macerator for
disposal of scrap food into sewerage system. Also, a tendency for using household
chemicals which include detergent and cleaning agents increased the amount of less
degradable materials into the sewer. Determination of wastewater characteristic and
concentration is necessary to ensure that the design capacity as well as the process
requirements of the treatment plant is fulfilled. The availability of the actual flow
and loading pattern will lead to a better design and ways of operating the STP
facility.
2.2. In-pipe treatment
Tanaka et al.(2000) reported that microbial transformation of organic matter in
wastewater takes place during transport in sewers. These processes occur in the bulk
water phase, in biofilms, and in temporarily settled sediments under aerobic and
anaerobic conditions .Under aerobic conditions in a gravity sewer, readily biodegrad-
able substrate, either directly discharged to the sewer or originating from
hydrolysable substrate, is removed, and biomass is produced .
On the same note Vollertsen et al (2005),clarified that wastewater quality undergoes
changes when conveyed in sewers. How and to what extent such changes occur
depends on the physical, chemical, and microbial conditions in the sewer as well as
the composition of the wastewater. Under aerobic conditions, the sewer biomass
consumes easily biodegradable organic matter, resulting in a wastewater improved
for mechanical and chemical treatment. On the other hand, when conditions become
anaerobic, the biomass consumption of readily biodegradable substrate is
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considerably reduced and fermentation of organic matter will result in a more easily
biodegradable wastewater.
Boon (1995) further testified that septicity in sewerage systems results from the
activity of bacteria, growing in sewage and on submerged surfaces which, under
anaerobic conditions, reduce sulphur-containing organic compounds and sulphates
to form sulphides and other malodorous sulphur compounds.Lack of adequate
ventilation, low velocity of sewage in large diameter sewers or small diameter rising
mains and high temperature, BOD or COD of sewage, will inevitably result in
septicity.
Balmer and Tagizadeh-Nasser (1995) in their paper states that wastewater engineers
often are heard to blame their failures on the fact that wastewaters are so different.
As long as wastewaters are predominantly of domestic origin it is however suprising
that they are different. The only rational explanation is that wastewaters are
transformed during transport from households to the wastewater treatment plant. The
per capita lengh of sanitary sewers is 3m to 10m and if the biofilm of the wetted
sewer perimeter is assumed to have the same activity as a biofilm in a trickling filter
or in a rotating biological contactor, it is obvious that a substantial part of the
organic matter in the wastewater can be metabolised before the wastewater enters
the wastewater treatment plant.The study also confirmed that energy dissipation is a
key factor for oxygen transfer in sewers.
Abdul-Talib et al (2003) hence advocated that sewer networks can and should be
designed not only for conveyance of water and pollutants, but also for obtaining a
wastewater quality that is suitable for the treatment processes at the receiving
wastewater treatment plant. It is well known that more than half of the cost to
provide a sewerage system is taken up by the sewer network. Therefore, it will be a
waste if the lengths and volumes of the sewers, which have potential treatment
capability are not fully utilised.
Conventional sewer systems in urban areas are designed and constructed in order to
transport wastewater from its source to treatment plants. During the transport of wastewater in sewer systems, many physical, chemical and biological
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transformations may result in significant changes in the wastewater composition.The
microbial transformation can be determined based on three types of conditions:
aerobic,anaerobic or anoxic, depending on the type of electron acceptors that are
present in the wastewater. Each of them produces different processes that will
change the quality of the wastewater transported upon arrival to the wastewater
treatment plants. Therefore, it is possible to design sewer systems to achieve dual
purposes: transport and biotransformation of wastewater as presented by Ujang et al
(2004). Results from a laboratory-scale sewer system as a bioreactor under tropical
anoxic condition revealed that the overall removal efficiency between 0 to 3 km
samples in the sewer system are as follows:suspended solids 58%,turbidity 24%,
COD 30% and BOD 25%.
Today, the importance of the sewerage system as a biological reactor ,in which
aerobic or anaerobic biochemical processes will occur, has been recognised. The
benefits of wastewater pretreatment under aerobic conditions can be maximised by
ensuring that sewerage systems are designed to achieve reaeration of wastewater at a
rate greater than the rate at which microorganisms (present in the wastewater and
attached to submerged surfaces in the pipework) consume dissolved oxygen.
Sewerage systems should include long gravity sewers which operate at self-
cleansing velocities, ensure adequate reaeration and include vertical-lift pumping to
avoid excessive periods of wastewater storage in the absence of adequate reaeration
(Pescod, 1999 ).
2.3. Water consumption, norms, ethnic and religious practices
There is growing realisation among water suppliers and academics that water
demand stems from routine behavior and norms which develop within a particular
social background and this has been studied by Smith and Ali (2006).This is is in
contrast to other types of consumer demand in which customers exercise consciouschoice. Despite such acnowledgement, the idea that ethnic background and religion
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may both form a fundamental basis for water consumption norms and practices is
largely overlooked.The study conducted in UK revealed that water use patterns are
highly characterised by ethnicity and religious practice.
Design Guidelines for Water Supply Systems published by the Malaysian Water
Association (1994) specified that, per capita water demand should be classified
under three categories. The guideline below gives a range of per capita consumption
for each of the three categories:
Urban-230 to 320 liters/ head/day,
Semi-Urban-180 to 230 liters/ head/day,
Rural- 135 to 180 liters/ head/day.
