ADVANTAGES AND DISADVANTAGES OF MICROPOROUS FOR …

ADVANTAGES AND DISADVANTAGES OF MICROPOROUS

MEMBRANES IN A HOLLOW FIBER BIOREACTOR

FOR SPACE APPLICATIONS

by

MARIA NOEL RUIZ CARERI, B.S.Ch.E.

A THESIS

IN

CIVIL ENGINEERING

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

IN

CIVIL ENGINEERING

Approved

Audra Morse Chairperson of the Committee

Andrew Jackson

Accepted

John Borrelli Dean of the Graduate School

August, 2005

ii

ACKNOWLEDGMENTS

I would first like to thank my major advisor, Dr. Audra Morse, who guided me

through my graduate studies at Texas Tech University. I appreciate her constant support,

patience, and understanding during my thesis writing and all the help she provided me to

complete my degree. Also, my appreciation goes to Dr. Jackson, for participating on my

committee, for his review of this thesis, and also for giving me the opportunity to obtain a

remarkable work graduate experience.

Thanks to the Texas Tech Athletic Department, without them I would never have

had the opportunity to be in this country. I am very grateful to my co-workers and

friends who have been with me in the last couple of years, and without the TTU-NASA

research team this research would not have been possible. Thanks to Dr. Dallas and the

people in electrical engineering for taking their time to help me out, to Dr. Heyward

Ramsey for his encouragement and trust in the past couple of years, and to Eric

McLamore, for his patience and understanding on those crazy days where nothing made

sense, for always giving me a good laugh.

And of course, special thanks go to my family, especially my parents, who have

always been there to support me and taught me to never quit. Also, to my sister who

gave me the confidence to finish my degree and succeed in anything I do. They have

played the most important role in forming the person I am today.

iii

TABLE OF CONTENTS

ACKNOWLEDGMENTS ii

ABSTRACT vii

LIST OF TABLES viii

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiii

CHAPTER

I. INTRODUCTION 1

II. BACKGROUND 5

2.1Water in Space 5

2.2 Hollow Fiber Membrane Bioreactors 6

2.2.1 Membrane Types and Geometry 7

2.2.2 Membrane Modes for Aeration 9

2.3 Nitrification 10

2.4 Transport Processes 14

2.4.1 Hydrodynamics 16

2.4.2 Mass Transfer 16

2.4.3 Dimensionless Groups 19

2.5 Biofilms 20

2.5.1 Biofilm Development 21

2.5.2 Biofilm in MABRs 21

iv

III. MATERIALS AND METHODS 23

3.1 Membrane Module 23

3.2 HFMBR 25

3.2.1 Inoculation 25

3.2.2 Feed Composition 26

3.3 HFMBR Reactor System 27

3.3.1 System Components 27

3.3.1.1 Pressure Measurement 27

3.3.1.2 Connections 27

3.3.2 Analytical Methods 29

3.4 Loading Studies 29


3.6 Hydrodynamics/Tracer Studies 31

3.7 Mass Transfer Experiments 32

3.8 Biofilm Analysis 33

3.8.1 Determination of biofilm distribution throughout the bioreactor 35

3.8.1.1 Circumferential Analysis 35

3.8.1.2 Longitudinal Analysis 35

3.8.1.3 Outside-in Strategy 36

3.8.2 Identification of the bacteria present within the biofilm 37

v

3.8.2.1 Identification of heterotrophic bacteria by cultivation in nutrient

agar 38

3.8.2.2 Identification of Nitrobacter species by AT5N Medium 38

3.8.2.3 Identification of Nitrosomonas Europaea by AT5N Medium 39

IV. RESULTS 41


4.2 Loading Studies 48

4.3 Hydrodynamics 55

4.4 Mass Transfer 61

4.5 Biofilm Analysis 70

4.5.1 Visual Analysis 71

4.5.2 Circumferential Analysis 75

4.5.3 Longitudinal Analysis 76

4.5.4 Biofilm Thickness 77

4.5.5 Bacteria Identification 82

V. CONCLUSIONS 84

REFERENCES 88

APPENDICES

A. RAW DATA DURING THE HFMBR STUDY 94

B. RAW DATA. SIGMA PLOT GRAPHS 114

C. MASS TRANSFER CALCULATIONS 118

vi

D. TRACER STUDY CALCULATIONS 128

E. T-TEST 135

vii

ABSTRACT

Texas Tech University (TTU) works in conjunction with NASA to develop a

wastewater recovery system robust enough for use on long term-space missions.

Biological treatment has been the primary focus at TTU, with specific thrusts in

developing a biological treatment system that may be operated with minimal crew

maintenance and low energy and mass requirements.

Hollow fiber membrane bioreactors (HFMBRs) may be used for biological

wastewater treatment, and may be integrated with NASA’s current research

developments. The goal of this research is to (a) evaluate the effect of mass transfer by

the use of microporous membranes and their application for microgravity conditions; (b)

compare the effect of membrane type and configuration on treatment efficiency to

previous literature values; and (c) determine the amount and distribution of biofilm

growth within the reactor. Therefore, the objective of this research was accomplished

using a microporous HFMBR.

From the experimental studies performed for this thesis it was found that the

HFMBR exhibits promising use in space applications. Maximum nitrification efficiency

at low loading rates and high HRTs were accomplished using the HFMBR. Therefore,

characteristics such as, suitable bioreactor size and the efficiency obtained during its

operation, the HFMBR offer a potential for NASA’s needs; nonetheless, developing a

system with more favorable system hydrodynamics would aid to improve treatment

efficiency in a HFMBR

viii

LIST OF TABLES

2.1 Dimensionless numbers 20

3.1 HFMBR Characteristics 25

3.2 Composition of HFMBR feed 26

3.3 Nutrient agar composition 38

3.4 AT5N medium composition (Nitrobacter) 39

3.5 AT5N Medium Composition (Nitrosomonas) 40

4.1 Evolution of nitrification process 43

4.2 Effluent results for HFMBR during +4NH -N loading 44

4.3 Ammonium-nitrogen removal rate from various treatment systems 47

4.4 Mass removed at a constant rate 54

4.5 Dispersion in the HFMBR 59

4.6 HFMBR mass transfer without biofilm 62

4.7 Oxygen transfer within the HFMBR 63

4.8 HFMBR mass transfer after biofilm formation 65

4.9 Dimmensionless numbers 67

4.10 Comparison of mass transfer correlations from literature 70

4.11 Cross-sectional mass per surface area 75

4.12 Longitudinal mass per surface area 77

4.13 Biofilm thickness 78

A1 Test point 1. Influent Concentrations (mg/L) 95

ix

A2 Test point 1. Effluent Concentrations (mg/L) 96













A15 Average Values 109

A16 Standard Deviation Values 110

A17 Volumetric Conversion Rates 111

A18 Mass Calculations 112

A19 Reactor Efficiency using variable surface areas 112

A20 Sample Calculations 113

C1 Initial DO calculations at 0.3 mL/min 119

C2 Initial DO calculations at 5 mL/min 120


x


C5 Initial DO calculations. Summary table 123

C6 Final DO calculations at 0.3 mL/min 124

C7 Final DO calculations at 1 mL/min 125

C8 Final DO calculations at 10 mL/min 126

C9 Final DO calculations. Summary table 127

C10 Biofilm consumption 127

D1 Initial tracer at 0.3 mL/min 129

D2 Initial tracer at 1 mL/min 130

D3 Initial tracer at 15 mL/min 131

D4 Final tracer at 0.3 mL/min 132

D5 Final tracer at 1 mL/min 133

D6 Final tracer at 15 mL/min 134

xi

LIST OF FIGURES

2.1 Mass Transfer in a nitrifying microporous HFMBR 17 3.1 Hollow fiber membrane reactor (HFMBR) schematic 24

3.2 Hollow fiber membrane reactor system layout 28

3.3 HFMBR module 28

3.4 Sampling locations within the HFMBR 34

3.5 Different cross-sections within the HFMBR 36

3.6 Membrane sampling 37

4.1 HFMBR conversion rates 42

4.2 HFMBR efficiency 45

4.3 Volumetric conversion rates 49

4.4 Conversion rates per surface area 50

4.5 Overall reactor performance 51

4.6 Conversion rate comparison 53

4.7 Comparison of the HFMBR removal efficiencies 55

4.8 Hydrodynamic experiments without biofilm 57

4.9 Hydrodynamic experiments after biofilm growth 58

4.10 Oxygen transfer within the HFMBR 64

4.11 Sherwood vs. Reynolds number. Before and after biofilm formation 69

4.12 Sampling locations within the HFMBR 71

4.13 Biofilm growth within different locations of the HFMBR 73

xii

4.14 Outside-in strategy 74

4.15 Biofilm distribution within the HFMBR 76

4.16 Biofilm thickness 78

4.17 Biofilm thickness at sections 2A and 3A 80

4.18 Biofilm thickness at sections 4A and 5A 81

B1 Raw data for pH and TDS 115 B2 Raw data for dissolved oxygen and ammonia 116 B3 Raw data for nitrogen oxides 117

xiii

LIST OF ABBREVIATIONS

d Unitless dispersion number

D Diffusion coefficient

DDI Deionized, distilled water

DO Dissolved oxygen

HFMBR Hollow fiber membrane bioreactor

HRT Hydraulic retention time

J Flux

JE Experimental flux

JM Flux consumed by microorganisms

KL Mass transfer coefficient in the liquid phase

KO Overall mass transfer coefficient

MABR Membrane aerated bioreactor

+4NH -N Ammonium

−2NO -N Nitrite

−3NO -N Nitrate

−xNO -N Nitrogen oxide

Pe Peclet number

Re Reynolds number

Sc Schmidt number

Sh Sherwood number

1

CHAPTER I

INTRODUCTION

From the early 1970s to about 1980, the primary worries for wastewater treatment

were aesthetic and environmental concerns as indicated by the reduction of biological

oxygen demand, total suspended solids, and pathogenic organisms (Metcalf & Eddy,

2003). Later, the removal of nutrients began to be addressed. As time passed, the goals,

and objectives became, and still are, more strictly related to the water quality.

Wastewater treatment methods involve physical, chemical, or biological

reactions. However, wastewater treatment is not only applied in terrestrial environments,

but also wastewater treatment is a concern in space. Long duration space missions will

require the reuse of water supplies.

NASA is currently evaluating different physical and chemical methods for the

recovery of wastewater. A Water Recovery System (WRS) is necessary for long-term

space missions due to the limited capacity for water storage due to weight and volume

requirements. It is definitely a challenge for the WRS to produce stable and healthy

water from a wastewater stream composed of gray-water (hand, body, clothes, and dish

washing), humidity condensate, and urine. Biological wastewater treatment methods, as

well as the physical and chemical methods, also provide the possibility of organic carbon

removal, as well as ammonia and nitrate from wastewater. Biological wastewater

methods have the advantage of low energy requirements, no additional chemical

requirements for the treatment process, and the production of less waste material

2

requiring storage and handling. Therefore, biological treatment is a cost-effective

method for the replacement of the physical and chemical techniques currently considered

in space.

NASA’s Johnson Space Center (JSC) and Texas Tech University (TTU) have

been working simultaneously with the purpose of developing a robust system to be

operated under microgravity conditions and cost effective enough to be used for long-

term missions. Texas Tech University (TTU) currently operates several biological

systems for wastewater treatment (Morse et al., 2003; Jackson et al., 2004; Muirhead, et

al., 2003; and McLamore, 2004) including: the TTU-WRS, two membrane aerated

bioreactors, referred to as MABRs, a commercial hollow fiber polypropylene

microporous membrane bioreactor (HFMBR), and a dual system that promotes

simultaneous nitrification and denitrification (sAMR). In the TTU-WRS system,

nitrification is promoted in a tubular reactor located downstream of a packed bed reactor,

in which denitrification occurs. Nitrification refers to the conversion of ammonium to

nitrite and nitrate under aerobic conditions, while denitrification is the conversion of

nitrite and nitrate into nitrogen gas under anaerobic conditions (Jackson et al., 2004; and

McLamore et al., 2004). This system presented several maintenance and performance

problems; therefore, the design and treatment efficiency of a membrane-aerated

bioreactor to treat NASA's simulated wastewater was considered.

MABRs are hollow fiber membrane reactors that consist of permeable tubes

through which oxygen is diffused into the system in order to support biofilm growth.

MABRs present several advantages over the tubular reactor such as bubble-free aeration,

3

low solids production, high resistance to shock loadings, and low maintenance (Morse et

al., 2003). However, effective membrane type and configuration has not been

established. For example, membranes may be placed in parallel or randomly distributed

within the reactor. Parallel membranes refer to a straight configuration where the

membranes do not come in contact with each other, while on the other hand, random

membranes refer to the arbitrarily distribution of the membranes in the reactor.

Research at TTU focuses on the use of silicone membranes randomly distributed

within MABRs. The selection of random membranes over parallel membranes was due

to the assumption that by using random membranes mixing would be enhanced;

therefore, increasing transport and improving overall reactor performance. However, the

most effective membrane type and configuration has not been established. Results show

that random membranes could increase transport but certain difficulties may be faced due

to the application of this type of packing configuration, presenting a drawback to their

application. Bao and Lipscomb (2002) analyzed the effect of packing configuration on

mass transfer, and results indicated reduction in mass transfer due to channeling

(formation of biofilm) in randomly distributed fibers. Also, the use of microporous

membranes could contribute to a more efficient treatment; however, their use could

present a problem when applied under microgravity conditions. Silicone membranes can

be operated at higher pressures without forming bubbles, while the formation of bubbles

is possible in microporous membranes due to the porosity of the membranes (Ahmed and

Semmens, 1992).

4

Hollow fiber membrane bioreactors are most commonly used for filtration

purposes. Membranes have been used to remove contaminants from wastewater in

microfiltration and ultrafiltration. For systems previously used, hollow fiber membranes

have also been used for gas stripping. By applying a vacuum through the membranes,

volatile organic compounds have been removed from wastewater streams. However, the

use of HFMBRs for stripping does not present the same problems as when used for

aeration purposes. Some of the anticipated problems presented when using HFMBRs for

aeration purposes are short circuiting as a result of biofilm growth in between the

membranes and the lack of flow control since the use of a vacuum is not applied.

Although some difficulties will arise, it is believed that the use of microporous

membranes, in comparison to silicone membranes, would increase transport of oxygen

through the membranes, improving the treatment efficiency within HFMBRs. Therefore,

the HFMBR is a possible candidate for the replacement of the tubular reactor. However,

all previous studies performed on HFMBRs have been with silicone and randomly

distributed membranes.

Thus there is a need to evaluate the effect of membrane type and configuration in

overall treatment efficiency of the reactor. The objectives of this thesis are to analyze the

advantages and disadvantages of microporous membranes in a hollow fiber membrane

bioreactor by (a) evaluating the effect of mass transfer by the use of microporous

membranes and their application for microgravity conditions; (b) comparing the effect of

membrane type and configuration on treatment efficiency to previous literature values;

and (c) determining the amount and distribution of biofilm growth within the reactor.

5

CHAPTER II

BACKGROUND

2.1 Water in Space

By the advance of science, humans have been able to explore space. Today, long-

term missions are not self sufficient. In long-term space missions, such as a trip to Mars,

astronauts need to perform the same activities in a space shuttle, without gravity, and

reduced space, but they still need to eat and drink. Therefore, the National Aeronautics

and Space Administration (NASA) has been working to develop a wastewater treatment

system for potential use in space applications.

Water is one of the most crucial provisions astronauts need to live and work in

space. That is why NASA has been working in developing physical, chemical or

biological methods to be applied to recycle the wastewater with the ultimate goal of

reducing the cost of missions by decreasing the payload weight. NASA’s focus in the

past had been physical and chemical systems to recycle water. However, NASA is

concentrating in developing biological processes for space applications.

NASA’s first four manned spaceflight projects were Mercury, Gemini, Apollo,

and SkyLab. In the past, water was generated by fuel cells that were used to provide

energy for the spacecraft and potable water was generated as a by-product, and water has

been recycled by physicochemical processes. A Water Recovery System (WRS) needs to

be 100% efficient, self-sufficient and capable of operation in microgravity conditions.

The use of a biological process for space applications may be energy efficient and

6

self-sufficient, require little or no maintenance in order to minimize the crew’s time for

other tasks, require little to no chemicals, and have low mass.

There are two main goals to be accomplished when operating a biological system;

the removal of organic constituents as well as the removal of nitrogen compounds. The

earliest version of a biological WRS was an immobilized cell bioreactor, conducted at

Johnson Space Center (JSC) in 1997 (Pickering et al., 1997). Also, other systems have

been previously analyzed (Finger et al., 1999; Petersen et al., 1991) that included

membrane technologies to develop membrane bioreactors. It is important to remember

that biological processes are followed by physiochemical to complete the water recycling

process, but they are not discussed in this thesis. The scope of this thesis is to evaluate a

membrane bioreactor for its application in space.

2.2 Hollow Fiber Membrane Bioreactors

The use of membranes for treatment of water and wastewater has increased in the

last several years. Membrane aerated bioreactors are hollow fiber membrane bioreactors

(HFMBRs), used most commonly for filtration, that represent a new technology for

aerobic wastewater treatment. Advantages such as bubble free aeration, low solids

production, high resistance to shock loadings, high nitrification efficiency, low

maintenance and a decrease in space requirements can be achieved by the use of

HFMBRs. In a hollow fiber bioreactor, oxygen flows through the lumen side of the

hollow fibers and oxygen diffuses through the wall of the membrane. Oxygen is utilized

by the bacterial population attached to the surface of the membranes, creating a driving

7

force for mass transfer. The membranes provide high oxygen permeability, ensuring the

transport of oxygen through the membranes and providing surface area for biofilm

attachment and treatment to occur.

The most important benefit obtained from HFMBRs is higher mass transfer.

Casey et al. (1999), establishes that the main advantage in process performance between

HFMBRs and conventional reactors is the active layer of biofilm formed on the

membranes and the importance of the active layer location. Depending on the waste

stream, most HFMBRs, consist of aerobic nitrifying bacteria located on the outside of the

film close to the membrane walls where oxygen is being provided and the anaerobic

denitrifying bacteria is located on the inside of the film where there is high organic

matter; therefore, dual mass transfer of oxygen and nutrients occurs from the inside and

outside of the membranes.

2.2.1 Membrane Types and Geometry

Membrane types and geometry are some important features to consider in order to

develop a low mass and energy efficient biological system. Selection of an appropriate

membrane is perhaps the most important feature. Membranes made of teflon, silicone,

gore-tex, polyetherimide, and silicone with fibrous support, silicone and polypropylene

have been used in the past for the removal of different pollutants such as synthetic

sewage, food processing wastewater, organic carbon and inorganic nitrogen between

others (Torrey, 1984). The configurations of membranes used include tubular, plate and

frame, single tube, tubular coil, and hollow fiber (Casey et al., 1999).

8

Aeration within a reactor is achieved by the use of membranes. Pressure provides

a gradient to encourage aeration through the membranes. The pressure driven

membranes are divided into three divisions based on membrane surface. These

membranes can be microporous, dense (silicone), and composite (dense coats on

microporous membranes). Membrane characteristics such as mass transfer, permeability,

pressure limitations, and membrane life span are some factors to take in consideration.

Microporous membranes present the advantage of having negligible resistance to

mass transfer; the bubble free form of aeration results in near 100 percent mass transfer

(Grimberg et al., 2000). Mass transfer takes place by diffusion through the pores of the

membrane. Nonetheless, pressure regulations are restricted due to the formation of

bubbles. The disadvantage of microporous membranes is the limitation to operating

pressure for which a pressure difference across the membrane of 2 to 3 psi was found to

cause bubbles (Ahmed and Semmens, 1991). If liquid penetrates into the micropores of

the membranes, reduction of mass transfer is observed and bubbles can be produced. The

formation of bubbles may present a drawback for the application of this type of

membranes under zero-gravity conditions. The life span of this type of membrane is

reduced due to the deposition of suspended solids and oils within the pores (Casey et al.,

1999) and they cannot be found in small diameter, and are relatively expensive.

Recent studies have investigated the replacement of porous membranes with

silicone membranes for wastewater applications (Ahmed and Semmens, 1992; Brindle

and Stephenson, 1996). Transport in dense membranes occurs via diffusion due to a

pressure differential. Oxygen has a high solubility in silicone; therefore, most dense

9

membranes are made of silicone. Dense membranes present several advantages over

microporous membranes, such as the use of high intramembrane oxygen pressures (up to

3*105 Pa) (Casey et al., 1999), high resistance to chemical and mechanical stress due to

the absence of pores, and the reduction of membrane fouling. In comparison to

microporous membranes (only when bubbles are formed), silicone membranes can also

operate at higher pressures without bubble formation, generating higher mass transfer

rates. Overall, dense membranes have better oxygen mass transfer with membrane

aeration than bubble aeration and have higher life span than microporous membranes.

2.2.2 Membrane Modes for Aeration

Membranes can be operated in two different modes. The dead-end mode, where

the membrane is pressurized with gas and one end of the fibers is sealed. In flow through

mode, gas is continuously pumped through hollow fibers and is vented to keep the partial

pressure of oxygen high along the membrane. The advantages of the dead end mode are

that the release of gases to the atmosphere is avoided and that 100 % gas transfer is

obtained since the only way the gas escapes is through diffusion through the membranes.

On the other hand, the disadvantages of this operation mode are condensation of water

inside the fiber membranes and the use of low pressures in order to obtain bubble less

aeration affecting the mass transfer rate (Ahmed and Semmens, 1992).

When operating membranes in flow through mode, vapor condensation is avoided

inside the membrane fibers and higher pressures can be utilized increasing the mass

transfer rate of a system. Since the gas is vented, complete transfer efficiency may not be

10

achieved and volatile organic compounds (VOC’s) may be stripped and vented to the

atmosphere. The VOC emissions present a concern due to their harmful effect to the

environment and the environmental compliance management costs. The process of

removing the VOCs from the environment is usually more expensive and troublesome

than avoiding the initial release of VOCs. Also, VOCs emissions present a definitely

unsafe environment in space.

HFMBRs have replaced conventional reactors for wastewater applications. The

presence of biofilm offers a higher rate of removal by the HFMBRs in comparison to

conventional treatment. Higher oxygen conversion when used with sealed end

membranes and high organic carbon removal rates can be achieved. The oxygen

diffusion rate is about 10 g/m2-d in conventional reactors while in HFMBRs up to 20

g/m2-d can be achieved (Torrey, 1984). HFMBRs can be used for simultaneous

nitrification and organic removal in a single reactor. Hollow fiber bioreactors are suitable

for simultaneous carbon substrate oxidation, nitrification (oxygen rich side of biofilm),

and denitrification (oxygen depleted biofilm) (Timberlake et al., 1988). However, a

microporous HFMBR for the sole purpose of nitrification was under scrutiny to complete

the objectives of this thesis.

2.3 Nitrification

Nitrification is a microbial process by which reduced nitrogen compounds

(primarily ammonia) are sequentially oxidized to nitrite ( −2NO ) and nitrate ( −

3NO ). This

is predominantly an aerobic chemoautotrophic process (Maier et al., 2000). Nitrifiers are

11

obligate aerobes that utilize oxygen (O2) for respiration and utilize inorganic carbon as an

energy source.

