Tertiary Nitrification Using Membrane Aerated Biofilm Reactors

205 Pages·2013·3.92 MB·English

Tertiary Nitrification Using Membrane Aerated Biofilm Reactors:
Process Optimization, Characterization and Model Development

by

Zebo Long

A Thesis

presented to

The University of Guelph

In partial fulfilment of requirements
for the degree of

Doctor of Philosophy
in
Engineering

Guelph, Ontario, Canada

© Zebo Long, August, 2013
ABSTRACT

Tertiary Nitrification Using Membrane Aerated Biofilm Reactors:
Process Optimization, Characterization and Model Development

Zebo Long Advisor:
University of Guelph, 2013 Professor Hongde Zhou

Membrane aerated biofilm reactor (MABR) process allows higher oxygen transfer efficiencies
than conventionally aerated processes by employing a gas-permeable membrane for oxygen to
diffuse directly into attached biofilm for pollutants oxidation. However, unsolved problems,
such as the difficulties in maintaining an optimum biofilm thickness and lack of scale up rules,
have hampered its engineering.
MABR process for tertiary nitrification holds promise partly because excessive biofilm growth
might be avoided. Previous studies have demonstrated effective nitrification in lab-scale reactors
treating artificial wastewaters. To address the effects of real secondary effluents, two identical
pilot-scale MABRs treating ammonia-supplemented secondary effluent and tap water were
examined under similar operational conditions and optimized at three Reynolds numbers.
Microbial distribution in biofilms under the optimized conditions was then characterized by
fluorescence in-site hybridization (FISH) and confocal laser scanning microscopy (CLSM).
Lastly, a mechanistic oxygen transfer rate (OTR) model was developed and evaluated using a
bench-scale MABR.
Results from pilot studies demonstrated for the first time the feasibility of tertiary nitrification
using MABR to treat secondary effluent. Organic carbon in secondary effluent had facilitated a
quick formation of biofilm. In contrast, artificial wastewater lack of organic carbon required a
reduced mixing to promote initial biomass retention. Equivalent nitrification rates were
eventually achieved under different mixing conditions, suggesting that wastewater sources affect
the optimum operational conditions. The nitrifying biofilms in both reactors were found to have
enhanced the oxygen transfer rates as compared with those of clean membrane modules.
The high ratios of nitrifiers to all bacteria in the biofilms confirmed the potential for high-rate
nitrification in MABRs. Moreover, it was found that four main genera of nitrifiers coexisted
with spatial variations in both reactors. The spatial variations were caused by the oxygen partial
pressure gradient along the hollow fibres that had created variable microenvironments for the
selective growth of nitrifiers.
The proposed mechanistic OTR model accurately predicts OTRs with the measured total mass
transfer coefficients (K ), but underestimates OTRs with the estimated K . The error in
T T
estimating membrane resistance was identified as the cause for the underestimated OTRs. A
“true” membrane resistance is therefore suggested for model calibration.
Dedication

This dissertation is dedicated to:

My wife, Jinqiu Liu, for her endless love and support;

My kids, Xiaoxiao (Michael), Raymond and Rachel, for the joy
and the happiness they bring