The design guidelines also reported that the daily demand varies slightly due to the
weather and festive seasons. In most states, daily water demand increases slightly in
the month of January and February. During festive seasons, experience has shown
that in some urban centres, there is a change in demand due to shutting down of
factories while there is an increase in demand in rural areas and smaller urban
centers due to people leaving big urban centres for their hometowns and villages.
The MS 1228 specify that sewerage systems be designed based on an average daily
per capita flow of 225 litres and the process design of a domestic waste treatment
shall be on the basis of 55 grams of BOD per capita per day and 68 grams of
suspended solids per capita per day, which equate to concentration of 245 mg/l and
302 mg/l for BOD and SS respectively
Galil and Shpiner (2001) explained the effect of kitchen sink macerator; that the
domestic garbage disposer is an electro-mechanical device which is installed
underneath the kitchen sink and is used to grind solid wastes resulting from food
preparation. The mixture of grinded solids and water is flushed to the sewerage
system and to the sewage treatment works. As a result of grinded garbage
discharged to the collection system, a change in the quality and quantity of crude
sewage is usually reported due to the addition of suspended solids, as well as theincreased water consumption for the flushing action. The disadvantages associated
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with garbage grinders are based on the fact that the solid waste is grinded and mixed
with fresh water, transforming it into wastewater, and adding to the load on the
sewerage system. This may cause deposition and clogging problems in sewers, and
can result in an additional organic loading and an increased amount of sludge.
Greywater as defined by Howarth (2002) is wastewater from sinks, baths, showers
and domestic appliances. Kitchen sink or dishwasher wastewater generally has high
levels of contamination from detergents, fats and food wastes.
The separation at source could be an option for public health protection: blackwater
from toilets is treated in individual septic tanks or small sewage plants, and the
greywater or sometimes called sullage, is discharged to the hydraulically well
designed stormwater drain, or into a sullage soakaway (Abdul-Hamid and Ujang,
2006). However, separation at source can also contribute to water pollution. In this
situation, stormwater drains contain high concentrations of washing chemicals, oil
and grease and residuals of food. Most of the stormwater drains in urban areas in
tropical countries are connected to tributaries of major rivers. As a result it is a
phenomenon that tropical rivers are mainly polluted due to untreated greywater.
2.4. Effect of Trade wastewater into sewers
Lesikar et al (2006) published literature which indicates that designers' use of
industry-accepted methodologies and design values for sizing treatment systems for
restaurants has, in the past, resulted in systems that are inadequately designed with
regard to hydraulic and organic loading A study evaluating the failure rate of two
restaurants against the mean age to failure rate for lower strength residential
wastewater treatment systems of 18 years indicates concern in allowing existing
residential-based design guidelines to be used for commercial or industrial facilities.
This is particularly true of treatment-system designs used in food-service
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establishments. Comparison of the above-mentioned studies shows that higher
wastewater strengths can induce a faster decline of treatment-system performance.
A Guide published by the Pollution Prevention Committee, Water Environment
Federation, highlighted that facilities that service vehicles, whether automobiles,
trucks, airplane, or boat have been shown to discharge heavy metals, solvents, and
oil and grease to both sanitary sewer and storm drain system. These facilities not
only include retail repair shops but also fleet maintenance operations within
organizations that exist primarily for purposes other than servicing vehicles (e.g.
delivery services and corporate fleets).Although many of these facilities, particularly
retail repair shops, may not be large, they often are numerous within a community
and have a combined effect on both sanitary sewers and storm drain
systems.(Brosseau et al, 1995)
Studies by Jenkins (1988), have demonstrated that numerous sources contribute to
the levels of heavy metals found in municipal wastewater, including the water
supply, industry and residential activities. An earlier study identified the heavy
metals contribution of household washing products compared to other sources.
2.5. Environment and Hydraulic influences
Muirhead (2005) states that microorganisms in wastewater collection systems
can affect the alkalinity and pH of wastewater. Depending on the organism, the
environmental conditions, and the biological mechanism, alkalinity can increase or
decrease and have beneficial or detrimental effects. Means by which
microorganisms can affect alkalinity and pH in wastewater collection and treatment
systems are: biological respiration, fermentation, nitrification, denitrification,
photosynthesis, sulphate reduction and sulphate oxidation. Hence, environmental
conditions in wastewater collection and treatment system can promote the growth of a wide range of microorganisms that can affect alkalinity and pH. Understanding of
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these effects can help operators optimize facilities and minimize the negative effect
on capital and operations and maintenance cost, as well as permit compliance.
Infiltration into sewer systems are contributed by factors such as (i) age of sewer, (ii)
condition of connection either direct to pipe or to manhole, (iii) illegal connection of
roof gutter and drain to sewer system, (iv) permeability of soil around sewer, (v)
groundwater elevation and (vi) quality of construction. Besides infilling during
raining season due to high water table, on the contrary will cause leakages and
diffusion of wastewater to the ground adjoining the pipeline during dry weather.
A study conducted by UTM-IWK (Norhan, 2003) at four housing estates in Johor
Bahru identified that, infiltration in many areas is as low as 88l/d per km per mm
and as high as 4700l/day per km per mm. Leakage is more than 20% of flow in most
sewers tested and in some places even reaches 8000l/d per km per mm. Leakage is
more severe during drier periods than wetter periods. In comparison, the allowance
of infiltration given in MS 1228:1991 states that infiltration sewerage system may be
designed to cater for a maximum infiltration rate of 50 litres per mm diameter per
km of sewer per day. Hence, the above study shows that the measured value of
infiltration has exceeded the permissible rate. Among the reasons for this is ageing
sewer systems and porous soil with infiltrative capacity.