Nitrification is a two step process, typically involving two different types of

nitrifiers in the conversion of ammonia to nitrite and nitrate. True nitrifying bacteria are

considered to be those belonging to the family nitrobacteraceae. These bacteria are

strictly aerobic, gram-negative, chemolithic autotrophs. They require oxygen, utilize

mostly inorganic (without carbon) compounds as their energy source, and require carbon

dioxide (CO2) for their source of carbon. The energy sources are derived from the

chemical conversion of ammonia to nitrite, or nitrite to nitrate. Five genera are generally

accepted as ammonia-oxidizers and four genera as nitrite-oxidizers. Of these,

Nitrosomonas (ammonia-oxidizers) and Nitrobacter (nitrite-oxidizers) are the most

frequently identified genus (Watson et al., 1981).

In nitrification, first the oxidation of ammonia to −2NO (Eq. 2.1) is performed by

the Nitrosomonas, followed by the oxidation of −2NO to −

3NO (Eq. 2.2) by the

Nitrobacter species (Rittmann et al., 1994). For complete nitrification to occur, two

reactions must take place. Equation 1 shows the oxidation of ammonium to nitrite, and it

can be observed that two acid equivalents (H+) are created per mole of nitrogen oxidized.

Equation 2.2 shows the complete nitrification or conversion of the intermediate product

−2NO to −

3NO . Oxygen is required for the oxidation of ammonium and is used as the

terminal electron acceptor by the nitrifying bacteria.

12

+4NH + 1.5O2 → −

2NO + H2O + 2H+ Equation 2.1

∆G0 = -45.79 kJ per e- eq

−2NO + 0.5O2 → −

3NO Equation 2.2

∆G0 = -37.07 kJ per e- eq

The compound that gets oxidized is called the reductant and the substance that

gets reduced is called the oxidant. The oxidant is O2 and the reductant is +4NH ,

respectively (Rittmann and McCarty, 2001). Therefore, +4NH is the electron donor,

losing electrons to the electron acceptor O2, which gains an electron during the

nitrification process. When there is enough oxygen present, nitrification goes to

completion yielding −3NO ; however, an intermediate product is obtained when oxygen is

limiting in the reaction. It is important to remember that oxygen is not the only limiting

condition for nitrification, but that the carbon substrate can be limiting as well (Casey et

al., 1999). However, it can be observed from Equations 1 and 2, that the oxidation of

ammonium to nitrite is more energetically favorable in comparison to the second step in

nitrification. As a result, nitrite is fully consumed by bacteria in their environment

leading to predominantly the existence of nitrate (Rittmann et al., 1994).

Nitrification is an aerobic process that can occur not only in natural environments,

such as in lakes and rivers, but nitrification can be used for wastewater applications.

Nitrification can be accomplished in suspended or attached growth systems (Metcalf &

Eddy, 2003). Systems such as trickling filters, activated sludge, rotating biological

contactors, and packed beds have been used in the past. However, this research focuses

13

on nitrification occurring in attached growth systems, using membranes to increase

surface area per unit volume as composed to traditional attached growth systems.

The efficiency of the nitrification process is affected by the environmental

conditions (whether in environmental habitats or in a reactor), such as temperature, pH,

alkalinity, dissolved oxygen (DO), and nutrient availability (Udert et al., 2003). It has

been established that the rate of nitrification increases with increasing temperature.

Nitrification rates have been found to double for every 10°C increase in temperature

between 10°C and 30°C. According to Environmental Protection Agency (EPA)

findings, the pH levels below < 5.0, as well as pH > 8.0 have been reported to decrease

the rate of ammonium oxidation, decreasing the nitrification rates. Performance stability

is maintained at pH levels between 6.5 and 8.0. For complete nitrification to occur, the

amount of oxygen required is more than 4.57 g O2/g N, and certain wastewater

characteristics are necessary. At low DO concentrations (0.5 to 2.5 mg/L), nitrification

becomes limited (Metcalf & Eddy, 2003). A wastewater with low levels of organic

matter and the need of other micronutrients are also necessary in small amounts (P, S,

and Fe) for complete nitrification to occur.

In addition, factors such as membrane type and organic and hydraulic loading

have an effect on nitrification as well. Microporous membranes present higher surface

area per unit volume than silicone membranes. Synthetic membranes are thin, solid-

phase barriers that allow the passage of certain substances under the influence of a

driving force. Both the chemical and the physical nature of the membrane material

control membrane separation. Membrane separation occurs because of differences in

14

size, shape, chemical properties, or electrical charge of the substances to be separated.

Microporous membranes control separation by size, shape and charge discrimination,

whereas nonporous membranes depend on sorption and diffusion (Singh, 1998).

Nitrification depends on the surface area available for the attached

microorganisms, which are responsible for the conversion of ammonium to nitrate.

Nitrification is also dependent on the membrane permeability, which is dependant on the

membrane type for the diffusion of oxygen; in this case the electron acceptor. The

hydraulic loading, the rate at which the microorganisms are fed is also an important

factor to consider for high nitrification efficiency. These factors will be discussed in this

paper in subsequent sections.

Biological nitrogen removal by hollow fiber membrane bioreactors (HFMBRs) is

a promising method to remove nitrogen from wastewater. Nitrification in HFMBRs

occurs when the carbon substrate loading rate of the wastewater is low, and high oxygen

concentrations at the membrane-biofilm interface would support nitrification. A HFMBR

is used to accomplish nitrification for the removal of wastewater contaminants and the

possible use of this membrane process under microgravity conditions.

2.4 Transport Processes

There are three fundamental principles of transport processes. These mechanisms

are momentum transfer, heat transfer, and mass transfer. Momentum transfer is

concerned with the transfer of momentum, which occurs in moving media. Heat transfer

is concerned with the transfer of heat from one point to another, while mass transfer

15

involves the transfer of mass from one phase to another distinct phase (Geankoplis,

1983).

To determine a reactor’s performance, information on thermodynamics, physical

properties, hydrodynamics, and mass transfer must be known. In a HFMBR,

simultaneous mass transfer occurs. Gas diffuses through the membranes due to a

pressure differential, while at the same time, diffusion within the biofilm occurs due to

convective flow of the bulk liquid in the shell side of the reactor. Therefore, the overall

process involves diffusion of the gas through the membrane, transport from the bulk

liquid to the biofilm surface, diffusion through the biofilm, and transport of the liquid

from one point to another. Thus, the processes governing mass transport in HFMBRs are

mass transfer and hydrodynamics. The thermodynamic properties are assumed to be in

equilibrium.

In HFMBRs, the presence of packing provides a resistance to the flow of the fluid

that is greater than it would be in an empty column shell (Strigle, 1987). The non-

uniform distribution of the packing has an effect on liquid distribution of the flow as well

as gas velocity. It has been investigated in the past that the liquid flow is an active

element affecting the internal transport process in the anaerobic part of the biofilm

(Alphenaar et al., 1993); however, this has not been established due to several factors

affecting the hydrodynamics within the reactor. Parameters such as the mixing, residence

time distribution, and the influence of hydrodynamics on mass transfer are some factors

to take in consideration. Therefore, hydrodynamics and mass transfer are dependant on

each other.

16

2.4.1 Hydrodynamics

Mass transfer is influenced by the thickness of the membrane wall, the actual pore

diameter in the lumen, and the hydraulic flow through the membranes. The hydraulic

flow characteristics of complete-mix and plug-flow reactors can be described as varying

from ideal and non ideal, depending on the relationship of the incoming flow to outgoing

flow (Metcalf & Eddy, 2003).

A tracer may be used to recognize the hydraulic performance of a reactor. The

effect of short circuiting, channeling, flow patterns, and the actual residence time due to

biofilm growth can be determined by analyzing the tracer response curves. Moreover,

the tracer response curves may be used to estimate the biomass growth rates and the mass

transfer within the biofilm.

2.4.2 Mass Transfer

For a membrane system, the mass transfer process is determined by three mass

transfer resistances in series, resistance in the gas phase, the resistance due the membrane

and the resistance in the liquid. A HFMBR with microporous membranes was operated

for the purpose of this thesis. The membrane and gas resistances are considered much

smaller than the liquid resistance, thus neglected in the analysis for this report (Cote,

1989). Only the liquid mass transfer resistance is taken in consideration.

In HFMBRs simultaneous mass transfer occurs when oxygen diffuses through the

membranes within the reactor due to a pressure differential, and by forced convection

when nutrients are transported from the bulk liquid in the shell side of the reactor. Figure

17

2.1 shows the concentration profiles in the gas-membrane-liquid interfaces. Mass

transfer resistances are dependent on the hydrodynamic properties of the liquid phase and

packing structure. Resistances are smaller at larger, turbulent flows than at laminar

flows. Since mass transfer is dependent on the hydrodynamic conditions, and the

hydrodynamic conditions affect the biofilm growth within the HFMBR, the biofilm

thickness and structure affect the rate of mass transfer; therefore, affecting the overall

performance of the system.

Figure 2.1 Mass transfer in a nitrifying microporous HFMBR

Diffusion can be explained by Fick’s law and a mass transfer coefficient. Fick

proposed a linear relation between the rate of diffusion of a chemical species and the

local concentration gradient of that species (Cussler, 2002). The flux needs to be

18

calculated in order to determine the overall mass transfer coefficient. The flux, from

Equation 2.3 can be defined as the amount transferred per unit time, the flux (J).

)( cockJ −= Equation 2.3

where; J = flux of chemical at interface [M/V-T]

k = mass transfer coefficient [L/T] c = concentration of specie at interface [M/V] co = bulk concentration [M/V]

The flux, J, in Equation 2.3, includes both diffusion and convection. Mass

transfer across an interface is described in terms of a flux. Fick’s first law defines the

overall mass transfer coefficient as the sum of the three resistances in series, where the

value of each resistance is represented by its respective mass transfer coefficient. A

concentration differential is assumed and defined in Equation 2.4.

LMGO kkkk1111

++= Equation 2.4

where; 1/ Ok = overall mass transfer resistance [L/T]-1

1/ Gk = mass transfer resistance in the gas phase [L/T] -1 1/ Mk = mass transfer resistance through the membrane [L/T] -1 1/ Lk = mass transfer resistance in the bulk liquid [L/T] -1

The mass transfer resistance in the gas phase is determined by diffusion, and the

mass transfer in the liquid phase is determined by convection. Mass transfer has a strong

dependence on the biofilm structure, the hydrodynamic conditions, and substrate loading

on the biofilm surface (Viera et al., 1993). As previously stated, in a microporous hollow

fiber membrane reactor, the membrane and gas resistances are much smaller than the

19

liquid resistance, and considered negligible in mass transfer analyses of this type (Cote,

1989).

Additionally, Fick’s law takes in consideration the length and number of

membranes where diffusion is taken place; thus, the length and number of membranes

will be taken in consideration. From Equation 2.4 a new term, a diffusion coefficient (D)

and the membrane length (lm) are introduced.

lmcocDJ )( −

= Equation 2.4

where;

J = flux of chemical [M/V-T] D = diffusion coefficient [L2/T]

(c –co)= concentration difference [M/V] lm = membrane length [L] 2.4.3 Dimensionless Groups

Different correlations are used in order to express mass transfer. The Reynolds

number is the most important dimensionless number in fluid dynamics and provides a

criterion for determining dynamic similarity; the Reynolds number is used to determine

whether a flow will be laminar or turbulent. The Peclet number is a dimensionless

number relating the forced convection of a system to its heat conduction. Other

dimensionless groups such as the Schmidt and Sherwood numbers are also used in mass

transfer in general and diffusion in flowing systems calculations in particular. Table 2.1

provides the dimensionless groups used to express mass transfer (Cussler, 2002).

20

Table 2.1 Dimensionless numbers Dimensionless Groups Physical Meaning

Reynolds Number (Re = lυ0/υ) Forced convection Sherwood Number (Sh = kl/D ) Mass transfer velocity/ Diffusion velocity

Schmidt Number (Sc = υ/D ) Diffusivity of momentum/Diffusivity of mass Peclet Number (Pe = υ0l/D) Flow velocity/Diffusion velocity

2.5 Biofilms

Bacteria have an innate tendency to stick to surfaces, and the bacteria growing in

adherent, slime-encased communities are known as biofilms. A biofilm is then a layer of

organic matter and microorganisms formed by the attachment and proliferation of

bacteria on the surface of an object (Maier et al., 2000). Biofilms are important in the

engineering field due to their applications. Biofilms can be used in pollution control such

as in processes like trickling filters, rotating biological contactors, and anaerobic filters.

Hollow fiber membrane bioreactors (HFMBRs) are considered a relatively new

system for aerobic wastewater treatment. HFMBRs have the main advantage of high

oxygen transfer into biofilms and overcoming oxygen limitations while maintaining very

high oxygen conversion efficiencies leading to the treatment of high strength organic

wastewater. The main importance of biofilms, and that is the focus of these thesis, is the

use of biofilms in HFMBRs as a media for dual mass transfer to occur by the addition of

oxygen and substrates from opposite sides. The biofilm is used for the removal of

nitrogen compounds in the waste streams, known as nitrification.

21

2.5.1 Biofilm Development

Biofilm formation occurs in submersed non-sterile water or surrounded by a moist

environment. Biofilms are developed in two stages, reversible and irreversible

attachment, respectively. Reversible attachment is a transitory phase caused by

physicochemical attraction, and irreversible attachment is the actual biological

stabilization of the microorganisms (Maier et al., 2000).

A conditioning film is formed due the accumulation of organic dissolved

molecules of hydrophobic nature at the solid-liquid interface. This conditioning film is

an attractive environment for bacteria to accumulate. An initial adhesion is controlled by

the various attractive or repulsive physicochemical forces leading to passive, reversible

attachment to the surface. An irreversible attachment is a biological, time dependent

process related to the proliferation of bacterial exopolymers forming a chemical bridge to

the solid surface. By a combination of colonization and bacterial growth the mature

biofilm is formed (Marshall et al., 1985).

2.5.2 Biofilms in MABRs

The performance of biofilm processes is often diffusion limited. Substrate

removal and electron donor utilization occur within the depth of the attached growth

biofilm and subsequently the overall removal rates are a function of diffusion rates and

the electron donor and electron acceptor concentrations at various locations in the

biofilm. Dissolved oxygen concentrations of 0.5 to 2.5 mg/L can be considered limiting

for attached growth process (Metcalf & Eddy, 2003). However, in a system where

22

biofilm is absent from the membrane wall, bubble formation depends upon the flow

velocities within the gaseous and liquid phases and the degree of oxygen saturation in the

bulk aqueous phase (Cote et al., 1989).

A membrane aerated bioreactor was used to accomplish the objectives of this

research. Initially, the effect of mass transfer by the use of microporous membranes and

their application for microgravity conditions was evaluated. Also, a comparison of the

effect of membrane type and configuration on treatment efficiency to previous literature

values was performed, and finally the amount and distribution of biofilm growth within

the reactor were determined by utilizing a hollow fiber membrane bioreactor (HFMBR).

23

CHAPTER III

MATERIALS AND METHODS

The goal of this research was to (a) evaluate the effect of mass transfer by the use

of microporous membranes; and (b) compare the effect of membrane type and

configuration on treatment efficiency to previous literature values; and (c) determine the

amount and distribution of biofilm growth within the reactor. A microporous hollow

fiber membrane bioreactor (HFMBR) was used to complete the objectives. Results of

this study, if appropriate, will aid in the use of HFMBR for space applications.

3.1 Membrane Module

The HFMBR (Figure 3.1) was purchased from Liquid-Cel® Membrane

Contactors. There are 3600 hydrophobic polypropylene microporous membranes that

have 300 µm outer diameter and 200 mm long. The total surface area of the fibers is of

0.80 m2, and they have a porosity of 40 percent. The microporous membranes are located

inside a shell with an internal diameter of 31.75 mm and a length of 275 mm. The actual

measured working volume of the reactor was found to be of 63 mL. A summary of the

membrane properties is presented in Table 3.1.

The membrane module has inlet and outlet ports for the aqueous and gaseous

streams. The HFMBR was originally designed for the removal of oxygen from water and

other liquids. Water is pumped through the lumen side of the fibers, a vacuum is applied

to the shell side of the module, air diffusing from the water into the shell side of the

24

reactor. However, for this thesis, the reactor is used for aeration; water passes through

the shell side and pressurized air diffuses from the inside of the fibers into the water. The

microporous membranes within the HFMBR supply oxygen through the pores and serve

as a supporting structure for nitrification biofilm formation. Figure 1 shows a schematic

of the membrane bioreactor configuration.

Figure 3.1 Hollow fiber membrane reactor (HFMBR) schematic

25

Table 3.1 HFMBR characteristics Membrane Characteristics Porosity 40% Porosity OD/ID 300µm OD/220µm ID Potting Material Epoxy Number of Fibers 3600 Maximum Temperature/Pressure 2.8 kg/cm2 (2.8 bar, 40 psig) at 23 °C with appropriate

hose clamps. Maximum 30 °C at lower pressures Active Surface Area 0.5 m2 (5.4 ft2) Priming Volume (ID) 63 mL Housing Characteristics Material Polysulfone Flange Connections Shellside (Gas/Vacuum) Standard Female Luer Lock Supplied with two ⅛ inch

Hosebarb adaptors which mate to 1/4 inch ID tubing Lumenside (Wetted Surface) 1/2 inch Hosebarb Weight Dry 0.15 kg (0.32 lbs.) Liquid Full (Lumenside) 0.2 kg (0.44 lbs.) Shiping Weight 0.3 kg (0.66 lbs.)

3.2 HFMBR

3.2.1 Inoculation

Inoculation of the reactor was completed using nitrifying bacteria batch culture

originally obtained from the Texas Tech University-Water Recovery System. The

nitrifying bacteria were grown and acclimated in the batch culture. A known volume of

deionized, distilled water (DDI) was added as well as nutrients such as ammonium

chloride (NH4Cl), sodium bicarbonate (NaHCO3) and Winogradskys Medium Modified

(Atlas, 1995). The Winogradskys Medium Modified was selected for cultivation of

26

nitrifiers. The changes in the ammonia and nitrogen oxides ( −xNO -N, −

2NO -N, −3NO -N)

concentrations were monitored. Ammonia oxidation activity was observed by a decrease

in the ammonia concentration and an increase in the −xNO -N concentration, indicating the

presence and growth of nitrifiers. The batch was fed once or twice a week, depending on

the rate of ammonium conversion.

After assuring the presence of nitrifiers in the batch culture, the mixed solution

was added to the HFMBR. The reactor was continually fed with NH4Cl, NaHCO3, and

the Winogradskys Medium Modified. The inorganic feed was to support an autotrophic

population within the reactor. Continuous monitoring of the ammonium and nitrogen

oxides persisted, as well as other conditions suitable for the growth of nitrifiers, such as

pH and dissolved oxygen within the bioreactor.

3.2.2 Feed Composition

An inorganic solution was used to feed the HFMBR. The feed was prepared daily

and consisted of sodium bicarbonate, ammonium chloride, DDI, and a solution similar to

batch culture feed, in proportions presented in Table 3.2. The feed tank was kept

homogeneous using a stirring bar.

Table 3.2 Composition of HFMBR feed Ingredient Amount [g/L]

DDI 1 NaHCO3 1.25 NH4Cl 0.625

Winogradsky's Solution 20

27

3.3 HFM Reactor System

3.3.1 System Components

The HFMBR consisted of a pump, influent and effluent tanks, silicone tubing

lines to connect the system, a mass flow controller and a pressure gage to control the air

pressure into the system. Figure 3.2 gives a simplified layout of the operated HFMBR.

3.3.1.1 Pressure Measurement

Oxygen was delivered by the addition of air to one of the cavities in the reactor

(Figure 3.3). Air was supplied from TTU facilities. A mass flow controller

manufactured by Cole Parmer (Model A-32464-16) was used to maintain a constant air

pressure within the system, while a digital pressure gage (Cole Parmer model HW-

68920-00) was used to just measure the pressure. Air was supplied to the reactor at a gas

pressure of 3.44 kPa (0.5 psi). Air flow was opposite to the water flow.

3.3.1.2 Connections

Feed and effluent tanks were connected to the reactor by the use of silicone

tubing (peroxide) obtained from Cole Parmer Instrument Co. The feed was delivered to

the reactor by 4 feet (MASTERFLEX®, L/S ™ 14) silicone tubing. The effluent line,

with the same characteristics presented above was of a length of 1 foot. The lines were

periodically cleaned and replaced to ensure that biofilm growth did not occur in the lines

but within the reactor.

28

Figure 3.2 Hollow fiber membrane reactor system layout

Figure 3.3 HFMBR module

29

3.3.2 Analytical Methods

Daily influent and effluent water samples were taken from the reactor and

measured for pH, temperature, dissolved organic carbon (DOC), −2NO -N, −

3NO -N, NH3-

N, total dissolved solids (TDS), and dissolved oxygen. All nitrogen measurements are

reported as mg-N/L.

Dissolved oxygen concentrations were measured by using a ROSS probe

(ThermoOrion 9708). All samples were filtered through sterilized membranes with

0.45 µm pore size and samples were prepared following Standard Methods (APHA,

1998). Filtrates were tested for nitrate ( −3NO -N), nitrite ( −

2NO -N) and ammonia (NH3-

N). The samples were analyzed by ion chromatography (DX-600) Dionex, USA) for the

detection of −3NO -N and −

2NO -N, a TOC machine manufactured by Shimadzu (Model

TOC-V CSH) for the detection of TOC, while NH3 was analyzed by using a ROSS probe

(ThermoOrion 9708).

3.4 Loading Studies

The performance of the HFMBR was related to the +4NH -N loading rates for

nitrification. Different loading rates were used to determine the reactor’s maximum

nitrification efficiency. The maximum nitrification efficiency within the HFMBR was

determined by analyzing the concentrations of NH3-N and −xNO -N (in mg/L) in the

influent and effluent of the system.

30

The nitrifying HFMBR was operated for approximately eight months. The feed

concentration was kept constant throughout the HFMBR operation; however, the loading

(flow) rate, at which the feed (mass ammonia fed to nitrifiers) was applied to the reactor,

changed over time. The HFMBR was operated at seven different hydraulic retention

times (HRT) including 0.15, 0.09, 0.07, 0.06, 0.04, 0.03, and 0.026 days, respectively.

After reaching steady state conditions, the loading rate (mg/day) was changed.

The need to keep the loading rates within the oxygen transfer capabilities of the

system was necessary for successful treatment of the HFMBR. The best removal

efficiency is expected at high HRTs (low flow rates) where there is enough contact time

for nitrification to occur. On the other hand, poor efficiency is expected at low HRTs

(high flow rates) where the microorganisms have little contact time for the removal of

NH3-N from the system.

Factors such as the hydrodynamics within the HFMBR influence treatment as

well as the biofilm growth and thickness in the reactor; for simplicity all these factors are

assumed to be constant throughout the experimental procedure. The reactor optimum

nitrification efficiency was therefore determined under two conditions: (1) by

determining the best loading rate for nitrification to occur, and (2) by determining the

effect of biofilm growth on mass transfer limitations.

3.5 Nitrification

Nitrification rates can be calculated by the ammonia removal rates, and the

amount of nitrite and nitrate produced. The reactor was fed with inorganic carbon to

31

support a pure culture of autotrophic bacteria; therefore, the heterotrophic population was

considered negligible. A nitrogen mass balance of the system was performed to calculate

the nitrification efficiency of the HFMBR. The ammonia oxidation percentage was

obtained by dividing the effluent nitrite plus nitrate concentration by the influent

ammonia concentration. The system performance, for −2NO -N, −

3NO -N, and ammonium

( +4NH -N) concentrations, was compared at different hydraulic retention times.

Nitrification within the system was calculated for each test point. Daily

measurements for influent NH3-N and effluent −xNO -N ( −

2NO -N + −3NO -N)

concentrations were considered. The measured NH3-N concentrations were converted to

+4NH -N in order to estimate the nitrification efficiency. Percent nitrification was

calculated using Equation 3.1.