Madsen et al (2006) identified that ventilation of sewer systems is important to
maintain aerobic conditions in the wastewater and to control odor and corrosion. The
following five factors have been identified as the major contributors to natural sewer
ventilation: (i) wind speed may create suction or pressure across manholes, (ii) flow
of wastewater drags the sewer gas, (iii) variations in wastewater level forces the air
into and out of the sewer, (iv) temperature differences between the sewer gas and the
urban atmosphere result in differences in gas densities and (v) differences in
atmospheric pressure lead to gas volume expansion and compression.
When planning, designing and operating a wastewater treatment plant in a warm
region, the climatic specifics must be taken into account to make best use of the
many favourable characteristics enabled by the higher temperatures. In similar way,
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for a treatment plant in a developing region, the aspects relevant to its sustainability
must be judiciously incorporated (Von Sperling and Chernicharo, 2006).
In the design of treatment process or a transfer system, the ideal condition for the
design is that the loadings should be constant. Because the limited buffering of flows
within the sewerage system (unlike buffering effect of a water service reservoir), the
design and operation of a sewerage system become more difficult due to the high
flow variation. (Rendell, 1999) The term population and water consumption are
closely linked to social changes and the way in which a community uses water. The
industrial loads have to be estimated with knowledge of the type of industry that
exists in the catchment. The daily and seasonal variation in industrial flows will be
dictated by the type of the industry and the mode of operation.
The causes of flow variation within a system are: (a) a long term variation due to
change in water use (b) the annual flow variations due to such factors as holiday
populations and seasonal industrial processes (c) weekly variation will be
predominantly caused by commercial and industrial work patterns and (d) diurnal
variation due to the normal life patterns of the domestic consumer. For a large or
widely spread sewerage system with flow within the system that have average
velocities of 0.8 m/s, thus the time between flows entering the system and arriving at
a collection point will vary greatly. The effect of this is that the system, due to its
volume, will act as a buffer and attenuate the peak flow. The contribution of
industrial wastes can be biological in nature dictated by the industrial process such
as poultry packing and dairies although the concentration is much higher.
Both turbulence in the water phase and the pH were found to play a crucial role in
the transfer of hydrogen sulfide. The air-water transfer process of hydrogen sulfide,
which also incorporates the association process, can be related to the reaeration
process in terms of their transfer rates. A relationship between the two processes is
primarily established for the pH range typical for domestic wastewater (Yongsiri et
al, 2004).
Depending on the length of sewer networks, the flow generated from source mayrequire several hours to flow through the sewer network system because of flow
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dampening effect and prolonged by the available storage capacity in the sewer
system. Intermittent inflow can also occur due to the collection and delayed
discharged via network pumping stations that is being controlled and triggered the
flow by water levels or timer which is then transferred to the downstream trunk line.
Delay inflow hence is due to the collection and discharged via network pumping
stations that transferred flow to the downstream trunk line toward the headworks of
the treatment plant.
2.6. Sediments in sewer pipes
For the provision of a new sewerlines system, it is a common practice to
provide a conservative design gravity sections which usually convey peak flows to
justify a worst case scenario for the new system. The peak flows occurrence may
happen only over a shorter period or even on instantaneous mode of the peak flow.
At minimum flow situation, the least flowrate and minimum velocity will lead to
built-up of solids in the sewer.
Rushforth et al (2003) states that the presence of sediments in sewers can cause a
number of problems for operators. Deposits of sediments in pipes can reduce
hydraulic capacity, either by reducing the flow area or increasing the hydraulic
resistence.In-sewer deposits are also believed to store pollutants which are released
when deposits are mobilized during intense storm events. Accordingly, erosion of
such deposits is thought to be responsible for sudden large increases in suspended
solids which are observed at the leading edge of storms in a number of catchments.
Sewage treatment plants are designed to flow as much as possible under gravity, in
order to minimise the number of pumps in the catchment area depending on
topography. The hydraulic processes in the pumping stations may include pumping
system hydraulics, closed conduit hydraulics and in some cases transient hydraulics.In the event of pump failures, which may be due to electrical failures, mechanical
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failures or breakdown of the pumping systems, the hydraulic processes in the
approaching sewers will change drastically. In the sewage pumping stations, the
operations are intermittent as the incoming flow varies over time according to
diurnal distribution. The intermittent operations of pumps may lead to occurrences
of transient flow and no flow conditions. This in a way will have effect to the
mobilization and deposition of sediments in the sewer pipes.
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CHAPTER III
METHODOLOGY
3.1 Analysis of all influent sampling data.
The study was conducted through analysis of an approximately 30,000 raw
influent sampling data gathered for year 2003 to 2005 representing an approximately
4,200 sewage treatment systems nationwide (with the exception of Johor Bahru city
area; states of Kelantan, Sabah and Sarawak.) The influent sampling exercises are
part of the operational monitoring requirement carried out by IWK .The sampling
frequency and visitation are principally determined by the size of the STP. All
sampling results including influent and effluent information are recorded that linked
to specific STP asset references.