(inf) N-NH

)eff( N-NO

4

-x

+=ionNitrificat Equation 3.1

3.6 Hydrodynamics/Tracer Studies

Tracer studies are useful to evaluate the hydraulic performance of a reactor.

Experiments were conducted on the reactor during the initial (no biofilm present) and

final (biofilm present) phases. Sodium bromide was used as a conservative tracer in a

continuous input tracer study. Sodium bromide was injected into the system at different

flow rates. Collection of influent and effluent samples continued until the effluent

bromide concentration matched the influent bromide concentration. Samples were

32

analyzed using automated ion chromatography (IC) and all values were reported as

(mg-Br/L).

The use of a tracer was used to recognize the dynamic behavior of fluid flow

through the HFMBR. The effect of short circuiting, channeling, flow patterns, and the

actual residence time due to biofilm growth were determined by analyzing the tracer

response curves. Moreover, the tracer response curves may be used to estimate the

biomass growth rates and the mass transfer within the biofilm. The number of

membranes in the reactor has an effect on the active surface area for biofilm growth

influencing the treatment efficiency. Replicates of the experiments were performed by

using different fluid flows. Hydrodynamic analyses were evaluated by using the data

collected during tracer studies at the initial (no biofilm present) and final (biofilm

present) stages of the bioreactor operation.

3.7 Mass Transfer Experiments

Oxygen was required as the terminal electron acceptor for respiration of the

microorganisms. The number of membranes in the reactor has an effect on the active

surface area for biofilm growth, directly influencing treatment efficiency. A negligible

membrane resistance for oxygen transfer is assumed due to the micro-porous size of the

membranes. Therefore, the only resistance to mass transfer is provided by the bulk

liquid. Previous research, done by Yang and Cussler (1989), had already established that

the majority of the resistance when using microporous membranes, was from the bulk

liquid.

33

To calculate the mass transfer within the hollow fiber membrane bioreactor

(HFMBR), aeration experiments were conducted. DDI was boiled and sparged with

nitrogen gas until the dissolved oxygen (DO) concentration was below 1 mg/L. The

influent and effluent DO concentrations were measured using a ROSS probe

(ThermoOrion 9708). The gas pressure was kept constant at 0.5 psi. Experiments were

conducted until saturation was reached. Experiments were conducted at different flow

rates and they were performed prior to biofilm formation, as well as after biofilm growth.

The effect of biofilm growth on mass transfer was then determined.

From the oxygen transfer experiments, the oxygen flux through the membranes,

mass transfer coefficients, and the diffusion coefficient were calculated and compared to

other researchers.

3.8 Biofilm Analysis

Biofilm growth was observed in the bioreactor. Determination of biofilm

distribution, thickness, and the determination of the bacteria present within the bioreactor

were objectives of this research. By analyzing the biofilm distribution throughout the

bioreactor, the hydrodynamics may be better understood.

To determine biofilm growth within the reactor, two different tasks were

accomplished: (1) the determination of biofilm distribution throughout the bioreactor, and

(2) the identification of the bacteria present within the biofilm. Sample strategies to

extract the biofilm attached to the membranes were developed.

34

The purpose of determining the biofilm distribution throughout the bioreactor was

to identify the preferential flow path, and predict the effect of biofilm formation on

hydrodynamics. A visual analysis was first completed. Biofilm distribution was

analyzed by obtaining the mass per surface area in the longitudinal direction and at four

different locations within the HFMBR circumference (Figure 3.4). Biofilm sampling was

accomplished in three different ways, in the longitudinal and circumferential direction

and from the outside towards the inside of the reactor, respectively.

Figure 3.4 Sampling locations within the HFMBR

35

3.8.1 Determination of biofilm distribution throughout the bioreactor

3.8.1.1 Circumferential analysis

Samples were obtained around the circumference of the reactor. Four samples

were necessary; each located 90° from each other. Refer to Figure 3.4 for sampling

strategy. Samples were obtained from the top (4 cm), middle (8 cm from top of reactor),

and 4 cm from the bottom of the reactor (Figure 3.5). This sampling strategy was used to

minimize errors and provide a better understanding of the effect of hydrodynamics on

biofilm distribution. A total of 12 samples were obtained from the three cross-sectional

areas. The longitudinal and circumferential sampling of biofilm would give an estimate

of the whole area and distribution covered by the biofilm.

3.8.1.2 Longitudinal Analysis

The biofilm growth in the longitudinal direction of the bioreactor was determined

to understand the biofilm distribution throughout the HFMBR. The flow characteristics

were determined by analyzing biofilm growth (mass per membrane surface area) in the

longitudinal direction. The reactor membranes have an approximate length of 20 cm;

therefore, five different samples were taken from different locations identified in Figure

3.4 (bacteria mass and volume).

36

Figure 3.5 Different cross-sections within the HFMBR

The biofilm thickness was also determined by extracting and freezing membranes

from the longitudinal direction. The membranes were analyzed under a Watec CCD

Camera (Edmund Optics VZM450 zoom lense) and a NI IMAQ ((PCI 1200 interface) for

image capture. The thickness was used to determine the density of biofilm present.

3.8.1.3 Outside-in Strategy

Taking in consideration the 3600 membranes within the reactor, samples were

taken from the outside towards the middle of the reactor. The initial idea was to samples

in bundles, and sample from the outside towards the center of the membranes. However,

no biofilm growth was observed in the inner membranes, within a distance of 0.5 cm

from the outer membranes. Due to the size and distribution of the membranes just one

sampling within the center of the reactor was performed. The membrane sampling can be

observed in Figure 3.6.

37

Figure 3.6 Membrane sampling

The last sampling strategy was used to estimate the effect of membrane locations

on biofilm density. Wet and dry masses, as well as the biofilm thickness were measured

to try to estimate biofilm density. A total suspended solids test was conducted following

the procedure in Standard Methods (APHA, 1998). Previously it has been observed that

hydrodynamics affects biofilm density. Assuming full flow contact through all the

membranes, a denser biofilm was assumed to be found within the inner membranes of the

HFMBR, where they are closely packed in comparison to the outside membranes.

3.8.2 Identification of the Bacteria Present within the Biofilm

The purpose of identifying the bacteria present within the bioreactor was to

distinguish between the autotrophic population (Nitrosomonas and Nitrobacter species)

and the possible presence of a heterotrophic population in the nitrifying reactor. In order

to identify the bacteria present within, the biofilm three different plating methods were

applied.

38

3.8.2.1 Identification of Heterotrophic Bacteria by Cultivation in Nutrient Agar

The HFMBR was fed with inorganic carbon during its operation. The presence of

an autotrophic bacteria population was therefore established by feeding inorganic carbon

into the system. However, heterotrophs are found everywhere, and their possible

presence was assumed. Thus, in order to identify the presence of heterotrophic bacteria

within the HFMBR a Nutrient Agar was selected for the identification of a wide variety

of microorganisms. The Nutrient Agar composition is presented in Table 3.3.

Table 3.3 Nutrient Agar Composition Ingredient Amount [g/L]

Beef Extract 3 Peptone 5

Agar 15 Preparation of Medium: Suspend 23 g of the powder in 1 L of purified water. Mix thoroughly. Heat with frequent agitation and boil for 1 min. to completely dissolve the powder. Autoclave at 121° C for 15 min.

3.8.2.2 Identification of Nitrobacter Species by AT5N Medium An autotrophic population was established by feeding inorganic carbon into the

system. In order to identify the presence of autotrophs within the system two different

mediums were taken in consideration, an AT5N Medium and the Winogradsy’s Medium,

Modified. The AT5N Medium was chosen over the Winogradsy’s Medium, Modified due

to the fact that suspended precipitates exist in the latter. The AT5N Medium was

therefore chosen for cultivation and maintenance of the Nitrobacter species and

Nitrobacter Winogradsky, respectively. Table 3.4 presents a detailed composition of the

39

Medium used. For the identification of the Nitrobacter species the original medium was

altered, as for the amount of CaCO3 (due to the hardness of the water in Lubbock) and the

agar added and the replacement of (NH4)2SO4 for an appropriate nitrite source, sodium

nitrite (NaNO2), respectively.

Table 3.4 AT5N medium composition Ingredient Amount [g/L]

CaCO3 1 NaNO2 1.5 K2HPO4 0.5 MgSO4 0.05 KHCO3 0.03

CaCl22H2O 0.02 Preparation of Medium: Add components to tap water and bring volume to 1.0 L. Mix thoroughly. Gently heat and bring to boiling. Distribute into tubes or flasks. Autoclave for 15min at 15 psi pressure 121° C.

3.8.2.3 Identification of Nitrosomonas Europaea by AT5N Medium The presence of the Nitrosomonas Europaea was determined by using the AT5N

Medium as well. The Nitrosomonas bacteria are in charge of the oxidation of +4NH -N to

−2NO -N, therefore is the first step for nitrification to reach completion. Thus, analysis for

the identification of these bacteria was accomplished by utilizing the AT5N Medium. The

medium was altered by addition of agar (15 g/L) for solidification and plating purposes

(Table 3.5).

40

Table 3.5 AT5N Medium Composition Ingredient Amount [g/L]

CaCO3 1 (NH4)2SO4 1.5

K2HPO4 0.5 MgSO4 0.05 KHCO3 0.03

CaCl22H2O 0.02 Preparation of Medium: Add components to tap water and bring volume to 1.0 L. Mix thoroughly. Gently heat and bring to boiling. Distribute into tubes for flasks. Autoclave for 15min at 15 psi and 121° C.

Three different plating media were therefore used for identification of autotrophic

and heterotrophic bacteria population. Two replicates of each media at two different

dilutions at the different locations (Figure 3.4) were considered to minimize errors. The

two different dilutions, 1:1 and 1:10, respectively, were used to simulate nutrient rich and

nutrient poor environments to obtain better determination of the presence and possible

bacterial count. Plates were incubated under 30°C for a period of two to seven days

depending on bacterial growth.

41

CHAPTER IV

RESULTS AND DISCUSSION

The objective of this research was to determine and compare the advantages and

disadvantages of a microporous hollow fiber membrane bioreactor (HFMBR) to silicone

membranes. The following discussion details the results obtained for the analysis of

hydrodynamics, mass transfer, biofilm distribution throughout the bioreactor, and the

overall bioreactor performance.

4.1 Nitrification

The change in nitrification capacity of the hollow fiber membrane bioreactor

(HFMBR) is observed in Figure 4.1. The influent +4NH -N concentrations are slightly

variable throughout the experiments due to variations in feed make up, which affect the

standard deviation and results obtained in this report. Conversely, a constant pattern,

where the effluent +4NH -N decreases as the −

3NO -N increases is observed, and relatively

constant −2NO -N concentrations were found throughout the operation of the bioreactor.

Greater concentrations of −3NO -N (mg/L) compared to −

2NO -N were found in the

effluent. This fact indicates that complete nitrification ( +4NH → −

2NO → −3NO )

conversion was achieved. An HRT of 0.15 days, showed the greatest +4NH -N conversion

to −3NO -N, which is attributed to the fact that greater nitrification is obtained at longer

HRTs.

42

Hydraulic Retention Time (days)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Con

cent

ratio

n (m

g/L)

0

50

100

150

200

250

300Initial NH4-N(mg/L)Final NH4-N(mg/L)Final NO2-N(mg/L)Final NO3-N(mg/L)

Figure 4.1 HFMBR conversion rates

The average influent and effluent concentrations of +4NH -N, −

2NO -N, and −3NO -

N are presented in Table 4.1. Nitrification within the HFMBR was calculated using the

averages from each test point at its corresponding hydraulic retention time. Table 4.2

shows a summary of the operating conditions and the results obtained while operating the

HFMBR.

43

Table 4.1 Evolution of nitrification process Av. Initial Av. Final Av. Final Av. Final Av. Final

NH4-N NH4-N NO2-N NO3-N NOx-N Retention

Time (days) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) 0.15 167.7 ± 17.2 84.3 ± 16.6 4.3 ± 3.0 101 ± 15.4 104.9 ± 16.0 0.09 144.8 ± 23.8 68.6 ± 15.5 43.4 ± 23.3 43.9 ± 21.9 87.3 ± 9.3 0.07 145.9 ± 22.0 82.2 ±12.2 13.9 ± 2.9 51.8 ± 6.5 65.7 ± 7.8 0.06 158.6 ± 12.5 97 ± 14.3 15.7 ± 4.2 46 ± 5.6 61.8 ± 7.4 0.04 169.9 ± 24.9 118.6 ± 19.8 12.9 ± 5.1 50.4 ± 10.0 62.3 ± 10.7 0.03 174.7 ± 16.2 122.9 ± 19.5 14.9 ± 4.3 28.6 ± 5.9 42.5 ± 7.2 0.026 168.2 ± 19.5 145.6 ± 18.3 9.2 ± 2.87 14.4 ± 2.5 23.6 ± 7.9

Table 4.2 presents the effluent characteristics for DO and pH. The DO

characteristics were found to be a function of the biofilm growth; however, this will be

discussed in detail in Section 4.4. On the other hand, the dissociation balance for

ammonium-ammonia is dependent on the temperature and pH (Tavares et al., 2001).

Optimal nitrification rates occur at pH values in the 7.5 to 8.0 range. However, a

pH of 7 to 7.2 is normally used to maintain optimum nitrification rates (Metcalf and

Eddy, 2003). The HFMBR operated at a pH range between 7 and 8. The upper pH limits

were nearly reached (Table 4.2) when operating at 0.03 and 0.026 days, suggesting that

nitrification was insufficient within the HFMBR to lower the pH. This is believed to

affect the overall reactor performance where a sudden decrease in efficiency is observed

between the 0.03 and 0.026 HRTs. Influent and effluent pHs were compared at each test

points, a graphical pH representation can be found in Appendix B.

Tabl

e 4.

2 Ef

fluen

t res

ults

for H

FMB

R d

urin

gN

NH

4−

+ lo

adin

g Lo

adin

g 1

2 3

4 5

6 7

Day

s of O

pera

tion

143-

181

1-24

11

5-14

2 88

-114

25

-60

61-8

7 18

2-21

8 H

RT

(min

utes

) 21

0 12

6 10

5 90

63

42

37

HR

T (d

ays)

0.

15

0.09

0.

07

0.06

0.

04

0.03

0.

026

pH

7 ±

0.71

7.

01 ±

0.2

3 7.

67 ±

0.0

8 7.

66 ±

0.1

5 7.

56 ±

0.2

4 7.

801

± 0.

125

7.91

± 0

.12

DO

(m

g/L)

4.

29 ±

1.8

1 4.

13 ±

0.6

5 2.

4 ±

1.31

2.

21 ±

0.6

7 3.

41 ±

0.6

1 3.

46 ±

1.2

3.

06 ±

0.6

1

NO

x (m

g/L)

10

4.99

± 1

6 87

.34

± 9.

3 65

.72

± 7.

8 61

.76

± 7.

4 62

.26

± 10

.7

42.5

2 ±

7.2

23.6

± 4

.8

Vol

umet

ric L

oadi

ng

(g N

H4/m

2 -d)

0.94

2.

26

3.28

4.

85

10.6

1 24

.54

30.3

5

Vol

umet

ric

Con

vers

ion

Rat

e

(g N

Ox/L

-d)

4.94

11

.41

12.3

6 15

.81

32.5

3 49

.98

35.6

3

Con

vers

ion

Rat

e pe

r Su

rfac

e A

rea

(g N

Ox/L

-d)

0.59

1.

36

1.48

1.

89

3.89

5.

97

4.26

Rem

oval

Rat

e

(g N

H4/m

2 -d)

0.47

1.

07

1.85

2.

97

7.40

17

.27

26.2

7

Nitr

ifica

tion

Effic

ienc

y (%

) 74

.74

± 1

3 68

.87

± 13

.6

51.8

7 ±

10

44.1

7 ±

7.1

39.2

9 ±

10.4

28

.57

± 5.

3 15

.89

± 3.

4

44

45

From Figure 4.2 it can be observed that the percent of ammonia removed ranged

from 16 to 75 percent. The influent and effluent total dissolved solids were measured

during the data collection period (for more details refer to Appendix A). Since no

significant sloughing of the biofilm was observed, cell growth within the HFMBR was

assumed to accumulate during the experimental runs; thus, affecting the percent of

ammonia removed. Biofilm growth within the bioreactor is addressed in Section 4.5.


0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

% A

mm

onia

Con

vers

ion

0

20

40

60

80

100% Ammonia Conversion

R2 = 0.94y = -4.8+99.3*(1-e-16.8x)

Figure 4.2 HFMBR efficiency

As predicted, the HFMBR reached maximum NNH4 −+ conversion at low loading

rates and high HRTs. Low reactor performance was observed at low HRTs when there

was insufficient contact time between the NNH4 −+ in feed and the microorganisms;

46

minimal biological reactions occurred and low nitrification was observed suggesting

kinetic limitations within the HFMBR. Figure 4.2 indicates that 75 percent ammonia

conversion was achieved at a HRT of 0.15 days; however, ammonia conversion was

found to reach saturation between 69 and 75 percent. Therefore, a statistical analysis

was performed (a t-test at 99% and 95% confidence intervals), and it was observed that a

sufficient statistical difference existed between the two flow rates (0.15 and 0.09 days),

indicating that the test point with an HRT of 0.15 days cannot be rejected (Appendix E).

The experimental data from Figure 4.2 was used to obtain an empirical bacterial

growth relationship. A curve was fitted to best estimate nitrification or ammonia

conversion with respect to HRT. Thus, from the relationship in Figure 4.2 the true

intercept of the curve would be negative (-4.8). At very low HRTs low to no treatment

would occur; therefore, there is a minimum HRT necessary for nitrification to occur,

which in this case was found to be 0.03 days. This graph would aid in the determination

of an operating flow rate for a needed percent ammonia conversion within a bioreactor.

A detailed discussion would involve an understanding of the microbial kinetics process,

but this subject is beyond the scope of this thesis. The ammonia conversion within the

HFMBR was found not only to be affected by the loading rates, but also the reactor

configuration and packing density.

The stoichiometric parameters for the nitrification process were calculated using

Equation 4.1 where the ammonium ( NNH4 −+ ) influent concentration and the effluent

NNOx −− and NNH4 −

+ were taken in consideration and agreed with the results found.

(out)NHN(out)NOCl(in)NH 4x4+− +−→− Equation 4.1

47

Table 4.3 summarizes the ammonia removal rate from various nitrification

systems compared to the rate obtained from the HFMBR. Metcalf and Eddy (2003)

reported maximum surface specific nitrification rates for tertiary nitrification trickling

filter to be in the range of 1.2 to 2.9 g N/m2-d. It can be observed that the HFMBR offers

a reasonable minimum degree of ammonia removal rate (0.47 g NH4-N/m2-d). However,

in comparison to conventional treatment and other hollow fiber membrane bioreactors,

the microporous HFMBR is capable of providing higher NNH4 −+ removal rates. A

maximum nitrification rate of 26.27 g NH4-N/m2-d was achieved; therefore, the HFMBR

presents a suitable option for the replacement of conventional treatment in wastewater

applications.

Table 4.3 Ammonium-nitrogen removal rate from various treatment systems

Source Nitrification Rate (g NH4-N/m2-d) Reference

0.15-0.43 van Rijn and Rivera [1990] 0.24-0.55 Kamstra et al. [1998] 0.28-0.69 Nihof and Bovendeur [1990] 0.6-0.73 Bovendeur et al. [1990]

Tricking filter

0.94-3.92 Greiner and Timmons [1998] 0.43 Wickins [1985] Submerge biofilter 0.59 Davis and Arnold [1998]

Sequencing batch reactor 1.86 Zhu and Chen [1999] Porous gas permeable

membrane 1.1-3.1 Suzuki et al. [2000]

2.2 Yamagiwa and Ohkawa [1994] 0.023-3.0 Hibiya et al. [ 2003]

HFMBR

0.47-26.27 This work

48

4.2 Loading Studies

The overall objective of the loading studies was to optimize bioreactor efficiency.

The bioreactor was operated continuously for eight months at seven different NNH4 −+

loadings. The hydraulic retention times at which the reactor was operated were 0.15,

0.09, 0.07, 0.06, 0.04, 0.03, and 0.026 days. An increase in NNH4 −+ conversion with

increasing hydraulic retention time (HRT) was shown in Figure 4.1. Even though

maximum NNH4 −+ conversion was achieved at a HRT of 0.15 days, Table 4.2 shows that

maximum conversion per unit volume of reactor was achieved at a HRT of 0.09 days.

An increase in the ammonia conversion rate (g/L-d) was expected with increasing

HRT. However, volumetric conversion rates (g/LR-d), where LR is the volume of the

reactor, decrease with increasing HRT. This is due to the fact that at large HRTs there is

low ammonia loading rate per unit volume of the reactor (i.e., low flow ∴low mass

input). Although the concentration of ammonia removed is higher at high HRTs, the

actual mass removed per day is higher at low HRTs.

Figure 4.3 shows a different trend in comparison to Figure 4.2 where the percent

of ammonia conversion increases with increasing HRT. As expected, Figure 4.3 shows

maximum conversion of ammonia at an HRT of 0.03 days (volumetric NNH4 −+ loading

24.54 g NH4/m2-d). However, a sudden decrease in reactor performance is observed at

an HRT of 0.026 days (37 minutes). The decrease in reactor performance is due to the

fact that the reactor was kinetically limited, i.e., contact time between the substrate and

microorganisms was not long enough to sustain growth. A decrease of 50 percent in

conversion rate (15.81 g NOx/L-d) was observed at an HRT of 0.06 days in comparison

49

to a conversion rate of 32.5 g NOx/L-d at 0.04 days. Thus the decrease in reactor

performance was attributed to the microbial kinetics, which is beyond the scope of this

thesis.

Hydraulic RetentionTime (days)

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Vol

umet

ric C

onve

rsio

n R

ate

(gN

Ox/

L-da

y)

0

10

20

30

40

50

60Ammonia Conversion

R2 = 0.88

y = 79.6e-22.8x

Figure 4.3 Volumetric conversion rates

An empirical relationship was obtained from the calculated data. Volumetric

conversion rates were mathematically correlated to its dependency on HRT. The data

best fit was an exponential decay relationship. Maximum conversions would occur at

low HRTs. Maximum NNH4 −+ conversion would be reached at an HRT of zero, but

this is non-realistic; therefore, 79.6 volumetric conversion would be never achieved.

A total surface area of 0.5 m2 (3600 fibers within HFMBR) was used when

calculating the conversion rates per membrane surface area, assuming uniform flow

50

throughout the reactor and full contact between the flow and fibers. Figure 4.4 shows the

conversion rate per surface area plotted against HRT, which shows the same behavior

obtained when analyzing the reactor conversion rate per unit volume. Maximum

conversion per surface area was achieved at 0.03 days with a loading rate of 24.54 g

NH4/m2-d.


0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Con

vers

ion

Rat

e pe

r Sur

face

Are

a (g

NO

x/m

2 -d)

0

2

4

6

8

10Ammonia Conversion

Figure 4.4 Conversion rates per surface area

The HFMBR was able to achieve ammonia conversion efficiencies in the range of

16 to 75 percent. Better efficiencies were obtained at long HRTs. A maximum

conversion rate efficiency of 75 percent was achieved at a loading rate of 0.94 g NH4-

N/m2-d. The corresponding NNH4 −+ removal rates ranging from 0.47 to 26.27 g NH4-

51

N/m2-d. The performance characteristics in terms of ammonium removal rates and

efficiency of the HFMBR are summarized in Figure 4.5.