3.2 Analysis of influent sampling data from different type of developments.
Another set of data was made available defining the type of customer (residential, commercial and industrial premises) that are connected to a particular
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3.5 Elimination of outliers.
Outliers were removed by eliminating data that fall within one percent of the
lowest band and also those data that fall within one percent of the uppermost bands
These data are considered extreme values that may be influenced by sudden surges
of loading due to the possibility of illegal pollution discharge from unidentified
sources or may be due to the effect of high rate infiltration that severely diluted the
raw sewage influent into the sewerage system.
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CHAPTER IV
RESULTS AND DISCUSSION.
4.1 Mean and Percentile value of overall samples
The mean and at 90 th and 95 th percentile value of typical composition are
being analysed in this study based on 3 years influent sampling data of raw sewage
taken at headworks of all the Sewage Treatment Plants. The parameters that are
being studied covers the five main sewage characteristics i.e. BOD, SS, COD, AMN
and pH. Other parameters including phosphorous and oil & grease are not included
in this study.
4.1.1 Mean and Percentile for BOD.
From a total number of 29,660 samples sorted and analysed as shown in
Figure 4.1 below, the highest number of samples recorded for BOD concentrations
are within the 151 to 200 mg/l range. By averaging the total number of data, it was
found that the mean value of BOD is 135 mg/l.
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OD
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0
5 1 - 1 0 0
1 5 1 -
2 0 0
2 5 1 -
3 0 0
3 5 1 -
4 0 0
4 5 1 -
5 0 0
5 5 1 -
6 0 0
6 5 1 -
7 0 0
7 5 1 -
8 0 0
BOD Concentration mg/l
N o o f S a m p l e s
Figure 4.1: BOD Concentration range
OD
0
0.2
0.4
0.6
0.8
1
1.2
0 0 - 5
0
5 1 - 1 0 0
1 0 1 -
1 5 0
1 5 1 -
2 0 0
2 0 1 -
2 5 0
2 5 1 -
3 0 0
3 0 1 -
3 5 0
3 5 1 -
4 0 0
4 0 1 -
4 5 0
4 5 1 -
5 0 0
5 0 1 -
5 5 0
5 5 1 -
6 0 0
6 0 1 -
6 5 0
6 5 1 -
7 0 0
7 0 1 -
7 5 0
7 5 1 -
8 0 0 8 0 1 -
BOD Concentration mg/l
% C u m m u l a t i v e F r e q u
e n c
Figure 4.2: BOD Percentile
Further analysis based on the percentage of cumulative frequency versus BOD
concentration range graph in Figure 4.2 above shows that the value of approximately
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220 mg/l and 280 mg/l of BOD at 90% and 95% percentile respectively, which is
within the typical value of 250 mg/l adopted in the local guideline.
4.1.2 Mean and Percentile for COD.
The amount of oxygen needed to oxidize reactive chemicals in water system
as defined by the Chemical Oxygen Demand (COD) is another parameter used to
determine sewage characteristics. The COD chart shown in Figure 4.3 below
indicated that the highest numbers of samples for COD concentration are under the
range of 251 to 300 mg/l. The mean value of COD from a total number of 29,676
samples is 294 mg/l.
It is also observed that the mean characteristic of COD: BOD ratio is approximately
2.3 which roughly shows the organic matter content of the raw domestic wastewater
characteristic.
COD
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0
1 0 1 -
1 5 0
2 5 1 -
3 0 0
4 0 1 -
4 5 0
5 5 1 - 6 0
0
7 0 1 - 7 5
0
8 5 1 - 9 0
0
1 0 0 1
- 1 0 5
0
1 1 5 1
- 1 2 0
0
1 3 0 1
- 1 4 0
0
1 6 0 1
- 1 7 0
0
1 9 0 1
- 2 0 0
0
2 2 0 1
- 2 3 0
0
COD Concentration mg/l
N u m b e r o f S a m p l e s
Figure 4.3: COD Concentration range
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COD
0
0.2
0.4
0.6
0.8
1
1.2
0
1 0 1
- 1 5 0
2 5 1
- 3 0 0
4 0 1
- 4 5 0
5 5 1
- 6 0 0
7 0 1
- 7 5 0
8 5 1
- 9 0 0
1 0 0 1
- 1 0 5
0
1 1 5 1
- 1 2 0
0
1 3 0 1
- 1 4 0
0
1 6 0 1
- 1 7 0
0
1 9 0 1
- 2 0 0
0
2 2 0 1
- 2 3 0
0
COD Concentration mg/l
% C u m m u l a t
i v e
F r e q u e n c y
Figure 4.4: COD Percentile
Based on the graph in Figure 4.4 above, the number of samples analysed depicted
that the value of COD at 90% and 95% percentile are approximately 470 mg/l and
625 mg/l respectively. The 90% percentile value of COD above falls within themedium strength value of 430 mg/l as shown in Table.2.1.
4.1.3 Mean and Percentile for AMN.
The AMN chart in Figure 4.5 below, shows that the highest number of samples for AMN concentration falls under the 16 to 25 mg/l. range. The mean
value of AMN averaging from a total number of 29,674 samples is 23 mg/l.
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AMN
0
1000
2000
3000
4000
5000
6000
0 1-5 6-
10
11-
15
16-
20
21-
25
26-
30
31-
35
36-
40
41-
45
45-
50
51-
55
56-
60
60-
65
65-
70
AMN Concentration mg/l
N u m b e r o f S a m p l e
Figure 4.5: AMN Concentration range
MN
0
0.2
0.4
0.6
0.8
1
1.2
0 1-5 6-10
11-15
16-20
21 -25
26-30
31-35
36-40
41-45
45-50
51 -55
56 -60
60-65
65-70
AMN concentration mg/l
% C u m m u l a t i v e P e r c e n t i l
Figure 4.6: AMN Percentile
In addition, the number of samples analysed in the percentage cumulative format
also shows that the value of AMN at 90% and 95% percentile are approximately 36
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mg/l and 45 mg/l respectively, which fall within the medium and the high strength
category presented in Table 2.1.
4.1.4 Mean and Percentile for SS.
From the SS chart in Figure 4.6 below, it is found that the highest number of
samples for SS concentration fall under the range of 100 to 200 mg/l. The mean
value of SS from a total number of 29,655 samples is 124 mg/l.
SS
0
2000
4000
6000
8000
10000
12000
14000
0
5 1 - 1
0 0
1 5 1 -
2 0 0
2 5 1 -
3 0 0
3 5 1 -
4 0 0
5 0 1 -
6 0 0
7 0 1 -
8 0 0
9 0 1 -
1 0 0 0
1 1 0 1
- 1 2 0
0
1 3 0 1
- 1 4 0
0
> 1 5 0
0
SS concentration mg/l
N u m b e r o f S a m p l e s
Figure 4.7: SS Concentration range
Results from the percentile distribution shown in Figure 4.8 below demonstrate that
the value of SS at 90% and 95% percentile are approximately 200 mg/l and 330 mg/l
respectively. The 95% percentile is within the typical value of 300 mg/l SS adopted
in the local guideline.
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SS
0
0.2
0.4
0.6
0.8
1
1.2
0
5 1 - 1
0 0
1 5 1 -
2 0 0
2 5 1 -
3 0 0
3 5 1 -
4 0 0
5 0 1 -
6 0 0
7 0 1 -
8 0 0
9 0 1
- 1 0 0
0
1 1 0 1
- 1 2 0
0
1 3 0 1
- 1 4 0
0
> 1 5 0
0
SS concentration mg/l
% C u m m u l a t i v e F r e q u e n c
Figure 4.8: SS Percentile
4.1.5 Mean and Percentile for pH
From the pH graph as shown in Figure 4.9 below, the highest number of
samples for pH value falls under the range of 6.7 to 7.4. The mean value of pH from
a total number of 29,374 samples is 6.96.
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Figure 4.9 pH concentration range
H
0
0.2
0.4
0.6
0.8
1
1.2
0 5.9-6.2 6.3-6.6 6.7-7.0 7.1-7.4 7.5-7.8 7.9-8.2 8.3
pH value
% c u m m u l a t i v e p e r c e n t i l e
Figure 4.10: pH Percentile
Likewise, from Figure 4.10 above, the number of samples analysed also shows that
the value of pH at 90% and 95% percentile are approximately 7.2 and 7.4
respectively. All the values for pH either the mean or the 90% and 95% percentile,
H
0
2000
4000
6000
8000
10000
12000
0 5.9 -6.2 6.3-6.6 6.7-7.0 7.1-7.4 7.5-7.8 7.9 -8.2 8.3
pH value
% c u m m u l a t i v e p e r c e n t i l e
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are considered within the optimum value that is conducive for bacterial growth
which lies between 6.5 and 7.5 levels as suggested in Metcalf and Eddy (2004).
Table 4.1: Characteristics of domestic wastewater from all samples.
Concentration
Contamin
antsUnit
Number
of
Sample
s
Mean
90th
Percen
tile
95th
Percen
tile
UTM-
IWK
Study
(mean)
Metcalf
& Eddy
(medium
strength)
BOD mg/L 29,660 135 220 280 239 190
COD mg/L 29,676 294 470 625 420 430AMN mg/L 29,674 23 36 45 28 25
SS mg/L 29,655 124 200 330 103 210
pH - 29,374 6.96 7.2 7.7 - 6.5-7.5
Table 4.1 shown above summarised the value of all the five parameter analysed
from the entire data made available in the study. The result illustrates that the 90th
percentile values in the analysis are the values comparable with the results from both
the UTM-IWK collaborative study (2003) and the value outlined in Metcalf & Eddy
(2004).
4.2 Mean sewage characteristics based on type of Developments.
In domestic wastewater, the composition of sewage varies from location to
location. It also varies with the time of day or season (weekday, weekend, holidays,
and climatic condition) and fluctuates even at the same location due to changes of
activities. Domestic wastes are mostly originated from showers, toilets, washing of
dishes and clothes, and from the kitchen. It is also important to note that not all of
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the residential units are fully discharging domestic wastewater loads to the sewer
system. There are many instances in which the outflow from kitchen sinks and
washing machines are directly discharged to the perimeter drainage system mostly
located at the back of residential units.