Loading Rate (g NH4-N/m2-d)

0 5 10 15 20 25 30 35

Am

mon

ia C

onve

rsio

n (%

)

0

20

40

60

80

100

Ammonia conversion (%)

Rem

oval

Rat

e (g

NH

4-N

/m2 -d

)

0

10

20

30Removal Rate (g NH4-N/m2-d)

30% Ammonia Conversion

18 g NH4-N m2-dQ = 0.035 days

Figure 4.5 Overall reactor performance

From Figure 4.5 it can be observed that removal rate per surface area increases as

the loading rate increases (low HRTs). A maximum removal rate of 26.27 g NH4-N/m2-d

is observed at an HRT of 0.026 days. The loading rate is directly proportional to the

HRT, where more mass is put into the system at low retention time or high flow rates and

a higher removal rate is obtained. However, it is also observed that high conversion rates

are obtained at low HRTs; hence, a compromise or optimum operational point between

the two processes is necessary for the development of an ideal system.

52

Figure 4.5 also presents a comparison between the removal rate per surface area

and the percent of ammonia conversion obtained by the HFMBR. From this graph, the

optimum operational point can be assumed to exist at a loading rate of 18 g NH4-N /m2-d.

This assumption was made based on the fact that obtaining high percent of ammonia

conversion would involve operating the reactor at low HRTs, which is not a feasible

option because this would require either very low hydraulic loading rates or high reactor

volumes to treat the expected amount of wastewater. Also, operating the reactor to obtain

maximum mass removal rates would consequently generate very low percent of ammonia

removed from the system, thus giving an unacceptable effluent quality.

The HFMBR performance and removal rates shown in previous graphs were

calculated assuming uniform biofilm distribution throughout the bioreactor. During

experimental analyses performed near the completion of the HFMBR operation (Section

4.5), it was observed that about ¼ of the total membrane surface area was utilized for

biofilm growth. Biofilm distribution concentrated at influent and effluent ends of the

reactor, and an uneven biofilm distribution throughout the length and diameter was

observed.

A comparison of removal rates between the total and effective surface areas used

for the removal of NNOx −− is presented in Figure 4.6. The removal rate in g NNOx −

−

was calculated for each test point. A constant influent NNH4 −+ (g) was assumed to

calculate the effective (900 membranes) removal rates per surface area. A summary of

the initial and final masses for each different test point is presented in Appendix A. The

effective removal rates at three different HRTs were used (i.e., 0.03, 0.07, and 0.15 days),

53

using 900 membranes is shown in Figure 4.6. Note the effective removal rates are

greater than the conversion rates calculated assuming complete usage of the total number

of membranes within the HFMBR. Greater removal rates per surface area were obtained

with fewer membranes, indicating that the reaction rate per surface area per membrane is

the limiting factor for increasing conversion efficiency of the bioreactor.

Number of tubes

0 500 1000 1500 2000 2500 3000 3500 4000

Con

vers

ion

Rat

e pe

r Sur

face

Are

a (g

NO

x/m

2 -d)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6HRT = 0.15 days HRT = 0.07 daysHRT = 0.03 days

Figure 4.6 Conversion rate comparison

Based on the biofilm distribution within the HFMBR (Section 4.5) the actual

efficiencies were calculated using 900 membranes (note that this number was estimated

from the biofilm analysis; however the actual surface area could be less than estimated).

A maximum removal efficiency of 75 percent was obtained at a HRT of 0.15 days, using

54

¼ of the assumed actual surface area available (0.132 m2). If the total 0.5 m2 of the 3600

membranes within the bioreactor was used, higher removal rates would be obtained, in

turn improving the reactor overall performance.

Table 4.4 shows a summary of the different removal efficiencies obtained per

surface area. Removal rates would increase depending on the surface area available for

biofilm formation for treatment to occur. Therefore, from Figure 4.7 it can be observed,

assuming uniform biofilm coverage throughout the bioreactor that greater removal

efficiency would be obtained with an increase in surface area. However, reactor

efficiency would still depend on the HRT. This would aid in the design of HFMBRs for

NNOx −− removal and the optimization in reactor performance.

Table 4.4 Mass removed at a constant rate % Mass removed Hydraulic Retention

Time (days) 450 Membranes 900 Membranes 3600 Membranes 0.15 31.31 74.74 250.48 0.09 30.15 68.87 241.22 0.07 22.52 51.87 180.13 0.06 19.47 44.17 155.75 0.04 18.32 39.29 146.58 0.03 12.17 28.57 97.34 0.026 7.01 15.89 56.12

55


0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

Mas

s Rem

oved

%

0

100

200

300

400% Removed using 450 membranes% Removed using 900 membranes% Removed using 3600 membranes

Figure 4.7 Comparison of the HFMBR removal efficiencies

4.3 Hydrodynamics

Hydrodynamics allow for understanding of the dynamic behavior of fluid flow

through a bioreactor, affecting mass transfer and overall reactor efficiency. In this study,

the effect of hydrodynamics on nitrification efficiency was investigated. The hollow

fiber membrane bioreactor (HFMBR) was found to operate under plug flow conditions

and to have low dispersion, i.e., a Reynolds Number less than 3.0 and dispersion number

less than 0.05, respectively (Metcalf & Eddy, 2003).

Loading rate experiments were conducted at seven different flow rates including,

0.3, 0.5, 0.6, 0.7, 1.0, 1.5, and 1.7 mL/min. Initial and final tracer experiments were

performed at three different flow rates (0.3, 1.0, and 15 mL/min). Initial tracer studies

56

refer to experiments performed on the bioreactor without biofilm formation; final tracer

studies are the experiments performed after all loading rate experiments and after biofilm

formation. The results of the initial flow through hydrodynamic analysis without biofilm

are presented in Figure 4.8.

The results of the experiments without biofilm support mathematical calculations,

proving that reactor flow regime can be represented by a plug flow behavior and no

mixing or dispersion occur within the HFMBR. From Figure 4.8, an initial lag is

observed for all three data sets, forming a smooth s-shaped curve. At a flow rate of 15

mL/min, an initial lag of approximately 5 minutes is observed, while lags of 50 minutes

and 180 minutes occur for flow rates of 1.0 mL/min and 0.3 mL/min, correspondingly.

Complete recovery of the tracer (NaBr) was achieved in all cases; however, 90%

recovery was achieved around 90 min for a 15 mL/min flow rate, 120 min for 1 mL/min,

and 450 minutes for a flow rate of 0.3 mL./min.

57

Time (min)

0 200 400 600 800 1000

C/C

o (m

g-B

r/L)

0.0

0.2

0.4

0.6

0.8

1.0

Q = 0.3 mL/min, HRT = 210 minQ = 1 mL /min, HRT = 63 minQ = 15 mL/min, HRT = 4.5 min

Figure 4.8 Hydrodynamic experiments without biofilm

In comparison to the s-shape curve seen in Figure 4.8, Figure 4.9 shows an

exponential shape curve formed by the data set due to the absence of a lag time for tracer

studies conducted after biofilm development. The absence of a lag time for the final

experiments was expected due to biofilm growth within the HFMBR. As channeling

occurs, fluid flow seeks preferential paths through regions of lower packing, reducing the

working volume of the reactor and decreasing the overall HRT. However, according to

Bao and Limpscomb (2002), areas of low packing experience less mass transfer (high

KL) while areas with high packing density experience high mass transfer (low KL). This

will be addressed in detail in Section 4.4.

58

Time (min)

0 200 400 600 800 1000

C/C

o (m

g-B

r/L)

0.0

0.2

0.4

0.6

0.8

1.0

Q = 0.3 mL/min, HRT = 210 minQ = 1 mL/min, HRT = 63 minQ = 15 mL/min, HRT = 4.5 min

Figure 4.9 Hydrodynamic experiments after biofilm growth

Recovery of about 90% of the Br concentration (mg/L) takes place around 150

minutes for a flow rate of 1 mL/min in comparison to 450 minutes at a flow rate of 0.3

mL/min. In comparison to the initial tracer studies, the tracer experiments after biofilm

formation show a delay in time for 90% recovery at both flow rates while the same

recovery time (90%) is observed at a flow rate of 15 mL/min, which is due to the force of

convection. Complete recovery of the tracer was not obtained during the hydrodynamic

experiments conducted after biofilm formation. Figure 4.9 also shows the occurrence of

tailing after reaching the theoretical HRT at each flow rate, indicating that short circuiting

occurred within the HFMBR due to the formation of biofilm. Although, complete

recovery was not achieved at each HRT; a longer experimental time would overcome this

problem.

59

The residence time following biofilm growth was determined by analyzing the

tracer response curves. In Figure 4.9 the tracer response curves show a decrease in HRT

for the final tracer studies (no initial lag time). This is due to the formation of biofilm

within the HFMBR. The new HRTs at 0.3, 1.0, and 15 mL/min flow rates were

determined to be 73.5, 22.1, and 1.6 minutes, respectively, thus biofilm growth within the

bioreactor was found to replace approximately 35% of the total working volume of the

HFMBR. Therefore, biofilm growth during the loading rate experiments affected the

reactor HRT and hydrodynamics, as the complex geometry and flows affected the

experimental mass transfer and reactor performance.

When a liquid is introduced into a bioreactor the axial dispersion becomes an

important factor on the reactor performance. Predicted values for this effect are given in

Table 4.5. The unitless dispersion number approaches infinitive (d >1) indicating high

dispersion. Also, the Peclet number (Pe = ul/D), representing the ratio of the mass

transport brought about by advection and dispersion, was found to be less than 1

indicating that dispersion is the dominant factor in mass transport (Metcalf & Eddy,

2003).

Table 4.5 Dispersion in the HFMBR Dispersion without biofilm Dispersion after biofilm growth

Flowrate Coefficient

of Axial Dispersion

Unitless Dispersion

Number

Peclet Number

Coefficient of Axial

dispersion

Unitless Dispersion

Number

Peclet Number

[mL/min] [m2/sec] [-] [-] [m2/sec] [-] [-] 0.3 1.31E-05 7.03 0.14 2.02E-05 10.85 0.09 1 6.65E-05 10.71 0.09 1.00E-04 16.11 0.06 15 1.00E-03 10.74 0.09 1.90E-03 20.41 0.05

60

Analyses were also performed after biofilm formation within the HFMBR. The

morphological characteristics of biofilms (biofilm thickness, biofilm density and biofilm

surface shape) are very important for the overall performance of a biofilm reactor. These

characteristics strongly affect the biomass hold-up (biofilm attachment in a bioreactor)

and mass transfer in a biofilm reactor (Garrido et al., 1997; Tijhuis et al., 1995). The

biofilm formed would increase the dispersion within the HFMBR, having a direct effect

on the achievable biomass concentration in the reactor, and consequently on the overall

mass transfer rate. The hydrodynamics influences biofilm development, as well as the

biofilm influences the hydrodynamics. Biofilm analyses will be discussed in Section 4.5.

As biofilm density increases, local mass transfer decreases and bulk dispersion increases.

This is misleading, though because local dispersion is dynamic and may increase or

decrease, depending on the type of system.

Table 4.5 also shows greater dispersion occurring after the formation of biofilm.

This was expected due to biofilm growth. However, the unitless dispersion numbers

were found to be much greater than 1 (d ∞→ ); therefore, considered negligible due the

hydraulic characteristics of the HFMBR. At high unitless dispersion numbers, a reactor

is assumed to be ideal (approaching CFSTR behavior); however, the HFMBR was found

to behave as a plug flow. Therefore, the model used for this research was assumed to be

inappropriate to model the HFMBR. Thus, the size and membrane configuration of the

bioreactor, as well as the inflow velocity and its fluctuations had an effect on the results

obtained; indicating that the convective flow dominates and controls the mass transport

61

within the HFMBR. An incentive exists to develop a model for a membrane system with

more favorable system hydrodynamics to improve the overall reactor efficiency.

4.4 Mass Transfer

The mass transfer characteristics of polypropylene microporous hollow fiber

membranes for the oxygenation of water were studied. Three different resistances in

series are typically taken in to consideration (Equation 2.4). The model used for this

study follows the model presented by Yang and Cussler (1986) where Equation 2.4 is

simplified by neglecting the gas film and membrane resistance. When microporous

membranes are used, the gas pressure is maintained below the bubbling points and

oxygen is transported through the pore system rather than the through the polymer (Cote,

1989; Kreulen et al., 1993). The mass transfer coefficients for oxygen vary with water

flow rate but not with gas flow rate, implying that the mass transfer coefficient in the gas

phase does not contribute to the overall mass transfer (Yang and Cussler, 1986).

The membranes within the HFMBR were considered heterogeneous, composed of

the membrane material (polypropylene) and pores, 60 and 40 percent, respectively.

Further, the membranes were hydrophobic, and so the membrane pores filled with gas;

thus, the major resistance to mass transfer was expected to be the liquid resistance. The

membrane mass transfer (KM) is a function of the membrane properties (permeability),

the characteristic membrane thickness and Henry’s law constant. The polypropylene

permeability was found to be 5.69*10-19 mol/m-s-Pa; for which, KM was found to be

negligible (Appendix C). Therefore, as expected, mass transfer occurred through the

62

pores and not through the membranes. It is important to mention that bubble-less

aeration was not achieved during the experiments without biofilm. The formation of

bubbles was observed in the bulk liquid due to some water penetration within the lumen

of the membranes. The results of the initial mass transfer experiments without biofilm

are presented in Table 4.6; it can be observed that the liquid mass transfer remains

relatively constant throughout the four different test points (i.e., water flow rates 0.3, 1.0,

10, 15 mL/min), and is the only and dominating factor in the overall mass transfer

coefficient (KO).

Table 4.6 HFMBR mass transfer without biofilm Flowrate RL= 1/ KL KO Sh JE [mL/min] [min/m] [m/min] [-] [mmol-DO/sec-m2]

0.3 8.37E+04 1.19E-05 20 6.46E-04 5 8.37E+04 1.19E-05 20 1.12E-05 10 8.37E+04 1.19E-05 20 7.77E-04 21 6.69E+04 1.49E-05 25 1.00E-03

Table 4.7 shows the total oxygen transfer into the bulk liquid. The total oxygen

transfer into the bulk liquid is the sum of the measured DO in the effluent and the oxygen

consumed by the microorganisms. The oxygen consumed by the microorganisms was

estimated using Equation 4.2. From Metcalf & Eddy (2003), the biological oxidation of

oxygen is represented by Equation 4.2 for which it can be noted that for each g of

ammonia nitrogen (-N) converted, 4.25 g of O2 are utilized.

→+++20.098CO21.863O4NH Equation 4.2

+++−+ 1.98HO20.0941H30.98NO2NO7H50.0196C

63

Table 4.7 Oxygen transfer within the HFMBR

Flow rate (mL/min)

HRT (days)

Position in

Sequence

Initial DO

(mg/L)

Final DO

(mg/L)

Biofilm Oxygen consumption

(mg/L)

Oxygen Transfer (mg/L)

0.3 0.15 6 6.3 4.29 0.35 4.64 0.5 0.09 1 6.01 4.13 0.32 4.45 0.6 0.07 5 6.34 2.4 0.27 2.67 0.7 0.06 4 6.49 2.21 0.26 2.47 1 0.04 2 7.2 3.41 0.22 3.63

1.5 0.03 3 7.08 3.46 0.22 3.68 1.7 0.026 7 6.24 3.06 0.10 3.16

As the flow rate increases, the HRT decreases, thus the oxygen transfer from the

lumen side of the membranes into the bulk liquid was expected to decrease with

decreasing HRT. A decrease in oxygen transfer is observed for the initial four

operational points; however, the oxygen transfer increases at flow rates 0.04, 0.03, and

0.026 days, respectively. This decrease in oxygen transfer is related to the nitrification

efficiency obtained by the HFMBR. The variation of oxygen transfer with HRT is shown

Figure 4.10. A definite trend is not observed, which is attributed to the scatter (Table

4.7).

64


0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

DO

(mg/

L)

0

1

2

3

4

5Oxygen transfer (mg/L)

R2 = 0.3y = 10.9x + 2.7

Figure 4.10 Oxygen transfer within the HFMBR

Table 4.8 presents the mass transfer coefficients obtained after biofilm formation

within the HFMBR. Bubble-less aeration was achieved for the final mass transfer

experiments due to the formation of biofilm. The oxygen flux was calculated (JE) by

performing mass transfer experiments (change in oxygen concentration per time per

surface area). As expected, a decrease in the measured oxygen flux in the bulk liquid was

observed after biofilm formation. The decrease in flux did not consider the oxygen

consumed by the microorganisms. The experimental data just indicates the amount of

excess oxygen passing through biofilm (i.e., oxygen flux).

65

Table 4.8 HFMBR mass transfer after biofilm formation Flowrate R = 1/kL ko Sh # JE JM [mL/min] [min/m] [m/min] [-] [mmol-DO/sec-m2] [mmol-DO/sec-m2]

0.3 1.26E+05 7.97E-06 13 2.8E-04 7.20E-04 1 1.26E+05 7.97E-06 13 5.3E-04 4.93E-03 10 4.18E+04 2.39E-05 40 1.9E-04 NA

The flux or oxygen consumption by the bacteria (JM) was estimated at different

flow rates assuming uniform growth throughout the bioreactor. At flow rates of 0.3 and

1.0 mL/min, the total oxygen flux (J = JE + JM) was found to increase with biofilm growth

(Table 4.8); however, this increase was of less than an order of magnitude, which was

considered insignificant. According to Semmens et al. (2001), biofilm growing on the

surface area of a membrane, can accelerate or retard oxygen flux across the membrane

but it always reduces the rate of oxygen transfer to the external bulk liquid. Biofilm

growth within the HFMBR was found to accelerate the oxygen transfer. The bioreactor

configuration was considered to play an important role in these findings. Results are

presented in Appendix C.

The results obtained coincide with findings obtained by Wickramasinghe et al.

(1992) who analyzed the effect of mass transfer in various hollow fiber geometries and

Yang and Cussler (1986) who analyzed the design of hollow fiber contactors. The

HFMBR consisted of 3600 membranes which were believed to be closely packed

creating major channeling within the bioreactor (Section 4.3); channeling was expected to

increase with biofilm growth. Therefore, mass transfer was affected by the uneven fiber

spacing (due to biofilm growth) and major channeling through the closely packed fibers.

66

Nonetheless, oxygen fluxes are still a function of fluid velocity and substrate

concentration and this effect can be seen at a flow rate of 10 mL/min for which the

boundary layer or liquid resistance is reduced (Table 4.8). Mass transfer at high flow

rates after biofilm formation within the HFMBR was not enhanced due to the contact

time between the feed and microorganisms, the reactor size, and membrane

configuration. Convective flow becomes the governing force in mass transfer at high

flow rates. However, the bioreactor performance is not optimum due to kinetic limations;

therefore, operating the bioreactor at such high flow rates is not recommended.

The presence of biofilm was expected to increase the oxygen flux through the

membranes. As biofilm thickness increases, a greater external interfacial area is available

for the flux of substrate into the biofilm; therefore, mass transfer is increased (Semmens

et al., 2001). The effect of increasing biofilm thickness on mass transfer goes beyond the

scope of this thesis; however, Table 4.8 shows that the simple formation of biofilm did

increase oxygen flux.

Table 4.9 presents the dimensionless numbers calculated before and after biofilm

formation. The Sherwood (Sh) number is used to express mass transfer with force of

convection; it represents the ratio of the mass transfer coefficient in the liquid times the

characteristic length to the diffusivity of oxygen in water (at 20°C, D = 1.97810-9 m2/s).

The Peclet (Pe) number relates the forced convection of the system to its heat conduction

and is defined as the ratio of the fluid velocity times the characteristic length of the

reactor to the dispersion coefficient. The Schmidt (Sc) number is dimensionless

parameter used for mass transfer; it is defined as the ratio of the kinematic viscosity to the

67

mass transfer diffusion coefficient. The Schmidt number remains unchanged at all flow

rates; this is due to the negligible resistance of the membrane for which the diffusion

coefficient equals the oxygen diffusivity in water.

Table 4.9 Dimmensionless numbers Without biofilm After biofilm formation

HFMBR flow rate Re

Unitless Dispersion

Number Pe Sc Re

Unitless Dispersion

Number Pe Sc [mL/min] [-] [-] [-] [-] [-] [-] [-] [-]

0.3 0.24 7.03 0.14 509.14 0.24 10.85 0.09 509.14 1 0.81 10.71 0.09 509.14 0.81 16.11 0.06 509.14 15 12.13 10.74 0.09 509.14 12.13 20.41 0.05 509.14

A summary of the dimensionless numbers obtained after biofilm formation is also

presented in Table 4.9. The Peclet number was found to decrease after biofilm growth.

This was expected since Pe is inversely proportional to the dispersion coefficient, which

was found to increase with biofilm growth (Section 4.3). On the other hand, the Sc

number remained unchanged before and after biofilm formation. This was attributed to

the negligible resistance of the membrane for which the diffusion coefficient equals the

oxygen diffusivity in water.

Mass transport data were correlated using the common Sherwood dimensionless

relationship.

0.33nScmReSh = Equation 4.3

where;

m = constant [result of different packings] n = exponent of the Reynolds number for the empirical correlation

68

Figure 4.11 shows the variation of the mass transfer controlled by the liquid phase

before and after biofilm formation. The liquid mass transfer coefficient (KL) is

incorporated in the Sh number and the Reynolds (Re) number in this study is laminar (0.2

< Re < 12). At low Re, i.e., low flows, the Sherwood number was found to linearly

increase. The linear relationship obtained from Figure 4.10 allowed the determination of

“m” and “n” from Equation 4.3. It can be observed that before biofilm formation, the

linear relationship obtained in Figure 4.11 does not follow the tendency given by the

Sherwood correlation (Equation 4.3). The results indicate a system poor in turbulence,

but that some mass transfer influence or additional resistances in the liquid phase

probably exist. On the other hand, the relationship obtained after biofilm formation

shows a more approximate mass transfer relationship in comparison to previous studies

for which the performance of the HFMBR is controlled by the mass transfer in the liquid

phase (Yang and Cussler, 1986).

69

Re (dvL/v)

0 2 4 6 8 10 12 14 16 18

Sh(K

Ll/D

)/(Sc

(v/D

))0.

33

0

2

4

6

8

10

12Initial Experimental DataFinal Experimental Data

Figure 4.11 Sherwood vs. Reynolds number. Before and after biofilm formation

Figure 4.11 also shows the variation in Sherwood number with Reynolds number

after biofilm growth. A closer 1:1 relationship is obtained after biofilm growth, which

supports a stronger correlation where the mass transfer in the HFMBR was controlled by

the liquid phase. However, this is not true when operating at high flow rates; mass

transfer was found to be controlled by convection. The experimental data obtained after

biofilm formation was found to agree with results obtained by other researchers (Krudsen

and Katz, 1958; Wickramasinghe and Han, 2002; Yang and Cussler, 1986) as shown in

Table 4.10.

70

Table 4.10 Comparison of mass transfer correlations from literature Reference Correlation Re Range

Knudsen & Katz Sh = 0.022Re0.6Sc0.33 - Wickramasinghe & Han Sh = 0.39Re0.59Sc0.33 -

Yang & Cussler Sh = 1.25(Rede/l)0.93Sc0.33 5-3500 This Study

Before biofilm Sh = 2.45Re0.043Sc0.33 0.2-12 After biofilm formation Sh = 1.49Re0.45Sc0.33 0.2-12

4.5 Biofilm Analysis

The effect of hydrodynamics on the development of biofilm during the HFMBR

operation was analyzed. By determining the biofilm coverage and distribution within the

membranes in the bioreactor, the hydrodynamics may be understood. Sampling of the

reactor occurred at eight different locations within the circumference of the bioreactor. A

top view of the reactor and its cross-sectional sampling locations can be observed in

Figure 4.12. The biofilm analysis was divided in five different sub-sections. Initially, a

visual analysis was performed followed by, a circumferential and longitudinal biofilm

distribution analysis, respectively. Sections 4.5.4 and 4.5.5 describe biofilm thickness

throughout the bioreactor and the bacteria identification within the biofilm.

71

Figure 4.12 Sampling locations within the HFMBR

4.5.1 Visual Analysis

A non-uniform biofilm distribution within the HFMBR was observed. The

packing density and configuration of the membranes within the HFMBR have been found

to have an effect on biofilm formation, thereby affecting hydrodynamics. It was

hypothesized, according to Figure 4.12, greater biofilm growth around the influent port,

located at the bottom of the reactor, as well as closer to the effluent port, located at the

top of the reactor. High cell growth is dependent on the access to nutrients, which as

expected, in this case would be higher at the influent port. Growth, however, would be

affected by the shear forces presented by fluid flow; therefore, a denser and thinner

72

biofilm would be encountered at the ports. Longitudinal biofilm distribution was

assumed to be dependent on the preferential flow path, and minimal within the HFMBR.

By visual inspection, a more dense and dark biofilm was observed at the bottom

of section 2A of the reactor, coinciding with the influent port. All biofilm at the top of

the reactor was of a light brown color and seemed less dense, “flakey,” in comparison to

the biofilm formed at the bottom of the bioreactor. It was concluded that biofilm

distribution was greater at the top and bottom of the HFMBR, the latter being larger.

Biofilm distribution in the longitudinal direction was relatively uniform depending on the

membrane location. But, the amount of biofilm in the longitudinal direction was less

than the bottom and top sections of the reactor.

Section 2B contained greater biofilm at the bottom of the reactor in comparison to

the top, and a relatively uniform biofilm thickness was observed in the longitudinal

direction. When analyzing Section 3B, an intermittent distribution and “chunks” of

biofilm were observed at the top and bottom of the reactor, while little to no biofilm was

observed in the longitudinal direction when compared to Section 2B. On the other hand,

Section 4B contained less biofilm overall, i.e., top, bottom and in the longitudinal

direction of the HFMBR. Finally, Section 5B was studied, and an intermittent biofilm

distribution was observed similar to that of Section 3B. This was expected due to the

locations of both sections, opposite from each other and at equal distances from the

influent and effluent points at the bottom and top, respectively. Overall, Section 3B

visually appeared to have more biofilm than section 5B. The non-uniform biofilm

distribution within the HFMBR may be observed in Figure 4.13.

73

Figure 4.13 Biofilm growth within different locations of the HFMBR

74

4.5.1.1 Biofilm Distribution. Outside-in Strategy

Biofilm growth was assumed to occur over the total surface area of the HFMBR

(3600 membranes). Due to the configuration and high packing density, biofilm growth

did not occur within the inner membranes. Samples were taken in bundles, between 50

and 100 membranes, to analyze the mass per surface area in the cross-sectional sections.

However, since biofilm growth was not visually observed within 0.5 cm from the outer

membranes, the inner membranes were not tested for mass or biofilm thickness. It is

important to mention that biofilm growth was not observed by visual inspection;

however, biofilm growth did occur within inner membranes of the HFMBR as indicated

by plating experiments (Section 4.5.4). Figure 4.14 shows a comparison of the biofilm

growth in the inner and outer membranes after the experimental analyses.

Figure 4.14 Outside-in strategy

75

4.5.2 Circumferential Analysis

The reactor was analyzed for biofilm growth at the top, middle, and bottom of the

reactor (Figure 3.5). Four different samples at each location were extracted for which the

attached biofilm was analyzed for mass measurements. Mass measurements per

membrane surface area were calculated by extracting about 1 cm of membranes at each

location and 0.5 cm from the outside-in. The membranes were rinsed and placed in

aluminum pans were the biofilm mass was measured after performing a total suspended

solids (TSS) analysis (APHA, 1998).

Table 4.11 summarizes the mass per surface area obtained for each location.

Replicates were not obtained due to the reactor size and limited amount of biofilm within

the HFMBR. The results obtained from the performed experiments agree with the visual

observations initially stated. Greater biofilm mass per membrane surface area was

obtained at the bottom of the reactor. A graphical representation is shown in Figure 4.15.

Table 4.11 Cross-sectional mass per surface area 2A 3A 4A 5A

Top Section (g/m2) 0.454 0.898 0.020 0.351 Middle Section (g/m2) 0.038 0.020 0.008 0.006 Bottom Section (g/m2) 2.135 2.506 0.201 0.385

76

0

2

4

6

8

10

2A2B

3A3B

4A4B

5A

BottomMiddle

TopLongitudinal

Bio

film

Dis

tribu

tion

(g/m

2 )

Sampli

ng Se

ction

s

Location

Figure 4.15 Biofilm distribution within the HFMBR

4.5.3 Longitudinal Analysis

The biofilm growth was in the longitudinal direction of the bioreactor; however,

full coverage was not observed. This unequal distribution of biofilm was believed to be

caused by the flow distribution of the feed. Table 4.12 presents the results obtained from

the longitudinal analysis.

77

Table 4.12 Longitudinal mass per surface area Location Mass per Surface Area (g/m2)

2A 7.781 3A 7.479 4A 1.448 5A 2.081

As expected, results showed more biofilm growth per surface area in the same

direction of the moving flow. Overall, greater and more uniform biofilm growth was

observed in Section 2A. Figure 4.15 also shows that biofilm growth occurred in the same

direction of the moving flow and slowly moved around the reactor. Section 4A had a

smaller amount of mass per surface area in comparison to the other sections analyzed

within the HFMBR.

4.5.4 Biofilm Thickness

Biofilm thicknesses were calculated by extracting membranes and analyzing the

biofilm at each location specified in Figure 4.16. For simplicity of this work, it was

assumed that all membranes within a specific location (within a distance of 1 cm) within

the HFMBR were uniformly covered by biofilm with the same thickness. The

membranes were analyzed under a Watec CCD Camera (Edmund Optics VZM450 zoom

lense) and a NI IMAQ (PCI 1200 interface) for image capture. The images were

analyzed, and the thicknesses were determined using MatLab. The average biofilm

thicknesses were taken in consideration for this analysis and are summarized in Table

4.13.

78

Location

2A 2B 3A 3B 4A 4B 5A 5B

Bio

film

Thi

ckne

ss (m

m)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7Bottom Thickness (mm) Middle Thickness (mm) Top Thickness (mm)

Figure 4.16 Biofilm thickness

Table 4.13 Biofilm thickness Location Top Thickness

(mm) Middle Thickness

(mm) Bottom Thickness

(mm) 2A 0.207 0.035 0.333 2B 0.232 0.033 0.292 3A 0.048 0.020 0.124 3B 0.001 0.002 0.456 4A 0.002 0.042 0.159 4B 0.036 0.010 0.061 5A 0.023 0.047 0.009 5B 0.001 0.101 0.129

From Figure 4.16, it can be observed that a thicker biofilm was formed at the

bottom of the reactor, which is as expected due to the higher concentrations of nutrients

closer to the influent port of the HFMBR. Figures 4.17 and 4.18 show some of the

thicknesses obtained when analyzing the membranes under a Watec CCD Camera.

79

It was noted that the uneven distribution of biofilm was due to flow

maldistribution. The influent feed was pumped in the reactor from the bottom of the

bioreactor (Figures 3.1, 3.3); therefore, the flow was unequally distributed through the

HFMBR. Biofilm formation was observed in the same direction of the moving flow;

therefore, the assumption of an existing preferential flow path was taken in consideration

for this analysis. Channeling due to biofilm formation on the membranes was also

assumed to have an effect on the hydrodynamic behavior within the bioreactor.

Biofilm thickness was also found to be greater at the bottom of the reactor, which

supports the theory that the biofilm is affected by nutrient consumption. Nutrient

concentrations decrease as the fluid passes through the reactor; therefore, it can be

assumed that thinner biofilms would be found along the fluid’s path. However, this was

not the case shown in Figure 4.16; it was attributed primarily to the assumption of

uniform thickness within a sampling section (1 cm) and due to the possible sampling

errors when performing the experimental analysis.

Figures 4.17 and 4.18 present the different biofilm thickness at different locations

within the HFMBR. However, as expected, more biofilm grew around the bottom of the

reactor. These results suggest that the shear forces due to velocity affected biofilm

structure (Casey et al., 2000). Nevertheless, these results coincide with Gibbs and Bishop

(1995) who state that the velocity of the bulk fluid flow is one factor affecting the biofilm

thickness and density where higher velocities result in compressed (or thinner)

concentration of the biofilm. Biofilm density is not presented in this thesis due to the

sampling methods used and high error probability.

80

Figure 4.17 Biofilm thickness of sections 2A and 3A

81

Figure 4.18 Biofilm thickness of sections 4A and 5A

82

The purpose of determining the biofilm distribution throughout the bioreactor was

to identify the preferential flow path, and to predict the effect of biofilm formation on

hydrodynamics. Due to the high number of membranes and the packing density, flow did

not pass by all the membranes; the fluid flow was found to contact the outer membranes,

like in an annulus. The hydrodynamics were meant to be understood by analyzing the

biofilm growth; however, no definite conclusion was obtained. The biofilm was assumed

to affect the flow pattern, but it could be concluded that the flow pattern also affected the

biofilm growth within the HFMBR. Results have shown that the HFMBR did not operate

at maximum capacity. The loading rates, mass transfer, and hydrodynamics have been

affected by the bioreactor configuration; therefore, not operating at maximum efficiency.

4.5.5 Bacteria Identification

The reactor feed was composed of inorganic carbon in order to support an

autrotrophic population. Due to biofilm structure and heterogeneity, the possible

presence of a heterotrophic population was assumed. Samples were extracted from four

different locations at three cross-sectional areas, at the top, middle, and bottom of the

bioreactor (Figures 4.11 and 3.5). Two different medias were used to identify the

bacteria within the HFMBR, a Nutrient Agar and a AT5N Medium, for identification of

heterotrophic and autotrophic microorganisms, respectively.

Bacterial plates were made at two different dilutions (1:10 and 1:1) in order to

have better identification. Plates were incubated for 5 days; however rapid growth was

observed on the nutrient plates (heterotrophs) after 2 days while no growth was observed

83

for the nitrosomonas and nitrobacter species. As expected, heterotrophs grew faster than

autotrophs; however, the plates were incubated for the same period of time (5 days).

For all sections, heterotrophs, nitrosomonas, and nitrobacter species were found

to exist within the HFMBR. Heterotrophs were found even though the feed consisted of

inorganic carbon. The presence of heterotrophs was attributed to the initial feed used,

which contained of urine. The existence and survival of the heterotrophic population

within the HFMBR can be explained by the fact that these microorganisms fed on the

dead autotrophic bacterial cells. However, the fact that more colonies were observed

within the plates was considered to be a function of incubation time. Greater growth

occurred due to a larger incubation period of time instead of a larger population existing

within the bioreactor. Although, plate counts were beyond the scope of this thesis, a

greater population of nitrosomonas species was expected in comparison to the

nitrobacter specie. As previously mentioned, the feed consisted of inorganic carbon

(NH4Cl), which is the energy and carbon source for this specie, as opposed to −2NO -N for

nitrobacter specie.

84

CHAPTER V

CONCLUSIONS

A commercial microporous hollow fiber bioreactor (HFMBR) was analyzed for

wastewater treatment applications. The goal of this research was to (a) evaluate the

effect of mass transfer by the use of microporous membranes; (b) compare the effect of

membrane type and configuration on treatment efficiency to previous literature values;

and (c) determine the amount and distribution of biofilm growth within the reactor.

Results of this study, if appropriate, will help determine the use of the HFMBR in space

applications.

Loading rates and nitrification studies were performed in order to determine the

reactor’s optimum performance. High nitrification efficiencies can be obtained due to the

high surface area presented by the use of the microporous membranes in a HFMBR. In

this thesis, due to the high packing density and configuration of the bioreactor, the total

membrane surface area was not utilized and the reactor did not operate at its maximum

removal efficiency. However, for aeration purposes, the HFMBR may be appropriate for

wastewater treatment if the configuration is arranged to where the packing density is

reduced by increasing the spacing between membranes. Therefore, increasing the surface

area available for biofilm growth in the reactor would increase the removal efficiency,

being more suitable for wastewater treatment. If membrane spacing is not improved an

increase in reactor volume would be another option to consider for wastewater treatment.

However, for space applications, this would not be a recommended option due to

85

NASA’s requirements to reduce mass and volume of treatment systems owing to space

limitations.

Mass transfer within the HFMBR would also aid in the determination of the

design and overall reactor’s performance. The microporous membranes within the

HFMBR were considered to provide a negligible mass transfer resistance; thus, the

HFMBR has been found to provide better mass transfer in comparison to a membrane

system for which the membrane resistance is taken in consideration. Bubble-less aeration

was not achieved during the initial experiments without biofilm; however, bubbles were

not observed after biofilm formation. Mass transfer improved after biofilm formation

due to higher oxygen flux diffusing in to the biofilm increasing the total flux or mass

transfer of the bulk liquid.

The correlations between the oxygen mass transfer and fluid dispersion were

considered for the reactor performance. The bioreactor hydrodynamics were affected by

the reactor configuration, the number of membranes, and flow velocity. The effect of

flow velocity on reactor performance was mainly of interest for mass transfer analysis.

Flow velocity influenced mass transfer in the diffusion boundary layer thickness at the

biofilm liquid interface and biofilm density. Convective flow was found to be the

controlling factor on the rate of mass transfer due to the reactor size and packing density.

Uneven biofilm distribution was also found to affect the hydrodynamics of the bioreactor

due to channeling; thus, fluid flowed through preferential paths in regions of lower

packing, reducing the working volume and overall performance of the bioreactor.

86

In the HFMBR biofilm formation, thickness and density were proven to be

dependent on the fluid velocity and bioreactor configuration for which, uneven mass,

density, and thickness were observed. The morphological characteristics of biofilms such

as thickness, density, and shape are very important for the overall performance of a

biofilm reactor. These characteristics strongly affect the mass transfer in a biofilm reactor

and overall reactor performance. The biofilm heterogeneity also played an important role

in the reactor performance. The presence of a heterotrophic and autotrophic (nitrifiers)

was identified. Maximum growth was achieved by the nitrifiers as a maximum 75%

conversion rate was achieved. Maximum growth rate would not vary; however, higher

conversion rates would be achieved by increasing the nitrifying population, which will

increase conversion rates and bioreactor performance.

The advantages and disadvantages of using parallel distributed microporous

membranes within the HFMBR were analyzed. Microporous membranes in a HFMBR

present the advantage of increasing oxygen transport through the membranes in

comparison to silicone membranes. The use of parallel membranes at high packing

densities might not enhance the mass transfer in comparison to random membranes due

to biofilm formation and channeling. Short circuiting caused by channeling did occur

within the HFMBR; nevertheless, microporous membranes present higher surface area

for biofilm formation, presenting a better choice for high mass transfer to occur and high

ammonia removal rates.

The HFMBR is capable of achieving maximum nitrification efficiency at low

loading rates and high HRTs. Due to the reactor’s size, the HFMBR presents promising

87

use in space applications. These characteristics offer a potential for NASA’s needs;

nonetheless, developing a system with more favorable system hydrodynamics would aid

to improve treatment efficiency in a HFMBR.

Considering the above, it is recommended that to adequately demonstrate the

effectiveness of HFMBRs for wastewater applications under microgravity conditions a

comparison of the performance of several units is still needed. Research on the effect of

different membrane models, analyzing membrane geometry (parallel vs. random

membranes) should be addressed. Also, the determination of best operating pressure

without bubble formation, and the effect of increasing temperature for the enhancement

of treatment are factors to consider.

.

88

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94

APPENDIX A

RAW DATA DURING THE HFMBR STUDY

95

Table A1. Test point 1. Influent Concentrations (mg/L)

Date Day pH TDS DO NH3-N NO2-N NO3-N NOx-N 17-Aug 1 7.85 2238.00 7.17 129.42 1.23 1.23 18-Aug 2 7.80 2459.00 5.35 212.72 3.41 3.41 19-Aug 3 7.85 2287.00 6.74 149.52 1.88 1.88 20-Aug 4 7.87 2164.00 7.44 113.50 2.36 2.36 21-Aug 5 7.82 2460.00 7.22 136.76 1.59 1.59 22-Aug 6 7.80 2423.00 6.55 132.94 4.14 4.14 23-Aug 7 7.83 2264.00 137.35 4.49 4.49 24-Aug 8 7.83 2270.00 124.76 2.31 0.43 2.74 25-Aug 9 7.78 2163.00 7.01 133.13 2.49 2.49 26-Aug 10 7.78 2202.00 6.15 144.96 2.42 2.42 27-Aug 11 7.78 2245.00 7.01 133.13 2.10 2.10 28-Aug 12 7.83 2295.00 6.77 164.98 3.16 3.16 29-Aug 13 7.85 2292.00 6.56 153.02 2.91 0.27 3.18 30-Aug 14 7.83 2279.00 6.80 142.99 1.45 1.45 31-Aug 15 7.87 2150.00 6.09 127.22 1.25 1.25 1-Sep 16 7.88 2178.00 6.33 122.69 1.15 1.15 2-Sep 17 7.83 2408.00 5.56 123.69 1.18 1.18 3-Sep 18 7.85 2233.00 6.29 103.56 1.16 0.68 1.84 4-Sep 19 7.87 2278.00 6.71 122.50 1.68 1.68 5-Sep 20 7.86 2265.00 6.29 114.35 3.98 3.98 6-Sep 21 7.89 2224.00 5.99 130.67 1.69 1.89 3.58 7-Sep 22 7.86 2240.00 6.24 102.68 0.39 0.39 8-Sep 23 8.43 2169.00 0.97 176.85 1.42 2.09 3.51 9-Sep 24 8.28 2141.00 0.95 149.46 1.86 1.86

Average 7.88 2263.63 6.01 136.79 2.15 1.07 2.38 Std.Dev 0.15 92.77 1.71 23.88 1.06 0.85 1.10

96

Table A2. Test point 1. Effluent Concentrations (mg/L)

Date Day pH TDS DO NH3-N NO2-N NO3-N NOx-N Nitrification

17-Aug 1

18-Aug 2 7.43 2147.00 5.46 81.74 73.10 6.78 79.88 39.76

19-Aug 3 6.90 2078.00 57.22 87.69 6.98 94.67 67.04

20-Aug 4 6.90 1952.00 4.00 55.40 79.77 11.20 90.97 84.86

21-Aug 5 6.79 1827.00 5.00 45.24 68.60 18.87 87.47 67.72

22-Aug 6 6.99 2025.00 4.38 49.66 77.09 31.21 108.30 86.26

23-Aug 7 7.83 2018.00 3.54 58.04 68.76 42.16 110.92 85.51

24-Aug 8 6.83 1917.00 47.31 45.74 36.21 81.95 69.55

25-Aug 9 6.84 1917.00 4.95 61.39 44.48 40.90 85.38 67.91

26-Aug 10 6.91 1829.00 5.09 80.55 39.60 36.37 75.97 55.49

27-Aug 11 6.73 1841.00 4.73 81.86 43.26 36.44 79.71 63.39

28-Aug 12 6.78 1864.00 4.01 97.04 46.27 38.61 84.88 54.47

29-Aug 13 7.03 1933.00 3.51 87.54 40.43 39.26 79.69 55.14

30-Aug 14 6.90 1953.00 3.31 83.33 38.92 42.85 81.77 60.54

31-Aug 15 7.01 1919.00 4.05 67.31 35.08 42.73 77.82 64.76

1-Sep 16 6.97 1817.00 4.37 59.64 32.53 49.51 82.03 70.79

2-Sep 17 6.91 1854.00 3.57 56.83 27.01 53.35 80.35 68.79

3-Sep 18 7.21 2004.00 3.73 41.04 25.93 57.84 83.76 85.64

4-Sep 19 7.04 1906.00 4.40 53.59 22.25 75.37 97.62 84.38

5-Sep 20 7.03 1928.00 4.11 55.47

6-Sep 21 7.12 1940.00 3.78 60.98 25.99 70.51 96.50 78.19

7-Sep 22 7.02 1893.00 3.84 52.68 12.64 76.58 89.22 92.01

8-Sep 23 7.10 1914.00 2.82 83.94 9.84 73.64 83.48 49.98

9-Sep 24 7.04 1911.00 4.20 72.67 9.08 80.05 89.13 63.14

Average 7.01 1929.87 4.14 64.80 43.37 43.97 87.34 68.88

Std.Dev. 0.23 81.75 0.65 15.54 23.30 21.94 9.32 13.66

97

Table A3. Test point 2. Influent Concentrations (mg/L) Date Day pH TDS DO NH3-N NO2-N NO3-N NOx-N

10-Sep 25 7.82 2282.00 7.36 144.38 1.41 3.27 4.69 13-Sep 28 7.85 2195.00 5.83 159.31 0.00 0.00 0.00 14-Sep 29 7.87 2142.00 6.24 135.77 2.50 4.65 7.15 15-Sep 30 7.92 2282.00 152.28 2.51 4.16 6.66 16-Sep 31 7.85 2259.00 7.31 147.28 2.79 3.47 6.26 17-Sep 32 7.85 2096.00 7.69 148.46 1.64 0.00 1.64 18-Sep 33 7.83 2188.00 9.33 144.95 1.53 1.65 3.18 20-Sep 35 7.78 2251.00 7.19 211.79 1.77 2.52 4.28 21-Sep 36 7.82 2230.00 7.53 199.92 1.30 1.27 2.58 22-Sep 37 7.82 2202.00 8.14 1.68 2.11 3.80 23-Sep 38 7.84 2268.00 6.87 1.92 1.92 24-Sep 39 7.70 2366.00 6.94 1.09 0.32 1.41 27-Sep 42 7.80 2344.00 6.54 2.65 2.65 28-Sep 43 7.82 2199.00 6.97 1.49 1.49 29-Sep 44 7.82 2123.00 7.86 1.92 0.29 2.21 30-Sep 45 7.82 2215.00 7.02 217.83 4.08 2.42 6.50 1-Oct 46 7.87 2261.00 6.98 195.42 2.08 1.40 3.48 2-Oct 47 7.92 2280.00 7.54 203.08 1.31 0.06 1.38 4-Oct 49 7.92 2233.00 7.07 161.86 1.08 1.08 5-Oct 50 7.91 2221.00 6.02 179.92 1.66 0.13 1.78 6-Oct 51 7.90 2278.00 7.05 196.20 1.61 0.23 1.85 7-Oct 52 7.90 2297.00 7.97 161.78 1.50 1.50 8-Oct 53 7.85 2331.00 7.18 175.72 4.35 4.18 8.54 9-Oct 54 7.86 2271.00 7.15 166.96 2.84 0.33 3.17

11-Oct 56 7.94 2296.00 6.54 153.71 1.37 1.37 12-Oct 57 7.91 2300.00 7.54 179.22 15-Oct 60 7.90 2637.00 7.31

Average 7.86 2261.00 7.20 160.46 1.68 2.13 3.22 Std. Dev. 0.05 98.63 0.71 24.90 0.93 1.62 2.24