In addition, the domestic wastewater load is also affected by the type of the
development it originated. Townships are today encouraging industrial parks and
commercial complexes to spur economic growth for the area. Commercial premises
include assembly halls, camps, clubs, hotels, institutions, offices, restaurants,
schools, stores, laundry, swimming pool, theater, rest and service areas, bus station,
wholesale, retail, finance, auto repair, amusement centres, clinic, museum and
airport etc. Whilst, industrial establishment include factories that manufacture food,
textile, paper, printing, chemical, plastic and electronic product etc. Although the
sewer system provided for these areas are designed to cater for domestic wastewater
(the trade wastewater are to be treated separately), it is an almost impossible task to
control the wastewater from entering the sewage especially via spillage, inflow from
washing activities or illegally discharged into the sewer connection. All these has
bearing to the sewage characteristics transported into the treatment system .
A typical example is wastewater generated from verhicle services centre that include
spills in the form of lubrication oil, engine coolant, traces of petrol and diesel,
solvent from paintworks, cleaning agent and eletrolyte from batteries. Since source
control at service centres are not enforced, the result is considered ineffective due to
lack of enviromental awareness amongst the workshop operators. Hence, what is
needed is effective enforcement efforts that help to contain illegal trade waste
discharge.
This scope of the study is an attempt to identify the typical difference in the
characteristics of raw sewage generated from various types of developments in the
country i.e. from residential, commercial, industrial and also mixed developments.
The raw sewage data are divided into seven different types of development
categories that have been identified as: (i) residential only (ii) commercial only (iii)
industrial and commercial institutions (iv) developments with industrial plots (v)developments with commercial plot (vi) Industrial and industrial plus commercial
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and (vii) residential and commercial developments. Samples were sorted and
analysed based on the above category of developments. A summary of the mean
value of sewage characteristics is as in Table.4.2 below.
Table 4.2: Mean domestic wastewater characteristics based on type of
Developments.
Types of Development BOD COD AMN pH SS No of
Samples
Commercial only 227 482 19 6.9 212 401
Commercial and
Industrial 210 43523 6.8 170
106
Industrial and
Commercial plus
Industrial
174 365 21 6.8 147 134
Mixed development with
commercial plots* 134 295 20 6.9 144 5866
Residential only 130 290 20 7.0 140 9575
Residential and
Commercial 127 281 20 6.9 139 5453
Mixed development with
Industrial plots** 121 262 17 6.7 130 352
Note: The influent from fully Industrial plots are not being analysed as
the sampling data are very minimal from only 3 areas with full
industrial premises.
* Development with commercial only and commercial plus residential.
**Development with industrial only, industrial plus commercial, industrial
plus residential and industrial plus commercial plus residential.
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Based on the results as show in Table 4.2 above and Figure 4.11 below, all the three
BOD, COD and SS parameters were found higher from source that originated from
development with commercial plots, medium from residential premises and thelowest from mixed development with industrial plots.
All the three parameters i.e. for BOD are descending from 227 mg/l to 121 mg/l ,
COD from 482 mg/l to 262 mg/l and SS from 212 mg/l to 130 mg/l.
As for parameter for AMN, the level was found lower from mixed development with
industrial plot areas and higher from commercial plus industrial premises. The AMNvalues ranged from 17mg/l to 23 mg/l.
Dev.type
0
100
200
300
400
500
600
Commercialonly
Commercialand Industrial
Industrial andCommercial
plusIndustrial
Developmentwith
commercial plots*
Residentialonly
Residentialand
Commercial
Developmentwith
Industrial plots**
Type of Developments.
C h a r a c t e r i s t i c m g / l ( e x p H )
BOD
COD
AMN
PH
SS
Figure 4.11: Mean domestic wastewater characteristic from different
type of Developments.
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Mean levels of pH concentrations are within the range of 6.7 to 7.0 indicating that
the results are within the tolerable value.
All the values identified in Section 4.2 differ slightly from the results gathered and
anlysed in Section 4.1. The finding in Section 4.1 dealt with influent data collected
from more than 4,200 STP for overall analysis. In comparison, the analysis in
Section 4.2 are based on a lower number of samplings linked to customers database,
from roughly 1,400 sewage treatment systems of which the types of connected
premises of the development have been duly verified.
4.3 Domestic wastewater characteristics based on size of Developments.
The study in this section will identify the typical raw sewage characteristics
measured in relation to the size of developments which are normally linked to the
length of sewer reticulation, area of coverage, in-pipe storage, duration of flow and
infiltration. The determination in the size of development in this analysis is based on
the connected PE to the Sewage Treatment Plant.
Wastewater collection system conveys wastewater from its sources to locations
where it may be treated and ultimately discharged to a receiving water body.
Wastewater collection systems are laid in such a pattern with smaller sewers flowing
into larger sewers. Although it is designed to collect and transport wastewater from
human sanitary activities, nevertheless unintended or illegal connection frequently
resulted in the entry of additional flow into the system. Infiltration is water that
enters the system from the ground through defective pipes, pipes joints, lateral
connection or from manhole walls.
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Table 4.3 Size of Developments – Mean domestic wastewater characteristic
PE Range BOD COD AMN pH SSNo of
Samples
< 1000 164 393 25 7.1 202 11,266
1,001 - 2,000 152 342 23 7.1 165 4,645
2,001 - 3,000 153 338 23 7.1 156 4,052
3,001 - 5,000 147 316 22 7.1 141 3,624
5,001 - 10,000 141 313 22 7.0 137 3,267
10,001 -20,000 140 308 22 7.0 140 2,057
20,001 - 50,000 122 279 20 6.9 139 898
50,001 - 100,000 126 285 22 7.1 138 233
>100,001 119 261 18 6.9 147 268
Table 4.3 above and Figure 4.12 below illustrated the relationship between sizes of
development and human populations with concentration of the wastewater
constituents. Based on the analysis as tabulated above, the sewage characteristics
from the various development shows a peculiar and distinctive pattern thatcorrespond to the changes in size of the development. Seemingly, the sewage
concentration is indicating a significantly lower value from the large developments
and the parameters incrementally higher from those that originated from smaller
development.
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Depending on the length of sewer networks, the flow generated from the source may
require several hours to flow through the sewer network system because of flow
dampening effect and prolonged by the available storage capacity in the sewer
system.
The findings generated from the above scenario prompted this study to further look
at the impact of the decreasing pattern associated with the changes in size of the
development. Pursuant to this, all the parameters analysed earlier are now plotted
individually to observe its significance. It is necessary to be aware that the current
sewerage guideline which stipulates that development with more than 30 units
(150PE) shall be served by a connected sewerage system and a treatment plant.
Likewise, a sewerage asset record shows that only two percent of the developments
in the country are served by STPs with more than 100,000 PE. In the following
analysis, all development less than 150PE and 150,000PE and above are omitted and
consideration is made to observe only developments between the 150PE to 150,000
PE range.
BOD
y = -0.0003x + 135.93
0
100
200
300
400
500
600
700
800
0 20000 40000 60000 80000 100000 120000 140000
Size of Development
B O D C o n c e n t r a t i o n m g /
Figure 4.13: BOD variation with increase in development size .
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The BOD analysis involved a total number of 29,070 sampling data. Comparison
done to BOD concentration levels in the graph in Figure 4.13 shows that for
development with 150 PE indicates BOD mean value of 135 mg/l and the value
decreases to 106mg/l. for development with more than100,000 PE. This is
equivalent to a reduction of approximately 20% in the value of BOD concentration
between this two development ranges.
COD
y = -0.0007x + 300.45
0
500
1000
1500
2000
2500
0 20000 40000 60000 80000 100000 120000 140000
Size of Development
C O D C o n c e n t r a t i o n m g /
Figure 4.14: COD variation with increase in development size .
The COD analysis involved a total number of 29,173 sampling data. Again
comparison is made to the COD concentration levels as shown in Figure 4.14 which
illustrated that for development with 150 PE indicates the a COD value of 300 mg/l
and the value decreases to 230mg/l for development with more than 100,000 PE.
This is equivalent to a reduction of approximately 23% in the value of COD
concentration between this two development ranges.
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AMN
y = -6E-05x + 23.35
0
10
20
30
40
50
6070
80
0 20000 40000 60000 80000 100000 120000 140000
Size of Development
A M N c o n c e n t r a t i o n m g /
Figure 4.15: AMN variation with increase in development size .
The AMN analysis involved a total number of 29,191sampling data. As for
Ammonia Nitrogen concentrations, the analysis in Figure 4.15 shows that for
development with 150 PE indicates the AMN mean value of 23 mg/l and the value
decreases to 17mg/l for development with more than 100, 000 PE. This is equivalent
to a reduction of approximately 25% in the value of AMN concentration between
this two development ranges.
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SS
y = -0.0002x + 125.65
0
200
400
600
800
1000
12001400
1600
1800
0 20000 40000 60000 80000 100000 120000 140000
Size of Developments
S S c o n c e n t r a t i o n m
g /
Figure 4.16: SS variation with increase in development size .
The SS analysis involved a total number of 29,176 sampling data. The SS
concentration level in the graph in Figure 4.16 shows that for development with 150
PE indicates the SS mean value of 126 mg/l and the value decreases to 106mg/l for
development with more than 100,000 PE. This is equivalent to a reduction of
approximately 16% in the value of SS concentration between this two development
ranges.
pH
y = -1E-06x + 7.0525
0
1
2
3
4
56
7
8
9
0 20000 40000 60000 80000 100000 120000 140000
Size of Development
p h v a l u e
4.17: pH variation with increase in development size
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43
Meanwhile, analysis of pH in relation to different development size involved a total
number of 29,165 sampling data. Figure 4.17 shows the pH level for development
with 150 PE indicates the mean value of 7.0 and the value decreases to 6.9 for
development with more than 100,000 PE. This is equivalent to a reduction of
approximately 1.4% in the value of pH concentration between this two development
ranges.
Results from analyses for all the 5 parameters as depicted in the above
charts, revealed that the domestic wastewater characteristics generated from
100,000PE developments are lower in strength (by 20% for BOD, 23% for COD,
25% for AMN, 16% for suspended solids and 1.4% for pH) compared with
characteristics of wastewater originated from 150 PE developments.
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44
CHAPTER V
CONCLUSIONS
5.1 Wastewater characteristics based on the overall analysis
The characteristics of influent wastewater are different depending on
numerous factors, including variations in the size and type of developments, the
extent and nature of industrial and commercial premises in the catchment area,
community composition and the seasonal variability of sewage entering the
treatment facility. The magnitude of its material composition is a function of
environmental variables in the wastewater generated from source including the
length of sewer network, volume of storage, pipe gradient, oxygen content in the
sewer system, ethnic and religious norms in water usage, type and composition of
the establishments in the service areas. The characteristics of influent wastewater
identified in this study are as follows:
i) The mean and at 90 th and 95 th percentile values for all samples of raw
domestic wastewater based on five main sewage characteristics i.e. BOD, SS,
COD, AMN and pH are as shown in Table 5.1.