98



10-Sep 25 8.59 1897.00 3.72 78.72 6.45 83.49 89.94 65.96

13-Sep 28 7.58 1807.00 3.86 95.44 7.05 28.91 35.96 23.90

14-Sep 29 7.59 1960.00 3.91 103.17 11.54 54.34 65.88 51.38

15-Sep 30 7.51 1905.00 88.65 11.79 54.31 66.11 45.96

16-Sep 31 7.42 2022.00 3.06 121.17 14.22 52.66 66.89 48.09

17-Sep 32 7.36 1961.00 2.88 112.78 13.76 56.91 70.67 50.41

18-Sep 33 7.42 1852.00 3.59 105.82 10.99 52.38 63.37 46.29

20-Sep 35 7.63 2039.00 4.41 155.47 9.93 41.52 51.45 25.72

21-Sep 36 7.56 2029.00 3.24 146.76 12.40 45.96 58.37 30.91

22-Sep 37 7.54 2006.00 3.69 12.94 43.34 56.28

23-Sep 38 7.49 1954.00 1.98 15.97 43.87 59.84

24-Sep 39 7.44 2006.00 3.24 22.73 46.89 69.62

27-Sep 42 7.72 2356.00 1.51 17.44 51.91 69.36

28-Sep 43 7.54 2127.00 3.96 21.35 44.61 65.96

29-Sep 44 7.36 1941.00 3.33 24.43 47.80 72.23

30-Sep 45 7.31 1863.00 3.56 145.07 22.56 38.68 61.23 29.76

1-Oct 46 7.37 1941.00 3.66 128.51 26.05 47.25 73.30 39.72

2-Oct 47 7.60 2011.00 3.36 117.18 16.60 47.86 64.46 33.61

4-Oct 49 7.57 2022.00 3.52 129.01 16.90 47.54 64.44 42.15

5-Oct 50 7.56 1968.00 4.04 115.31 19.03 47.39 66.42 39.09

6-Oct 51 7.65 2029.00 3.45 129.77 15.28 41.24 56.52 30.50

7-Oct 52 7.58 2046.00 3.46 102.46 15.87 42.83 58.70 38.42

8-Oct 53 7.55 2058.00 3.70 125.25 13.05 36.18 49.23 29.66

9-Oct 54 7.42 2079.00 3.28 130.79 15.96 42.82 58.78 37.28

11-Oct 56

12-Oct 57 7.48 2025.00 3.25 120.41 16.68 47.44 64.13 37.89

15-Oct 60 7.87 2058.00 4.01 8.79 30.83 39.63

Average 7.56 1994.96 3.41 112.00 12.48 50.38 62.26 39.30

Std. Dev. 0.24 104.63 0.61 19.89 5.11 10.05 10.70 10.41

99


16-Oct 61 7.91 2541.00 5.93 163.93 18-Oct 63 7.94 2475.00 7.46 141.80 2.20 1.20 3.40 19-Oct 64 7.86 2575.00 7.44 3.13 1.35 4.47 20-Oct 65 7.78 2511.00 5.42 152.15 2.79 1.83 4.62 22-Oct 67 7.86 2529.00 6.07 2.61 1.33 3.93 23-Oct 68 7.88 2641.00 6.48 190.18 2.53 1.09 3.63 25-Oct 70 7.90 2630.00 7.95 168.80 2.81 0.09 2.90 26-Oct 71 7.95 2590.00 6.96 159.71 2.77 0.20 2.97 27-Oct 72 7.85 2583.00 6.22 157.68 1.53 0.04 1.58 28-Oct 73 7.88 2585.00 7.29 151.73 2.76 1.47 4.23 29-Oct 74 7.85 2517.00 7.85 145.04 1.79 1.35 3.13 30-Oct 75 7.92 2594.00 8.15 154.24 2.17 1.81 3.98 31-Oct 76 7.84 2600.00 9.09 160.69 1.68 0.81 2.49 1-Nov 77 7.78 2587.00 6.20 174.42 1.13 1.13 2-Nov 78 7.85 2496.00 7.80 1.36 0.15 1.52 3-Nov 79 7.76 2642.00 6.16 190.05 1.63 0.17 1.80 4-Nov 80 7.83 2623.00 7.88 157.27 1.09 0.41 1.50 8-Nov 84 7.96 2432.00 7.32 152.25 2.62 0.05 2.67 9-Nov 85 7.90 2460.00 7.46 170.83 0.84 0.08 10-Nov 86 7.83 2648.00 6.41 181.35 1.86 0.99 11-Nov 87 7.87 2575.00 7.19 198.36 1.71 Average 7.87 2563.52 7.08 165.03 2.30 1.05 2.94 Std. Dev. 0.05 62.81 0.91 16.26 0.68 0.65 1.13

100



16-Oct 61 7.96 2426.00 3.49 11.89 28.33 40.22

18-Oct 63 7.91 2244.00 4.62 107.86 9.95 24.27 34.21 25.55

19-Oct 64 7.83 2324.00 4.31 11.42 26.40 37.83

20-Oct 65 7.79 2397.00 3.82 132.15 13.54 25.66 39.21 27.28

22-Oct 67 7.72 2226.00 2.89 14.27 28.49 42.76

23-Oct 68 7.74 2339.00 2.59 134.11 19.89 35.73 55.62 30.97

25-Oct 70 7.74 2523.00 2.71 111.67 16.65 33.18 49.83 31.26

26-Oct 71 7.72 2408.00 2.67 80.44 22.06 33.70 55.75 36.96

27-Oct 72 7.57 2370.00 2.15

28-Oct 73 7.64 2372.00 2.98 88.33 18.53 31.97 50.50 35.24

29-Oct 74 7.59 2410.00 1.34 109.31 15.46 27.16 42.62 31.11

30-Oct 75 7.81 2340.00 2.69 99.89 16.19 28.01 44.20 30.34

31-Oct 76 8.10 2447.00 4.25 107.10 8.95 20.22 29.17 19.22

1-Nov 77 7.84 2449.00 3.11 128.79 10.42 26.21 36.63 22.24

2-Nov 78 7.94 2426.00 3.91 142.66 11.80 26.56 38.36

3-Nov 79 7.82 2347.00 3.45 146.11 12.51 25.64 38.16 21.26

4-Nov 80 7.88 2490.00 4.14 122.33 15.10 27.38 42.48 28.60

8-Nov 84 7.78 2346.00 3.38 100.30 20.56 24.70 45.25 31.47

9-Nov 85 7.90 2460.00 7.46 136.68 17.48 26.14

10-Nov 86 7.74 2272.00 3.52 97.03 19.77 24.26

11-Nov 87 7.82 2430.00 3.14 129.20 5.60 6.73

Average 7.80 2383.14 3.46 116.12 14.90 28.59 42.52 28.58

Std.Dev. 0.13 77.27 1.20 19.55 4.35 5.93 7.21 5.30

101


12-Nov 88 7.89 2207.00 6.05 163.00 0.76 0.12 0.88 13-Nov 89 7.83 2196.00 7.64 155.97 0.91 0.18 1.09 15-Nov 91 7.90 2262.00 6.72 156.60 2.28 0.12 2.40 16-Nov 92 7.85 2223.00 7.05 152.75 0.79 0.17 0.96 17-Nov 93 7.87 2229.00 7.08 166.48 3.55 0.16 3.70 18-Nov 94 7.89 2302.00 7.57 150.27 2.99 0.16 3.15 19-Nov 95 7.91 2254.00 6.66 143.06 0.90 0.12 1.02 20-Nov 96 7.88 2223.00 5.91 155.92 1.62 2.42 4.04 22-Nov 98 7.86 2185.00 7.81 143.64 0.67 0.08 0.75 23-Nov 99 7.84 2095.00 6.06 136.85 1.06 0.11 1.17 29-Nov 105 7.81 2256.00 5.99 122.65 1.87 0.23 2.10 30-Nov 106 7.77 2330.00 5.92 158.60 1.97 0.13 2.10 1-Dec 107 7.70 2186.00 6.51 125.79 3.46 0.15 3.61 2-Dec 108 7.83 2236.00 5.81 139.67 2.81 0.23 3.04 3-Dec 109 7.85 2242.00 6.34 163.30 5.52 1.69 7.21 6-Dec 112 7.84 2156.00 5.92 155.22 2.72 2.72 7-Dec 113 7.77 2056.00 5.86 146.59 1.55 1.47 3.02 8-Dec 114 7.83 2148.00 6.02 160.07 2.19 0.68 2.87

Average 7.84 2210.33 6.50 149.80 2.12 0.40 2.50 Std.Dev. 0.05 67.36 0.67 12.50 1.27 0.69 1.58

102



12-Nov 88 7.80 2046.00 3.28 129.20 19.42 28.39 47.81 31.06

13-Nov 89 7.93 2064.00 1.33 113.20 4.52 42.90 47.42 32.19

15-Nov 91 7.80 2076.00 1.33 103.65 8.92 47.21 56.13 37.95

16-Nov 92 7.72 2033.00 1.65 100.15 13.40 49.56 62.95 43.64

17-Nov 93 7.81 1996.00 1.30 86.77 17.99 50.24 68.23 43.39

18-Nov 94 7.72 1993.00 1.42 91.51 14.58 45.91 60.49 42.62

19-Nov 95 7.70 2048.00 4.86 100.97 18.30 49.72 68.02 50.34

20-Nov 96 7.68 2021.00 2.11 88.56 15.25 48.03 63.28 42.97

22-Nov 98 7.38 2024.00 2.74 94.56 19.36 48.98 68.34 50.38

23-Nov 99 7.62 1988.00 3.49 87.55 14.38 51.29 65.68 50.81

29-Nov 105 7.39 1874.00 2.49 73.04 16.62 40.41 57.02 49.23

30-Nov 106 7.58 2013.00 3.28 82.88 17.13 44.96 62.09 41.45

1-Dec 107 7.67 2099.00 1.83 86.82 18.46 47.04 65.51 55.14

2-Dec 108 7.63 1996.00 1.17 94.43 16.61 44.60 61.21 46.40

3-Dec 109 7.58 2004.00 1.62 72.53 17.80 47.66 65.46 42.44

6-Dec 112 7.48 2021.00 2.01 86.48 18.45 50.10 68.54 46.76

7-Dec 113 7.54 1926.00 1.93 72.53 19.34 46.83 66.16 47.79

8-Dec 114 7.84 1911.00 1.87 84.60 8.93 36.91 45.84 30.33

Average 7.66 2007.39 2.21 91.64 15.70 46.06 61.76 44.17

Std.Dev. 26.00 0.15 57.06 0.98 14.34 4.20 5.65 7.43 7.06

103


9-Dec 115 7.85 2262.00 6.28 138.45 4.35 1.90 6.24 10-Dec 116 7.85 2179.00 3.13 155.90 4.51 1.72 6.23 13-Dec 119 7.81 2230.00 7.64 136.63 1.42 1.99 3.40 14-Dec 120 7.85 2258.00 5.90 122.41 2.94 0.12 3.06 15-Dec 121 7.88 2215.00 6.06 124.61 2.12 2.12 16-Dec 122 7.82 2150.00 6.29 98.53 1.69 0.07 1.76 17-Dec 123 7.82 2206.00 5.53 109.77 3.44 1.59 5.02 20-Dec 126 7.89 2298.00 7.40 113.44 3.07 1.98 5.06 21-Dec 127 7.85 2237.00 6.22 115.05 2.51 2.46 4.97 22-Dec 128 7.80 2219.00 5.95 109.25 1.54 0.09 1.63 23-Dec 129 7.80 2285.00 5.61 120.01 25-Dec 131 7.85 2324.00 148.26 0.11 0.11 27-Dec 133 7.84 2287.00 8.66 165.86 2.15 5.07 7.22 28-Dec 134 7.86 2234.00 5.64 150.66 2.13 2.26 4.39 29-Dec 135 7.87 2246.00 6.65 144.74 2.38 5.16 7.54 30-Dec 136 7.91 2201.00 6.53 161.28 31-Dec 137 7.79 2248.00 171.95 2.15 2.20 4.35 1-Jan 138 7.86 2412.00 3-Jan 140 7.89 2164.00 6.99 158.71 0.90 0.15 1.05 4-Jan 141 7.91 2138.00 6.91 153.71 2.14 4.23 6.37 5-Jan 142 7.88 2294.00 6.78 157.45 1.88 0.17 2.05

Average 7.85 2242.24 6.34 137.83 2.43 1.84 4.03 Std.Dev. 0.04 63.18 1.13 22.02 0.97 1.69 2.23

104

Table A10. Test point 5. Effluent Concentrations (mg/L) Date Day pH TDS DO NH3-N NO2-N NO3-N NOx-N Nitrification

9-Dec 115 7.73 1956.00 1.26 84.60 10.37 43.85 54.21 41.46 10-Dec 116 7.79 2038.00 2.17 92.38 12.81 45.57 58.38 39.65 13-Dec 119 7.64 2023.00 1.99 78.16 13.15 48.14 61.28 47.49 14-Dec 120 7.66 2002.00 1.72 75.13 14.52 49.42 63.94 55.31 15-Dec 121 7.70 2046.00 1.37 80.13 14.07 49.98 64.05 54.42 16-Dec 122 7.63 2000.00 3.02 71.59 13.31 49.55 62.86 67.55 17-Dec 123 7.53 1929.00 1.03 51.04 13.47 48.27 61.74 59.55 20-Dec 126 7.66 2028.00 5.47 53.25 20.28 57.21 77.49 72.32 21-Dec 127 7.77 2077.00 2.50 66.72 12.74 53.73 66.46 61.16 22-Dec 128 7.71 2050.00 1.35 65.17 12.50 51.31 63.81 61.84 23-Dec 129 7.79 2000.00 1.80 72.94 25-Dec 131 7.56 2063.00 87.02 16.54 64.72 81.26 58.03 27-Dec 133 7.56 2090.00 4.56 95.80 15.17 61.74 76.90 49.09 28-Dec 134 7.46 2046.00 1.58 82.60 11.30 60.53 71.83 50.48 29-Dec 135 7.74 1964.00 1.12 74.73 11.84 61.32 73.16 53.52 30-Dec 136 7.66 2005.00 2.07 86.67 31-Dec 137 7.65 1948.00 77.78 21.12 49.86 70.98 43.71 1-Jan 138 7.65 1986.00 3-Jan 140 7.76 1976.00 4.79 93.90 15.10 45.51 60.62 40.44 4-Jan 141 7.73 1947.00 2.89 74.43 11.40 44.85 56.25 38.75 5-Jan 142 7.71 1922.00 2.67 88.42 11.07 46.65 57.72 38.82

Average 7.67 2004.57 2.41 77.62 13.93 51.79 65.72 51.87 Std.Dev. 0.09 48.85 1.31 12.22 2.94 6.53 7.84 10.27

105

Table A11. Test point 6. Influent Concentrations (mg/L) Date Day pH TDS DO NH3-N NO2-N NO3-N NOx-N 6-Jan 143 7.73 6.94 14.33 9.62 23.95 7-Jan 144 7.84 6.64 8-Jan 145 7.88 2308.00 6.92 151.26 1.08 3.89 4.97

10-Jan 147 7.86 2117.00 6.30 145.90 1.92 10.27 12.19 11-Jan 148 7.83 2313.00 7.77 156.37 0.85 8.16 9.01 12-Jan 149 7.81 2127.00 6.69 149.11 2.74 2.74 13-Jan 150 7.88 2107.00 6.89 185.51 14-Jan 151 7.87 2154.00 6.73 168.69 2.37 5.01 7.38 15-Jan 152 7.86 2166.00 7.25 153.39 1.63 1.94 3.57 16-Jan 153 7.88 2206.00 7.47 146.86 1.13 1.67 2.80 17-Jan 154 7.90 2260.00 168.02 1.26 3.74 5.00 18-Jan 155 7.87 2240.00 130.47 0.94 5.43 6.38 19-Jan 156 7.87 2262.00 119.70 1.37 5.57 6.93 20-Jan 157 7.83 2227.00 129.29 21-Jan 158 7.86 2242.00 131.93 1.46 2.57 4.03 22-Jan 159 7.89 2168.00 117.77 24-Jan 161 7.87 2016.00 4.95 157.44 0.66 4.34 5.00 25-Jan 162 7.88 2223.00 6.09 151.86 5.46 5.46 26-Jan 163 7.85 2087.00 5.98 140.17 1.31 3.84 5.15 27-Jan 164 7.86 1908.00 5.97 146.94 1.76 3.18 4.93 28-Jan 165 7.83 2185.00 5.50 146.94 0.63 5.27 5.90 29-Jan 166 7.87 2135.00 5.81 145.20 0.62 3.17 3.79 31-Jan 168 7.91 2040.00 5.23 124.43 0.24 1.97 2.21 1-Feb 169 7.91 2117.00 5.20 143.85 0.61 5.23 5.84 2-Feb 170 7.88 2137.00 5.96 137.06 2.64 2.64 3-Feb 171 7.78 2160.00 5.16 129.02 0.42 2.33 4-Feb 172 7.79 2057.00 7.00 131.94 0.74 3.02 3.76 6-Feb 174 7.87 2163.00 6.42 122.71 1.20 6.89 8.09 7-Feb 175 7.84 2154.00 6.35 170.34 1.15 6.69 7.84 8-Feb 176 7.87 2030.00 6.11 116.93 0.10 0.10 9-Feb 177 7.85 2302.00 5.00 157.37 0.67 3.60 4.27

11-Feb 179 7.77 2248.00 5.53 164.24 0.92 2.94 3.86 13-Feb 181 7.81 2211.00 6.71 171.02 1.15 4.75 5.90

Average 7.85 2163.55 6.24 158.35 1.64 4.35 5.84 Std.Dev. 0.04 93.20 0.78 17.22 2.75 2.34 4.36

106


Date Day pH TDS DO NH3-N NO2-N NO3-N NOx-N

Nitrification

6-Jan 143 6.49 1949.00 2.33 8.49 92.38 100.87 7-Jan 144 7.64 2.71 8-Jan 145 7.51 1.53 93.90 13.68 128.99 142.67 99.87 10-Jan 147 6.80 2048.00 4.77 65.47 9.89 92.39 102.28 74.23 11-Jan 148 7.45 1862.00 3.83 91.61 3.40 86.83 90.23 61.09 12-Jan 149 7.93 2041.00 7.66 101.95 1.40 83.98 85.38 60.63 13-Jan 150 7.93 1920.00 5.66 93.87 14-Jan 151 7.78 1869.00 6.89 48.26 1.75 140.95 142.70 89.57 15-Jan 152 7.60 1889.00 82.70 1.24 86.86 88.10 60.81 16-Jan 153 7.47 1896.00 7.85 71.71 1.51 84.79 86.30 62.22 17-Jan 154 7.47 1923.00 67.04 2.14 92.07 94.21 59.37 18-Jan 155 7.04 1955.00 53.87 2.76 103.58 106.34 86.30 19-Jan 156 7.28 1938.00 43.14 3.05 95.47 98.52 87.15 20-Jan 157 6.73 1947.00 43.14 2.14 108.71 110.85 90.78 21-Jan 158 6.59 1936.00 52.79 6.17 106.62 112.79 90.52 22-Jan 159 7.24 1953.00 62.08 24-Jan 161 6.87 1906.00 0.88 68.97 5.43 116.60 122.04 82.07 25-Jan 162 6.56 1762.00 5.57 56.68 2.60 102.53 105.13 73.30 26-Jan 163 6.79 1907.00 3.93 64.69 4.42 98.17 102.59 77.50 27-Jan 164 6.49 1824.00 4.80 60.99 2.70 98.24 100.94 72.73 28-Jan 165 6.44 1656.00 4.87 41.37 1.68 101.20 102.89 74.14 29-Jan 166 6.87 1867.00 4.76 64.98 4.26 91.77 96.03 70.03 31-Jan 168 6.29 1858.00 2.79 2.72 100.16 102.88 87.55 1-Feb 169 4.15 1803.00 5.29 51.07 1.41 109.75 111.16 81.82 2-Feb 170 7.02 1822.00 4.93 53.60 1.41 96.18 97.59 75.39 3-Feb 171 7.43 1874.00 4.86 61.85 2.79 60.91 63.69 52.27 4-Feb 172 7.28 1892.00 2.00 97.13 5.78 87.64 93.42 74.97 6-Feb 174 7.23 1808.00 3.46 62.10 6.66 80.62 87.28 75.31 7-Feb 175 7.13 1859.00 3.70 60.59 6.83 88.15 94.98 59.04 8-Feb 176 6.52 1845.00 3.54 74.44 5.60 98.24 103.84 94.03 9-Feb 177 5.63 1775.00 4.17 67.16 2.16 97.04 99.20 66.74 11-Feb 179 6.76 2002.00 3.71 67.34 7.03 75.48 82.51 53.19 13-Feb 181 6.61 1990.00 2.31 99.54 8.17 93.05 101.22 62.67

Average 7.00 1886.04 4.29 79.61 4.31 101.05 100.94 74.74 Std.Dev. 0.73 82.10 1.74 16.61 3.02 15.42 16.00 13.02

107


14-Feb 182 7.82 2131.00 5.28 151.16 0.85 0.68 1.53 15-Feb 183 7.89 2191.00 5.79 160.19 0.90 0.53 1.44 16-Feb 184 7.90 2202.00 5.73 160.19 1.24 0.55 1.78 17-Feb 185 7.89 2275.00 6.76 177.14 1.47 0.83 2.30 18-Feb 186 7.94 2263.00 6.85 155.31 1.55 0.96 2.51 19-Feb 187 7.92 2231.00 6.40 119.25 1.38 0.67 2.05 20-Feb 188 7.91 2270.00 5.00 168.45 1.63 0.81 2.43 21-Feb 189 7.83 2277.00 5.68 104.74 1.28 0.81 2.08 22-Feb 190 7.91 2262.00 6.69 169.20 1.50 0.48 1.99 23-Feb 191 7.84 2350.00 155.07 1.20 0.22 1.42 24-Feb 192 7.86 2227.00 7.35 167.87 1.23 0.55 1.79 25-Feb 193 7.79 2275.00 6.59 176.67 2.17 1.25 3.42 26-Feb 194 7.86 2260.00 6.53 166.25 1.97 0.79 2.77 27-Feb 195 7.88 2255.00 7.29 139.10 1.80 0.69 2.49 28-Feb 196 8.09 2251.00 6.31 151.95 1.51 0.77 2.28 1-Mar 197 7.98 2298.00 6.27 139.03 0.95 0.49 1.44 2-Mar 198 8.00 2327.00 6.70 133.86 2.69 1.03 3.72 3-Mar 199 7.99 2253.00 5.04 135.56 1.13 0.51 1.64 4-Mar 200 7.88 2238.00 5.44 196.41 1.84 1.55 3.39 5-Mar 201 7.93 2278.00 6.32 148.09 0.71 0.05 0.76 6-Mar 202 8.00 2270.00 6.25 152.75 1.14 0.54 1.68 7-Mar 203 7.95 2310.00 6.43 179.69 1.60 1.15 2.75 8-Mar 204 8.45 2212.00 167.61 0.00 0.11 0.11 9-Mar 205 7.89 2318.00 172.21 0.76 0.31 1.06

10-Mar 206 7.78 2260.00 191.17 1.22 0.91 2.12 11-Mar 207 7.89 2254.00 6.58 173.54 1.35 1.36 2.71 12-Mar 208 7.75 2281.00 6.71 171.54 0.00 0.04 0.04 13-Mar 209 7.82 2262.00 5.96 176.93 0.95 0.00 0.95 14-Mar 210 7.96 2301.00 6.04 188.96 2.75 1.19 3.94 15-Mar 211 7.86 2259.00 6.24 151.34 1.49 1.13 2.62 16-Mar 212 17-Mar 213 7.86 2216.00 5.97 144.70 0.00 0.10 0.10 18-Mar 214 7.90 2331.00 6.70 160.46 1.25 0.84 2.09 19-Mar 215 Average 7.91 2258.29 6.24 158.87 1.26 0.66 1.93 Std.Dev. 0.12 47.21 0.58 19.50 0.62 0.39 0.95