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Table 5.1: Characteristics of domestic wastewater from all samples.
Concentration
Contaminants UnitMean
90th
Percentile
95th
PercentileBOD mg/L 135 220 280
COD mg/L 294 470 625
AMN mg/L 23 36 45
SS mg/L 124 200 330
pH - 6.96 7.2 7.7
ii) For analysis based on different type of developments, three parameters for
BOD, COD and SS were found to be higher from sources originated from
commercial plots, medium in strength from residential premises and lower in
strength from industrial developments. The value of BOD descended from
227 mg/l to 121 mg/l, COD from 482 mg/l to 262 mg/l and SS from 212
mg/l to 130 mg/l. The characteristic for AMN was found to be lower from
mixed developments with industrial plots areas and higher from industrialwith commercial premises with values ranging from 17 mg/l to 23 mg/l.
Mean levels of pH concentrations are within the tolerable value of 6.7 to 7.0.
iii) Domestic wastewater also shows patterns that correspond to the changes in
size of the developments. The domestic wastewater concentration indicated a
lower value from large developments and the characteristics are
incrementally higher from those that originated from smaller developments.Large developments with high PE normally have wider area of coverage and
longer sewer piping system. This clearly consolidated the findings by other
research studies regarding the influence of in-pipe treatment in the sewerage
conveyance system.
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5.2 Recommendations
Due to a wide variation of sewerage characteristic recorded, it is proposed that the
parameter to be adopted for the design of a new plant built by the industry shall be
based on the value within the range of 90% and 95% percentile, which are
equivalent to the current typical value for BOD and SS. However, for treatment
works financed by the Government of which the capital investment is drawn from
public funds, the characteristics of sewage adopted in the design shall be based on
lower values (mean or median) to optimize the design and in ensuring for priority
and the economic viability of Government projects.
In order to identify the factors associated with the changes of wastewater
characteristics affected by the difference in size of developments, it is recommended
that a further study be carried out to identify the coefficient or factor to be adopted
as multiplier to wastewater characteristic in proportion to the increase in the size of
development. Similarly, a further study is also needed to be initiated to identify the
basis for the variation of wastewater characteristic significantly affected by a
particular type of trade activities involved and also due to the differences in
composition/ percentage of industrial and commercial premises in the study area.
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APPENDIX A
Table A1: Cumulative frequency of BOD range
BOD range
Number of
samples Percentage
Cumulative
percentage.
0-50 4489 15.13% 15.13%
51-100 6765 22.81% 37.94%
101-150 7842 26.44% 64.38%
151-200 5809 19.59% 83.96%
201-250 2369 7.99% 91.95%
251-300 986 3.32% 95.27%
301-350 551 1.86% 97.13%
351-400 236 0.80% 97.93%
401-450 155 0.52% 98.45%
451-500 115 0.39% 98.84%
501-550 85 0.29% 99.13%
551-600 66 0.22% 99.35%
601-650 65 0.22% 99.57%
651-700 49 0.17% 99.73%
701-750 32 0.11% 99.84%
751-800 31 0.10% 99.94%
>801 15 0.05% 100.00%
29660 100.00%
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APPENDIX B
Table B1: Cumulative frequency of COD range
COD range
Number of
samples Percentage
Cumulative
percentage.
0-50 1357 4.57% 4.57%
51-100 2316 7.80% 12.37%
101-150 2763 9.31% 21.68%
151-200 3619 12.20% 33.88%
201-250 3936 13.26% 47.14%
251-300 4237 14.28% 61.42%
301-350 3583 12.07% 73.49%
351-400 2671 9.00% 82.49%
401-450 1586 5.34% 87.84%
451-500 852 2.87% 90.71%
501-550 484 1.63% 92.34%
551-600 414 1.40% 93.74%
601-650 281 0.95% 94.68%
651-700 265 0.89% 95.58%
701-750 196 0.66% 96.24%
751-800 176 0.59% 96.83%
801-850 123 0.41% 97.24%
851-900 93 0.31% 97.56%
901-950 72 0.24% 97.80%
951-1000 53 0.18% 97.98%
1001-1050 62 0.21% 98.19%
1051-1100 39 0.13% 98.32%
1101-1150 46 0.16% 98.47%
1151-1200 42 0.14% 98.62%
1201-1250 31 0.10% 98.72%
1251-1300 26 0.09% 98.81%
1301-1400 54 0.18% 98.99%
1401-1500 40 0.13% 99.12%
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1501-1600 57 0.19% 99.32%
1601-1700 42 0.14% 99.46%
1701-1800 29 0.10% 99.56%
1801-1900 34 0.11% 99.67%1901-2000 37 0.12% 99.80%
2001-2100 22 0.07% 99.87%
2101-2200 20 0.07% 99.94%
>2201 18 0.06% 100.00%
29676 100.00%
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APPENDIX C
Table C1: Cumulative frequency of AMN range
AMN range
Number of
samples Percentage
Cumulative
percentage.
0 0 0 0
1-5 1419 4.78% 4.78%
6-10 2393 8.06% 12.85%
11-15 4108 13.84% 26.69%
16-20 5517 18.59% 45.28%
21-25 5184 17.47% 62.75%
26-30 4229