108

Table A14. Test point 7. Effluent Concentrations (mg/L) Date Day pH TDS DO NH3-N NO2-N NO3-N NOx-N Nitrification

14-Feb 182 8.31 2063.00 2.70 127.01 6.74 15.15 21.89 15.34 15-Feb 183 8.12 2045.00 6.09 116.20 4.99 14.30 19.29 12.75 16-Feb 184 7.97 2100.00 4.33 138.83 5.89 14.86 20.75 13.71 17-Feb 185 7.96 2114.00 3.91 132.53 6.29 14.20 20.49 12.25 18-Feb 186 7.92 2191.00 3.11 138.83 6.53 14.30 20.84 14.21 19-Feb 187 8.00 2157.00 3.16 113.13 5.60 11.48 17.08 15.17 20-Feb 188 7.94 2140.00 3.01 114.86 8.17 15.63 23.80 14.96 21-Feb 189 7.86 2179.00 3.25 100.58 8.03 13.77 21.80 22.04 22-Feb 190 7.81 2187.00 3.65 126.72 8.98 14.62 23.60 14.77 23-Feb 191 7.81 2162.00 143.84 10.01 16.08 26.09 17.81 24-Feb 192 7.84 2248.00 3.27 113.87 1.96 3.13 5.09 3.21 25-Feb 193 7.86 2126.00 3.12 132.50 11.97 17.32 29.30 17.56 26-Feb 194 7.89 2178.00 4.16 141.15 9.74 14.66 24.40 15.54 27-Feb 195 7.88 2163.00 3.54 125.70 10.87 16.01 26.88 20.46 28-Feb 196 8.02 2155.00 3.66 148.89 9.65 13.85 23.50 16.38 1-Mar 197 7.87 2180.00 3.78 109.81 5.52 12.26 17.78 13.54 2-Mar 198 8.03 2221.00 3.75 109.81 8.16 13.53 21.69 17.16 3-Mar 199 7.97 2234.00 3.34 108.89 6.31 13.48 19.79 15.46 4-Mar 200 7.87 2169.00 3.32 152.75 10.34 15.42 25.76 13.89 5-Mar 201 7.95 2148.00 3.65 136.54 9.95 12.41 22.36 15.99 6-Mar 202 7.87 2182.00 3.20 149.24 11.24 13.36 24.60 17.05 7-Mar 203 7.95 2185.00 3.57 158.16 8.53 12.94 21.47 12.65 8-Mar 204 7.70 2181.00 165.03 11.83 14.60 26.43 16.69 9-Mar 205 7.92 2154.00 148.09 9.88 13.88 23.76 14.61

10-Mar 206 7.70 2233.00 136.01 10.92 13.78 24.69 13.68 11-Mar 207 7.81 2188.00 3.96 150.98 8.41 13.32 21.73 13.26 12-Mar 208 7.68 2167.00 3.46 168.91 9.83 13.51 23.34 14.41 13-Mar 209 7.80 2182.00 3.67 157.55 16.95 16.47 33.42 20.00 14-Mar 210 7.88 2165.00 3.45 160.00 13.65 16.60 30.26 16.95 15-Mar 211 7.96 2197.00 3.86 149.50 10.93 17.19 28.12 19.68 16-Mar 212 17-Mar 213 7.92 2180.00 3.47 141.78 13.16 17.67 30.83 22.56 18-Mar 214 7.97 2120.00 4.01 150.95 12.61 15.78 28.39 18.73 Average 7.91 2162.44 3.61 137.51 9.17 14.43 23.60 15.89 Std.Dev. 0.12 45.17 0.61 17.88 2.87 2.51 4.89 3.42

109

Table A15. Average Values

Flow Rate (mL/min)

HRT (min)

HRT (days)

Av. Initial TDS

(mg/L)

Av. Final TDS

(mg/L)

Av. Initial NH4-N (mg/L)

Av. Final

NH4-N (mg/L)

Av. Initial NOx-N (mg/L)

Av. Final

NOx-N (mg/L)

0.3 210 0.15 2153.800 1886.000 167.660 84.293 6.880 104.990

0.5 126 0.09 2263.600 1929.800 144.832 68.612 2.370 87.340

0.6 105 0.07 2242.200 2004.600 145.938 82.186 4.030 65.720

0.7 90 0.06 2210.000 2007.400 158.612 97.025 2.490 61.760

1 63 0.04 2261.000 1994.900 169.899 118.578 3.220 62.26

1.5 42 0.029 2563.500 2383.140 174.727 122.940 2.930 42.520

1.7 37 0.026 2258.290 2162.441 168.216 145.601 1.925 23.600

Table A15. Continued

Flow Rate (mL/min)

HRT (min)

HRT (days)

Av. Initial pH

Av. Final pH

Av. Initial DO

Av. Final DO

Nitrification Efficiency

%

0.3 210 0.15 7.85 7 6.3 4.29 74.74

0.5 126 0.09 7.88 7.01 6.01 4.13 68.87

0.6 105 0.07 7.85 7.67 6.34 2.4 51.87

0.7 90 0.06 7.84 7.66 6.49 2.21 44.17

1 63 0.04 7.85 7.56 7.2 3.41 39.29

1.5 42 0.029 7.87 7.801 7.08 3.46 28.57

1.7 37 0.026 7.91 7.91 6.24 3.06 15.89

110

Table A16. Continued

Flow Rate (mL/min)

HRT (min)

HRT (days)

Std. Initial pH

Std. Final pH

Std. Initial DO

Std. Final DO

Std. % final Nitrification

0.3 210 0.15 0.03 0.71 0.76 1.81 13.02 0.5 126 0.09 0.15 0.23 1.71 0.65 13.65 0.6 105 0.07 0.03 0.08 1.13 1.31 10.27 0.7 90 0.06 0.05 0.15 0.67 0.67 7.06 1 63 0.04 0.05 0.24 0.61 0.61 10.41

1.5 42 0.029 0.05 0.125 0.91 1.2 5.3 1.7 37 0.026 0.12 0.12 0.58 0.61 3.42

Table A16. Standard Deviation Values Flow Rate

(mL/min) HRT (min)

HRT (days)

Std. Initial TDS

Std. Final TDS

Std. Initial NH4-N

Std. Final NH4-N

Std. Initial NOx-N

Std. Final

NOx-N

0.3 210 0.15 93.197 82.096 17.216 16.606 4.357 16.004

0.5 126 0.09 92.772 81.747 23.879 15.536 1.097 9.325

0.6 105 0.07 63.185 48.846 22.023 12.221 2.235 7.841

0.7 90 0.06 67.355 57.055 12.498 14.345 2.490 7.430

1 63 0.04 98.629 104.600 24.900 19.888 2.238 10.702

1.5 42 0.029 62.811 77.265 16.263 19.552 1.131 7.205

1.7 37 0.026 47.21 45.17 19.50 18.31 0.95 4.88

Tabl

e A

17. V

olum

etric

Con

vers

ion

Rat

es

Flow

Rat

e (m

L/m

in)

HR

T (m

in)

HR

T (d

ays)

Av.

Initi

al

NH

4-N

(mg/

L)

Av.

Fin

al

NO

x-N

(mg/

L)

%

Nitr

ifica

tion

Prod

uced

(N

Ox/N

H4)

Con

vers

ion

Rat

es p

er u

nit

Vol

ume

(gN

OX/L

-day

)

Con

vers

ion

Rat

es p

er

Surf

ace

Are

a (g

NO

x/m2 -d

)

N-L

oadi

ng

Rat

e (g

NH

4/m2 -d

)

N re

mov

al

rate

(g

NH

4/m2 -d

)

0.3

210

0.15

16

7.66

0 10

4.99

0 74

.74

4.94

0.

59

0.94

0.

47

0.5

126

0.09

14

4.83

2 87

.340

68

.87

11.4

1 1.

36

2.26

1.

07

0.6

105

0.07

14

5.93

8 65

.720

51

.87

12.3

6 1.

48

3.28

1.

85

0.7

90

0.06

15

8.61

2 61

.760

44

.17

15.8

1 1.

89

4.85

2.

97

1 63

0.

04

169.

899

62.2

60

39.2

9 32

.53

3.89

10

.61

7.40

1.5

42

0.02

9 17

4.72

7 42

.520

28

.57

49.9

8 5.

97

24.5

4 17

.27

1.7

37

0.02

6 16

8.21

6 23

.600

15

.89

35.6

3 4.

26

30.3

5 26

.27

111

112

Table A18. Mass Calculations

Flow Rate (mL/min)

HRT (min)

HRT (days)

Av. Initial NH4-N

(g)

Av. Final NOx (g)

Av. Effluent NH4-N

(g)

Av Inflluent NOx-N

(g) 0.3 210 0.15 0.072 0.045 0.04 0.0030 0.5 126 0.09 0.104 0.063 0.05 0.0017 0.6 105 0.07 0.126 0.057 0.07 0.0035 0.7 90 0.06 0.160 0.062 0.10 0.0025 1 63 0.04 0.245 0.090 0.17 0.0046

1.5 42 0.03 0.377 0.092 0.27 0.0063 1.7 37 0.026 0.412 0.058 0.36 0.0047

Table A19. Reactor Efficiency using variable surface areas Conversion Rates per Surface Area 900 Membranes (gNOx-N/m2-d)

Conversion Rates per Surface Area 450 Membranes (gNOx-N/m2-d)

Final NOx-N (g)

900 Membranes

% Efficiency

900 Membranes

Final NOx-N (g)

450 Membranes

% Efficiency

450 Membranes

0.34 0.69 0.0454 62.62 0.0227 31.31

0.48 0.95 0.0629 60.30 0.0314 30.15

0.43 0.86 0.0568 45.03 0.0284 22.52

0.47 0.94 0.0623 38.94 0.0311 19.47

0.68 1.36 0.0897 36.65 0.0448 18.32

0.70 1.39 0.0918 24.34 0.0459 12.17

0.44 0.88 0.0578 14.03 0.0289 7.01

113

Table A20. Sample Calculations

Flow Rate

(mL/min)

Conversion Rates per Surface Area 3600 Membranes (gNOx-N/m2-d)

Final NOx-N (g) 3600

Membranes

Efficiency (%) at a constant rate 3600 Membranes

0.3 0.086 0.1814 250.48 0.5 0.119 0.2515 241.22 0.6 0.108 0.2271 180.13 0.7 0.118 0.2490 155.75 1 0.170 0.3586 146.58

1.5 0.174 0.3674 97.34 1.7 0.110 0.2311 56.12

114

APPENDIX B

RAW DATA. SIGMA PLOT GRAPHS

115

HFMDays

0 50 100 150 200Fe

ed p

H

0

2

4

6

8

Effl

uent

pH

0

2

4

6

8

Feed

TD

S (m

g/L)

0

500

1000

1500

2000

2500

3000

Days

0 50 100 150 200

Efflu

ent T

DS

(mg/

L)

0

500

1000

1500

2000

2500

3000

x = 7.01std = 0.23

x = 7.88std = 0.15

x = 2263.6std = 92.77

x = 1929.86std = 81.74

x = 7.86std = 0.05

x = 7.55std = 0.24

x = 2261std = 98.6

x = 1994std = 104.62

x = 7.86std = 0.05

x = 7.8std = 0.12

x = 2563std =62.81

x = 2383std = 77.26

x = 7.845std =0.05

x = 7.65std = 0.15

x = 2210std = 67.35

x = 2007std = 57.05

x = 7.85std = 0.03

x = 2242.2std = 63.18

x = 2004.5std = 48.8

Flow Rate 0.5 mL/min

Flow Rate1.0 mL/min


Flow Rate0.6 mL/min


Flow Rate0.3 mL/min

x = 7.67std = 0.08

x = 7.00std = 0.73

x = 7.85std = 0.04

x = 2163std = 93.19

x = 1886.0std = 82.09

Flow Rate1.7 mL/min

x = 7.90std = 0.07

x =7.94std = 0.12

x = 2255std =49.30

x = 2157std = 54.0

Figure B1. Raw data for pH and TDS

116

HFMDays

0 50 100 150 200

Inf.

DO

(mg/

L)

0

2

4

6

8

10

Effl

. DO

(mg/

L)

0

1

2

3

4

5

6

Inf.

NH

4 (m

g/L)

0

50

100

150

200

250

Days

0 50 100 150 200

Effl

. NH

4 (m

g/L)

020406080100120140160180

x = 4.13std = 0.65

x = 136.78std = 23.87

x = 64.80std = 15.53

x = 7.19std = 0.71

x = 3.41std = 0.61

x = 160.46std = 24.9

x = 111.99std = 19.88

x = 6.00std = 1.71

x = 7.08std = 0.91

x = 3.45std = 1.20

x = 165std = 16.26

x = 116std = 19.5

x = 6.49std = 0.67

x = 2.20std = 0.98

x = 149.8std = 12.49

x = 91.6std = 14.34

x = 6.34std = 1.12

x = 2.41std = 1.31

x = 137.8std = 22.0

x = 77.623std = 12.2


Flow Rate1.0 mL/min


Flow Rate0.6 mL/min


Flow Rate0.3 mL/min

x = 6.24std = 0.77

x = 4.28std = 1.73

x = 158.34std = 17.21

x = 79.71std = 16.6

Flow Rate1.7 mL/min

x = 6.25std = 0.72

x = 3.66std = 0.73

x = 151.59std = 22.14

x = 129.37std = 16.7

Figure B2. Raw data for dissolved oxygen and ammonia

117

HFMDays

0 50 100 150 200In

f. N

Ox

(mg/

L)

0

5

10

15

20

25

30

Days

0 50 100 150 200

Effl.

NO

x (m

g/L)

0

20

40

60

80

100

120

140

160

x =2.37std = 1.1

x = 87.33std = 9.32

x = 3.22std = 2.23

x = 62.26std =10.7

x = 2.93std = 1.13

x = 42.51std = 7.20

x = 2.49std = 1.58

x = 61.76std = 7.43

x = 4.03std = 2.23

x = 65.71std = 7.84


Flow Rate1.0 mL/min


Flow Rate0.6 mL/min


Flow Rate0.3 mL/min

x = 5.84std = 4.35

x = 100.94std = 16.0

Flow Rate1.7 mL/min

x = 2.15std = 0.54

x = 21.65std = 5.53

Figure B3. Raw data for nitrogen oxides

APPENDIX C

MASS TRANSFER CALCULATIONS

118

INIT

IAL

DO

CA

LCU

LATI

ON

S

Flux

Cal

cula

tions

V=

0.06

3 L

Q

= 0.

3 cm

3 /min

Q=

cm

3 /min

Ope

ratin

g Pr

essu

re=

0.5

psi

O

pera

ting

Pres

sure

= 0.

0340

2286

at

m

H

enry

's co

nsta

nt fo

r O2=

41

100

atm

Surf

ace

Are

a pe

r HF=

1.

4645

cm

2

Tota

l Mem

bran

e Su

rfac

e A

rea=

52

72.2

cm

2

CL

(0)=

0.

45

mg-

DO

/L

M

embr

ane

Thic

knes

s=

0.00

8 cm

Mem

bran

e Th

ickn

ess=

0.

0000

8 m

Ta

ble

C1.

Initi

al D

O c

alcu

latio

ns a

t 0.3

mL/

min

Tim

e C

L (ti

me)

C

hang

e in

Con

c C

hang

e in

Ti

me

Flux

(J)

Flux

(J)

Flux

(J)

Cha

nge

in C

onc

ko

[min

] [m

g-D

O/L

] [m

mol

-DO

] [m

in]

[mm

ol-D

O/m

in-c

m2 ]

[mm

ol-D

O/m

in-m

2 ] [m

g-D

O/m

in-

m2 ]

[mg-

DO

/m3 ]

[m/m

in]

0 0.

45

- -

- -

- -

- 10

2.

18

3.41

E-03

1.

00E+

01

6.46

E-08

6.

46E-

04

2.07

E-02

1.

73E+

03

1.19

E-05

20

2.

35

3.35

E-04

1.

00E+

01

6.35

E-09

6.

35E-

05

2.03

E-03

1.

70E+

02

1.19

E-05

25

2.

37

3.94

E-05

5.

00E+

00

1.49

E-09

1.

49E-

05

4.78

E-04

2.

00E+

01

2.39

E-05

35

2.

92

1.08

E-03

1.

00E+

01

2.05

E-08

2.

05E-

04

6.57

E-03

5.

50E+

02

1.19

E-05

55

3.

26

6.69

E-04

2.

00E+

01

6.35

E-09

6.

35E-

05

2.03

E-03

3.

40E+

02

5.97

E-06

85

3.

78

1.02

E-03

3.

00E+

01

6.47

E-09

6.

47E-

05

2.07

E-03

5.

20E+

02

3.98

E-06

10

0 3.

82

7.88

E-05

1.

50E+

01

9.96

E-10

9.

96E-

06

3.19

E-04

4.

00E+

01

7.97

E-06

14

0 3.

85

5.91

E-05

4.

00E+

01

2.80

E-10

2.

80E-

06

8.96

E-05

3.

00E+

01

2.99

E-06

45

5 3.

89

7.88

E-05

3.

15E+

02

4.74

E-11

4.

74E-

07

1.52

E-05

4.

00E+

01

3.79

E-07

119

Tabl

e C

2. In

itial

DO

cal

cula

tions

at 5

mL/

min

Tim

e C

L (ti

me)

C

hang

e in

Con

c

Cha

nge

in

Tim

e Fl

ux (J

) Fl

ux (J

) Fl

ux (J

) C

hang

e in

C

onc

ko

[min

] [m

g-D

O/L

] [m

mol

-DO

] [m

in]

[mm

ol-D

O/m

in-c

m2 ]

[mm

ol-D

O/m

in-m

2 ] [m

g-D

O/m

in-m

2 ] [m

g-D

O/m

3 ] [m

/min

] 0

0.67

-

- -

- -

- -

5 2.

52

3.64

E-03

5

1.38

E-07

1.

38E-

03

4.42

E-02

18

50

2.39

E-05

10

2.

66

2.76

E-04

5

1.05

E-08

1.

05E-

04

3.35

E-03

14

0 2.

39E-

05

15

2.79

2.

56E-

04

5 9.

71E-

09

9.71

E-05

3.

11E-

03

130

2.39

E-05

30

2.

85

1.18

E-04

15

1.

49E-

09

1.49

E-05

4.

78E-

04

60

7.97

E-06

55

2.

86

1.97

E-05

25

1.

49E-

10

1.49

E-06

4.

78E-

05

10

4.78

E-06

65

2.

89

5.91

E-05

10

1.

12E-

09

1.12

E-05

3.

58E-

04

30

1.19

E-05

15

0 2.

89

0.00

E+00

85

0.

00E+

00

0.00

E+00

0.

00E+

00

0 #D

IV/0

! 17

0 2.

89

0.00

E+00

20

0.

00E+

00

0.00

E+00

0.

00E+

00

0 #D

IV/0

!

120

Tabl

e C

3. In

itial

DO

cal

cula

tions

at 1

0 m

L/m

in

Tim

e C

L (ti

me)

C

hang

e in

Con

c

Cha

nge

in

Tim

e Fl

ux (J

) Fl

ux (J

) Fl

ux (J

) C

hang

e in

C

onc

ko

[min

] [m

g-D

O/L

] [m

mol

-DO

] [m

in]

[mm

ol-D

O/m

in-

cm2 ]

[mm

ol-D

O/m

in-

m2 ]

[mg-

DO

/min

-m2 ]

[mg-

DO

/m3 ]

[m/m

in]

0 0.

45

- -

- -

- -

-

10

2.53

4.

10E-

03

10

7.77

E-08

7.

77E-

04

2.49

E-02

20

80

1.19

E-05

15

2.56

5.

91E-

05

5 2.

24E-

09

2.24

E-05

7.

17E-

04

30

2.39

E-05

30

2.58

3.

94E-

05

15

4.98

E-10

4.

98E-

06

1.59

E-04

20

7.

97E-

06

40

2.6

3.94

E-05

10

7.

47E-

10

7.47

E-06

2.

39E-

04

20

1.19

E-05

55

2.65

9.

84E-

05

15

1.24

E-09

1.

24E-

05

3.98

E-04

50

7.

97E-

06

70

2.66

1.

97E-

05

15

2.49

E-10

2.

49E-

06

7.97

E-05

10

7.

97E-

06

100

2.66

0.

00E+

00

30

0.00

E+00

0.

00E+

00

0.00

E+00

0

#DIV

/0!

145

2.66

0.

00E+

00

45

0.00

E+00

0.

00E+

00

0.00

E+00

0

#DIV

/0!

160

2.67

1.

97E-

05

15

2.49

E-10

2.

49E-

06

7.97

E-05

10

7.

97E-

06

121

Ta

ble

C4.

Initi

al D

O c

alcu

latio

ns a

t 21

mL/

min

Tim

e C

L (ti

me)

C

hang

e in

Con

c

Cha

nge

in

Tim

e Fl

ux (J

) Fl

ux (J

) Fl

ux (J

) C

hang

e in

Con

c ko

[min

] [m

g-D

O/L

] [m

mol

-DO

] [m

in]

[mm

ol-D

O/m

in-c

m2 ]

[mm

ol-D

O/m

in-m

2 ] [m

g-D

O/m

in-m

2 ] [m

g-D

O/m

3 ] [m

/min

] 0

0.9

- -

- -

- -

- 8

3.05

4.

23E-

03

8 1.

00E-

07

1.00

E-03

3.

21E-

02

2150

1.

49E-

05

10

3.07

3.

94E-

05

2 3.

73E-

09

3.73

E-05

1.

19E-

03

20

5.97

E-05

13

3.

08

1.97

E-05

3

1.24

E-09

1.

24E-

05

3.98

E-04

10

3.

98E-

05

14

3.18

1.

97E-

04

1 3.

73E-

08

3.73

E-04

1.

19E-

02

100

1.19

E-04

18

3.

21

5.91

E-05

4

2.80

E-09

2.

80E-

05

8.96

E-04

30

2.

99E-

05

28

3.3

1.77

E-04

10

3.

36E-

09

3.36

E-05

1.

08E-

03

90

1.19

E-05

48

2.

84

-9.0

6E-0

4 20

-8

.59E

-09

-8.5

9E-0

5 -2

.75E

-03

-460

5.

97E-

06

58

2.76

-1

.58E

-04

10

-2.9

9E-0

9 -2

.99E

-05

-9.5

6E-0

4 -8

0 1.

19E-

05

68

2.31

-8

.86E

-04

10

-1.6

8E-0

8 -1

.68E

-04

-5.3

8E-0

3 -4

50

1.19

E-05

73

2.

31

0.00

E+00

5

0.00

E+00

0.

00E+

00

0.00

E+00

0

#DIV

/0!

113

2.36

9.

84E-

05

40

4.67

E-10

4.

67E-

06

1.49

E-04

50

2.

99E-

06

122

Tabl

e C

5. In

itial

DO

cal

cula

tions

. Sum

mar

y ta

ble

Flow

rate

A

ir Pr

essu

re

Max

imum

Flu

x ko

(ove

rall)

1/

ko (o

vera

ll)

1/kL

(liq

uid)

Sh

D

iffus

ion

[mL/

min

] [p

si]

[mm

ol-D

O/m

2 -min

] [m

/min

] [m

in/m

] [m

in/m

] [-

] [m

2 /min

]

0.3

0.5

0.00

0646

018

1.19

E-05

83

685.

71

8368

5.71

20

1.

18E-

07

5 0.

5 1.

1202

6E-0

5 1.

1949

5E-0

5 83

685.

71

8368

5.71

20

1.

18E-

07

10

0.5

0.00

0776

716

1.19

495E

-05

8368

5.71

83

685.

71

20

1.18

E-07

21

0.5

0.00

1003

569

1.49

368E

-05

6694

8.57

66

948.

57

25

1.18

E-07

123

FIN

AL

DO

CA

LCU

LATI

ON

S

Fl

ux C

alcu

latio

ns

V=

0.06

3 L

Q=

0.3

cm3 /m

in

Q=

cm

3 /min

O

pera

ting

Pres

sure

= 0.

5 ps

i O

pera

ting

Pres

sure

= 0.

0340

2286

at

m

Hen

ry's

cons

tant

for O

2=

4110

0 at

m

Surf

ace

Are

a pe

r HF=

1.

4645

cm

2 To

tal M

embr

ane

Surf

ace

Are

a=

5272

.2

cm2

CL

(0)=

0

mg-

DO

/L

Mem

bran

e Th

ickn

ess=

0.

008

cm

Mem

bran

e Th

ickn

ess=

0.

0000

8 m

Tabl

e C

6. F

inal

DO

cal

cula

tions

at 0

.3 m

L/m

in

Tim

e C

L (ti

me)

C

hang

e in

Con

c.

Cha

nge

in T

ime

Flux

(J)

Flux

(J)

Flux

(J)

Cha

nge

in C

onc.

ko

[m

in]

[mg-

DO

/L]

[mm

ol-D

O]

[min

] [m

mol

-DO

/min

-cm

2 ] [m

mol

-DO

/min

-m2 ]

[mg-

DO

/min

-m2 ]

[mg-

DO

/m3 ]

[m/m

in]

0 0

- -

- -

- -

- 15

1.

12

2.21

E-03

15

2.

79E-

08

2.79

E-04

8.

92E-

03

1120

7.

97E-

06

50

0.56

-1

.10E

-03

35

-5.9

7E-0

9 -5

.97E

-05

-1.9

1E-0

3 -5

60

3.41

E-06

70

0.

76

3.94

E-04

20

3.

73E-

09

3.73

E-05

1.

19E-

03

200

5.97

E-06

10

5 2.

3 3.

03E-

03

35

1.64

E-08

1.

64E-

04

5.26

E-03

15

40

3.41

E-06

14

0 1.

25

-2.0

7E-0

3 35

-1

.12E

-08

-1.1

2E-0

4 -3

.58E

-03

-105

0 3.

41E-

06

190

2.33

2.

13E-

03

50

8.07

E-09

8.

07E-

05

2.58

E-03

10

80

2.39

E-06

26

5 2.

48

2.95

E-04

75

7.

47E-

10

7.47

E-06

2.

39E-

04

150

1.59

E-06

28

0 2.

6 2.

36E-

04

15

2.99

E-09

2.

99E-

05

9.56

E-04

12

0 7.

97E-

06

124

Ta

ble

C7.

Fin

al D

O c

alcu

latio

ns a

t 1 m

L/m

in

Tim

e C

L (ti

me)

C

hang

e in

C

onc.

C

hang

e in

Tim

e Fl

ux (J

) Fl

ux (J

) Fl

ux (J

) C

hang

e in

Con

c.

ko

[min

] [m

g-D

O/L

] [m

mol

-DO

] [m

in]

[mm

ol-D

O/m

in-

cm2 ]

[mm

ol-D

O/m

in-m

2 ] [m

g-D

O/m

in-

m2 ]

[mg-

DO

/m3 ]

[m/m

in]

0 0.

5 -

- -

- -

- -

15

2.63

4.

19E-

03

15

5.30

E-08

5.

30E-

04

1.70

E-02

21

30

7.97

E-06

20

3.

16

1.04

E-03

5

3.96

E-08

3.

96E-

04

1.27

E-02

53

0 2.

39E-

05

25

2.75

-8

.07E

-04

5 -3

.06E

-08

-3.0

6E-0

4 -9

.80E

-03

-410

2.

39E-

05

40

2.78

5.

91E-

05

15

7.47

E-10

7.

47E-

06

2.39

E-04

30

7.

97E-

06

45

2.61

-3

.35E

-04

5 -1

.27E

-08

-1.2

7E-0

4 -4

.06E

-03

-170

2.

39E-

05

50

2.64

5.

91E-

05

5 2.

24E-

09

2.24

E-05

7.

17E-

04

30

2.39

E-05

60

2.

85

4.13

E-04

10

7.

84E-

09

7.84

E-05

2.

51E-

03

210

1.19

E-05

75

3.

16

6.10

E-04

15

7.

72E-

09

7.72

E-05

2.

47E-

03

310

7.97

E-06

85

3.

17

1.97

E-05

10

3.

73E-

10

3.73

E-06

1.

19E-

04

10

1.19

E-05

10

0 3.

23

1.18

E-04

15

1.

49E-

09

1.49

E-05

4.

78E-

04

60

7.97

E-06

11

0 3.

26

5.91

E-05

10

1.

12E-

09

1.12

E-05

3.

58E-

04

30

1.19

E-05

13

0 3.

29

5.91

E-05

20

5.

60E-

10

5.60

E-06

1.

79E-

04

30

5.97

E-06

13

5 3.

32

5.91

E-05

5

2.24

E-09

2.

24E-

05

7.17

E-04

30

2.

39E-

05

140

3.33

1.

97E-

05

5 7.

47E-

10

7.47

E-06

2.

39E-

04

10

2.39

E-05

15

0 3.

36

5.91

E-05

10

1.

12E-

09

1.12

E-05

3.

58E-

04

30

1.19

E-05

17

0 3.

38

3.94

E-05

20

3.

73E-

10

3.73

E-06

1.

19E-

04

20

5.97

E-06

20

0 3.

41

5.91

E-05

30

3.

73E-

10

3.73

E-06

1.

19E-

04

30

3.98

E-06

21

5 3.

52

2.17

E-04

15

2.

74E-

09

2.74

E-05

8.

76E-

04

110

7.97

E-06

26

0 3.

53

1.97

E-05

45

8.

30E-

11

8.30

E-07

2.

66E-

05

10

2.66

E-06

125

Ta

ble

C8.

Fin

al D

O c

alcu

latio

ns a

t 10

mL/

min

Tim

e C

L (ti

me)

C

hang

e in

C

onc.

C

hang

e in

Tim

e Fl

ux (J

) Fl

ux (J

) Fl

ux (J

) C

hang

e in

Con

c.

ko

[min

] [m

g-D

O/L

] [m

mol

-DO

] [m

in]

[mm

ol-D

O/m

in-c

m2 ]

[mm

ol-D

O/m

in-m

2 ] [m

g-D

O/m

in-

m2 ]

[mg-

DO

/m3 ]

[m/m

in]

0 0

- -

- -

- -

- 5

3.26

6.

42E-

03

5 2.

43E-

07

2.43

E-03

7.

79E-

02

3260

2.

39E-

05

10

2.8

-9.0

6E-0

4 5

-3.4

4E-0

8 -3

.44E

-04

-1.1

0E-0

2 -4

60

2.39

E-05

15

3.

51

1.40

E-03

5

5.30

E-08

5.

30E-

04

1.70

E-02

71

0 2.

39E-

05

20

3.77

5.

12E-

04

5 1.

94E-

08

1.94

E-04

6.

21E-

03

260

2.39

E-05

25

3.

04

-1.4

4E-0

3 5

-5.4

5E-0

8 -5

.45E

-04

-1.7

4E-0

2 -7

30

2.39

E-05

30

3

-7.8

8E-0

5 5

-2.9

9E-0

9 -2

.99E

-05

-9.5

6E-0

4 -4

0 2.

39E-

05

35

2.9

-1.9

7E-0

4 5

-7.4

7E-0

9 -7

.47E

-05

-2.3

9E-0

3 -1

00

2.39

E-05

40

4.

02

2.21

E-03

5

8.36

E-08

8.

36E-

04

2.68

E-02

11

20

2.39

E-05

45

4.

31

5.71

E-04

5

2.17

E-08

2.

17E-

04

6.93

E-03

29

0 2.

39E-

05

50

3.8

-1.0

0E-0

3 5

-3.8

1E-0

8 -3

.81E

-04

-1.2

2E-0

2 -5

10

2.39

E-05

55

3.

79

-1.9

7E-0

5 5

-7.4

7E-1

0 -7

.47E

-06

-2.3

9E-0

4 -1

0 2.

39E-

05

60

3.69

-1

.97E

-04

5 -7

.47E

-09

-7.4

7E-0

5 -2

.39E

-03

-100

2.

39E-

05

65

3.63

-1

.18E

-04

5 -4

.48E

-09

-4.4

8E-0

5 -1

.43E

-03

-60

2.39

E-05

70

3.

44

-3.7

4E-0

4 5

-1.4

2E-0

8 -1

.42E

-04

-4.5

4E-0

3 -1

90

2.39

E-05

75

3.

4 -7

.88E

-05

5 -2

.99E

-09

-2.9

9E-0

5 -9

.56E

-04

-40

2.39

E-05

85

3.

51

2.17

E-04

10

4.

11E-

09

4.11

E-05

1.

31E-

03

110

1.19

E-05

95

3.

55

7.88

E-05

10

1.

49E-

09

1.49

E-05

4.

78E-

04

40

1.19

E-05

126

Tabl

e C

9. F

inal

DO

cal

cula

tions

. Sum

mar

y ta

ble

Flow

rate

A

ir Pr

essu

re

Max

imum

Flu

x ko

(ove

rall)

1/

ko (o

vera

ll)

1/kL

(liq

uid)

Sh

D

iffus

ion

[m

L/m

in]

[psi

] [m

mol

-DO

/m2 -m

in]

[m/m

in]

[min

/m]

[min

/m]

[-]

[m2 /m

in]

0.3

0.5

0.00

0278

821

7.96

631E

-06

1255

28.5

7 12

5528

.57

13

1.18

2E-0

7 1

0.5

0.00

0530

258

7.96

631E

-06

1255

28.5

7 12

5528

.57

13

1.18

2E-0

7 10

0.

5 0.

0001

9417

9 2.

3898

9E-0

5 41

842.

86

4184

2.86

40

1.

182E

-07

C

alcu

latin

g th

e am

ount

of o

xyge

n re

quire

d by

bio

film

at d

iffer

ent f

low

rate

s

NH

4 +1.

863O

2 + 0

.098

CO

2 → 0

.019

6 C

5H7N

O2 +

0.9

8 N

O3 +

0.0

941H

2O +

1.9

8 H

2O

Tota

l Mem

bran

e Su

rfac

e A

rea=

52

72.2

cm

2

O

xyge

n co

nsum

ed p

er a

mm

onia

use

d is

=

4.25

g

O2

Tabl

e C

10. B

iofil

m C

onsu

mpt

ion

Flow

rate

(m

L/m

in)

HR

T

(min

)

NH

4-N

co

nsum

ed

(g)

Bio

film

Oxy

gen

cons

umpt

ion

(m

mol

-DO

/sec

-m2 )

0.3

210

0.03

60

7.20

E-04

0.

5 12

6 0.

0549

1.

83E-

03

0.6

105

0.05

51

2.20

E-03

0.

7 90

0.

0621

2.

90E-

03

1 63

0.

0739

4.

93E-

03

1.5

42

0.11

19

1.12

E-02

1.

7 37

0.

0554

6.

27E-

03

127

APPENDIX D

TRACER STUDY CALCULATIONS

128

Tabl

e D

1. In

itial

trac

er a

t 0.3

mL/

min

time

t/T

(C/C

o)ex

p Pa

rt A

Pa

rt B

th

eore

tical

Co

sum

sq.e

rror

su

m

0 0

0.00

00

0 0

0 0

2.88

100

0.18

0.

0045

0.

252

1.14

4 0.

288

0.08

0

L =

0.2

m

120

0.21

0.

0057

0.

230

1.10

8 0.

255

0.06

2

u =

0.00

0009

m

/s

145

0.26

0.

0102

0.

209

1.07

8 0.

225

0.04

6

D =

0.

0000

1310

m

2 /sec

150

0.27

0.

0102

0.

206

1.07

4 0.

221

0.04

4

d =

7.03

165

0.29

0.

0159

0.

196

1.06

2 0.

208

0.03

7

Pe =

0.

14

175

0.31

0.

0193

0.

190

1.05

5 0.

201

0.03

3

180

0.32

0.

0375

0.

188

1.05

2 0.

197

0.02

6

20

0 0.

36

0.06

59

0.17

8 1.

042

0.18

5 0.

014

220

0.39

0.

1136

0.

170

1.03

4 0.

175

0.00

4

280

0.50

0.

6477

0.

150

1.01

8 0.

153

0.24

5

295

0.53

0.

7523

0.

147

1.01

5 0.

149

0.36

4

325

0.58

0.

7920

0.

140

1.01

1 0.

141

0.42

4

520

0.93

0.

9716

0.

110

1.00

0 0.

110

0.74

2

560

1 0.

9807

0.

106

1.00

0 0.

106

0.76

4

129

Tabl

e D

2. In

itial

trac

er a

t 1 m

L/m

in

time

t/T

(C/C

o)ex

p Pa

rt A

Pa

rt B

th

eore

tical

C

o su

m

sq.e

rror

su

m

0 0.

000

0.00

34

0.00

00

0.00

00

0.00

00

0.00

00

3.38

20

0.06

7 0.

0034

0.

3339

1.

3565

0.

4529

0.

2021

L =

0.2

m

35

0.11

7 0.

0091

0.

2524

1.

1689

0.

2950

0.

0818

u =

0.00

0031

m

/s

50

0.16

7 0.

0159

0.

2112

1.

1021

0.

2327

0.

0470

D =

0.

0000

7 m

2 /sec

60

0.20

0 0.

0466

0.

1928

1.

0775

0.

2077

0.

0260

d =

10.7

1

90

0.30

0 0.

7864

0.

1574

1.

0389

0.

1635

0.

3879

Pe =

0.

09

10

5 0.

350

0.89

77

0.14

57

1.02

86

0.14

99

0.55

93

120

0.40

0 0.

9284

0.

1363

1.

0212

0.

1392

0.

6228

125

0.41

7 0.

9375

0.

1336

1.

0192

0.

1361

0.

6422

300

1 0.

9864

0.

0862

1.

0000

0.

0862

0.

8103

130

Tabl

e D

3. In

itial

trac

er a

t 15

mL/

min

time

t/T

(C/C

o)ex

p Pa

rt A

Pa

rt B

th

eore

tical

C

o su

m

sq.e

rror

su

m

0 0.

000

0.00

0 0.

000

0.00

0 0.

000

0.00

0 3.

780

5 0.

053

0.55

9 0.

375

1.48

7 0.

558

0.00

0

10

0.10

5 0.

645

0.26

5 1.

194

0.31

7 0.

108

L

= 0.

2 m

15

0.15

8 0.

752

0.21

7 1.

110

0.24

1 0.

261

u

= 0.

0004

7 m

/s

20

0.21

1 0.

797

0.18

8 1.

071

0.20

1 0.

355

D

=

0.00

100

m2 /s

ec

25

0.26

3 0.

844

0.16

8 1.

049

0.17

6 0.

446

d

= 10

.74

35

0.36

8 0.

875

0.14

2 1.

026

0.14

5 0.

532

Pe

=

0.09

65

0.68

4 0.

914

0.10

4 1.

003

0.10

4 0.

655

80

0.84

2 0.

921

0.09

4 1.

001

0.09

4 0.

685

95

1.00

0 0.

945

0.08

6 1.

000

0.08

6 0.

738

131

Tabl

e D

4. F

inal

trac

er a

t 0.3

mL/

min

time

t/T

(C/C

o)ex

p Pa

rt A

Pa

rt B

th

eore

tical

Co

sum

sq.e

rror

su

m

0 0

0 0

0 0

0 4.

39

70

0.04

0.

272

0.43

3 1.

723

0.74

7 0.

226

105

0.06

0.

432

0.35

4 1.

416

0.50

1 0.

005

L

= 0.

2 m

140

0.08

0.

456

0.30

6 1.

285

0.39

4 0.

004

u

= 0.

0000

09

m/s

190

0.11

0.

650

0.26

3 1.

189

0.31

3 0.

114

D

=

0.00

0020

m

2 /sec

265

0.15

0.

696

0.22

3 1.

120

0.24

9 0.

199

d

= 10

.85

76

5 0.

43

0.91

9 0.

131

1.01

8 0.

133

0.61

8

Pe =

0.

09

835

0.47

0.

813

0.12

5 1.

014

0.12

7 0.

470

1540

0.

86

0.89

8 0.

092

1.00

1 0.

092

0.64

9

1600

0.

89

0.91

2 0.

091

1.00

0 0.

091

0.67

4

1780

0.

99

0.92

5 0.

086

1.00

0 0.

086

0.70

5

1790

1

0.93

6 0.

086

1.00

0 0.

086

0.72

3

132

Tabl

e D

5. F

inal

trac

er a

t 1 m

L/m

in

time

t/T

(C/C

o)ex

p Pa

rt A

Pa

rt B

th

eore

tical

Co

sum

sq.e

rror

su

m

0 0.

000

0 0

0 0

0 4.

1077

4201

6

15

0.04

5 0.

612

0.33

2 1.

372

0.45

6 0.

024

40

0.11

9 0.

714

0.20

3 1.

106

0.22

5 0.

239

L

= 0.

2 m

45

0.13

4 0.

780

0.19

2 1.

090

0.20

9 0.

326

u

= 0.

0000

31

m/s

75

0.22

4 0.

836

0.14

9 1.

043

0.15

5 0.

464

D

=

0.00

0100

m

2 /sec

11

0 0.

328

0.82

7 0.

123

1.02

2 0.

125

0.49

2

d =

16.1

1

140

0.41

8 0.

865

0.10

9 1.

013

0.11

0 0.

569

Pe

=

0.06

150

0.44

8 0.

903

0.10

5 1.

011

0.10

6 0.

635

200

0.59

7 0.

917

0.09

1 1.

004

0.09

1 0.

681

215

0.64

2 0.

910

0.08

8 1.

003

0.08

8 0.

675

335

1.00

0 0.

931

0.07

0 1.

000

0.07

0 0.

741

133

Tabl

e D

6. F

inal

trac

er a

t 15

mL/

min

time

t/T

(C/C

o)ex

p Pa

rt A

Pa

rt B

th

eore

tical

Co

sum

sq.e

rror

su

m

0

0.00

0 0.

000

0.00

0 0.

000

0.00

0 0.

000

0.26

7934

361

1

0.00

8 0.

174

0.67

9 4.

142

2.81

1 -2

.637

L =

0.2

m

2 0.

017

0.48

2 0.

480

2.01

1 0.

965

-0.4

83

u

= 0.

0004

66

m/s

3 0.

025

0.64

9 0.

392

1.58

0 0.

619

0.02

9

D =

0.

0019

0 m

2 /sec

4

0.03

4 0.

687

0.33

9 1.

401

0.47

5 0.

212

d

= 20

.41

8

0.06

8 0.

774

0.24

0 1.

170

0.28

1 0.

494

Pe

=

0.05

10

0.08

5 0.

814

0.21

5 1.

129

0.24

2 0.

572

13

0.11

0 0.

828

0.18

8 1.

092

0.20

6 0.

622

18

0.15

3 0.

868

0.16

0 1.

059

0.16

9 0.

699

23

0.19

5 0.

908

0.14

1 1.

042

0.14

7 0.

760

28

0.23

7 0.

828

0.12

8 1.

030

0.13

2 0.

696

33

0.28

0 0.

934

0.11

8 1.

023

0.12

1 0.

814

38

0.32

2 0.

946

0.11

0 1.

018

0.11

2 0.

834

53

0.44

9 0.

955

0.09

3 1.

008

0.09

4 0.

861

63

0.53

4 0.

946

0.08

5 1.

005

0.08

6 0.

860

73

0.61

9 0.

971

0.07

9 1.

003

0.08

0 0.

891

88

0.74

6 0.

992

0.07

2 1.

001

0.07

2 0.

920

108

0.91

5 0.

971

0.06

5 1.

000

0.06

5 0.

905

118

1.00

0 0.

980

0.06

2 1.

000

0.06

2 0.

917

134

135

APPENDIX E

T-TEST

Sam

ple

Cal

cula

tions

for T

-test

T-T

est

T*

=[x-

µ]/(S

/(n^0

.5))

W

here

t* is

the

devi

atio

n of

the

estim

ated

mea

n fr

om th

e po

pula

tion

mea

n, m

easu

red

in te

rms o

f the

un

it S/

(n^0

.5)

A lo

w v

alue

of t

* in

dica

tes l

ittle

diff

eren

ce b

etw

een

the

mea

ns

A

hig

h va

lue

of t*

indi

cate

s a la

rge

diff

eren

ce, p

rovi

ding

mor

e ju

stifi

catio

n fo

r rej

ectin

g th

e nu

ll hy

poth

esis

IF

t* >

tc, w

e re

ject

the

null

hypo

thes

is a

nd c

oncl

ude

ther

e is

a

diff

eren

ce

IF

t* <

tc, w

e ca

nnot

reje

ct th

e nu

ll hy

poth

esis

. The

evi

denc

e su

gges

ts th

e sa

mpl

e ha

s not

dev

iate

d fr

om th

e po

pula

tion

Fl

ow

Rat

e H

RT

(day

s)

%

Nitr

ifica

tion

0.3

0.15

74

.74

0.5

0.09

68

.87

0.6

0.07

51

.87

0.7

0.06

44

.17

1 0.

04

39.2

9

1.

5 0.

029

28.5

7

1.

7 0.

026

15.8

9

Mea

n =

46.2

Std.

Dev

iatio

n =

21.0

n =

7

(n-1

) =

6

tc (5

%) =

1.

943

(1 si

de

test

)

tc (1

%) =

3.

143

(1 si

de

test

)

136

13

8

For

the

95%

con

fiden

ce li

mits

t* (

74.7

) =

3.6

t* >

tc in

dica

tes s

tatis

tical

ly si

gnifi

cant

diff

eren

ce, n

ull h

ypot

hesi

s rej

ecte

d t*

( 68

.9) =

2.

9 t*

> tc

indi

cate

s sta

tistic

ally

sign

ifica

nt d

iffer

ence

, nul

l hyp

othe

sis r

ejec

ted

Fo

r th

e 99

% c

onfid

ence

lim

its

t*

( 74

.7) =

3.

6 t*

> tc

indi

cate

s sta

tistic

ally

sign

ifica

nt d

iffer

ence

, nul

l hyp

othe

sis r

ejec

ted

t* (

68.9

) =

2.9

t* <

tc te

st in

dica

tes i

nsuf

ficie

nt e

vide

nce

for a

stat

istic

ally

sign

ifica

nt

diff

eren

ce.

137

PERMISSION TO COPY

In presenting this thesis in partial fulfillment of the requirements for a master’s

degree at Texas Tech University or Texas Tech University Health Sciences Center, I

agree that the Library and my major department shall make it freely available for

research purposes. Permission to copy this thesis for scholarly purposes may be granted

by the Director of the Library or my major professor. It is understood that any copying

or publication of this thesis for financial gain shall not be allowed without my further

written permission and that any user may be liable for copyright infringement.

Agree (Permission is granted.)

Maria Noel Ruiz Careri 03/08/2005 Student Signature Date Disagree (Permission is not granted.) _______________________________________________ ____________ Student Signature Date

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