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Acknowledgements

I would first like to express my sincere gratitude to my advisor, Dr. Hongde Zhou, for guiding
me through my PhD program with encouragement and patience. His proficiency in water and
wastewater treatment field and critical thinking skills are profound, and I am truly fortunate to
have had the opportunity to learn from him.
I would also like to thank my advisory and examination committee members, Drs. Hermann
Eberl, Khosrow Farahbakhsh, Richard G. Zytner, Sheng Chang, and Steven N. Liss, for their
guidance and support over the years. Their contributions to my intellectual growth are of great
significance.
Special thanks goes to Dr. Lori Lishman, Mr. Peter Seto and Mr. Scott Dunlop for their
consistent support and help during and beyond my pilot study; Mr. Henry Behmann for his
inspiring thoughts and hands-on involvement in making membrane modules; Drs. Holger Daims,
Jack T. Trevors, Mahendran Basuvaraj and Michaela Strüder-Kypke for their valuable
suggestions on carrying out FISH tests, image acquisition and analysis; and many other friends
who have helped me along the way.
Finally, I would like to thank Natural Sciences and Engineering Research Council of Canada and
Wastewater Technology Centre, Environmental Canada (Burlington, Ontario) for providing the
funding that made this research possible, and GE Water & Process Technologies (Oakville) and
ATPwater® Inc. (California) for providing membrane materials and/or membrane modules.
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Table of Contents
DEDICATION.............................................................................................................................. iv
ACKNOWLEDGEMENTS ......................................................................................................... v
TABLE OF CONTENTS ............................................................................................................ vi
LIST OF TABLES ........................................................................................................................ x
LIST OF FIGURES ..................................................................................................................... xi
LIST OF ABBREVIATIONS ................................................................................................... xiii
CHAPTER 1: INTRODUCTION ............................................................................................... 1
1.1 BACKGROUND ........................................................................................................................ 1
1.2 OBJECTIVES ........................................................................................................................... 7
1.3 OUTLINE ................................................................................................................................ 8
REFERENCES .............................................................................................................................. 10
CHAPTER 2: LITERATURE REVIEW ................................................................................ 14
2.1 MEMBRANE USED IN MABR STUDIES .................................................................................. 14
2.1.1 Membrane material and configuration ........................................................................ 14
2.1.3 Membrane operation mode .......................................................................................... 16
2.2 MASS TRANSFER IN MABR .................................................................................................. 17
2.2.1 Membrane gas transport mechanisms ......................................................................... 17
2.2.2 Oxygen mass transfer of clean membrane ................................................................... 18
2.2.3 Mass transfer in biofilm of MABR ............................................................................... 21
2.3 NITROGEN REMOVAL USING MABR .................................................................................... 25
2.3.1 Overview of nitrogen removal processes ..................................................................... 25
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2.3.2 Nitrification using MABR ............................................................................................ 30
2.3.3 Simultaneous removal of organic carbon and Nitrogen in MABR .............................. 38
2.3.4 Nitrogen removal through hybrid MABR .................................................................... 44
2.4 BIOFILM CHARACTERIZATION .............................................................................................. 45
2.4.1 Microsensors for Nutrients’ profiles ............................................................................ 45
2.4.2 CLSM for biofilm structure study ................................................................................ 46
2.4.3 FISH and CLSM combination for microbial community analysis ............................... 48
2.4.4 AFM for biofilm morphology and in situ cohesiveness study ...................................... 49
REFERENCES .............................................................................................................................. 49
CHAPTER 3: PILOT DEMONSTRATION OF MEMBRANE AERATED BIOFILM
REACTORS TO ACHIEVE EQUIVALENT TERTIARY NITRIFICATION IN
SECONDARY EFFLUENT AND ARTIFICIAL WASTEWATER ...................................... 58
3.1 INTRODUCTION..................................................................................................................... 58
3.2 MATERIALS AND METHODS .................................................................................................. 60
3.2.1 Pilot Plant Set-Up and Operation................................................................................ 60
3.2.3 Oxygen supply rate of clean membrane module .......................................................... 68
3.2.4 Analytical Methods ...................................................................................................... 68
3.2.5 Definition of Stable State ............................................................................................. 69
3.3 RESULTS AND DISCUSSION ................................................................................................... 69
3.3.2 Effects of wastewater sources on nitrification performance........................................ 73
3.3.3 Effects of mixing ........................................................................................................... 75
3.3.4 Oxygen utilization rate ................................................................................................. 77
3.3. 5 TN balance and effects of DO in the bulk liquid ......................................................... 80
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3.4 CONCLUSIONS ...................................................................................................................... 81
REFERENCES .............................................................................................................................. 82
CHAPTER 4: MICROBIAL DIVERSITY IN NITRIFYING BIOFILMS OF
MEMBRANE-AERATED BIOFILM REACTORS (MABR) USING FISH AND CLSM
TECHNIQUES ............................................................................................................................ 87
4.1 INTRODUCTION..................................................................................................................... 87
4.2 MATERIALS AND METHODS ................................................................................................. 89
4.2.1 Reactor operation and tests ......................................................................................... 89
4.2.2 Sample collection ......................................................................................................... 90
4.2.3 Sample preparation prior to hybridization .................................................................. 90
4.2.4 Fluorescent in situ hybridization ................................................................................. 91
4.2.5 Image acquisition by CLSM ......................................................................................... 92
4.2.5 Image analysis ............................................................................................................. 95
4.3 RESULTS AND DISCUSSION ................................................................................................... 96
4.3.1 System performance and tests ...................................................................................... 96
4.3.2 Validity of results obtained by FISH ............................................................................ 97
4.3.3 Sample representativeness ......................................................................................... 101
4.3.4 Microbial diversity of nitrifying bacteria and its importance for process stability ... 102
3.5 Spatial distribution of nitrifying bacteria and affecting factors ................................... 105
4.4 CONCLUSIONS .................................................................................................................... 109
REFERENCES ............................................................................................................................ 110
CHAPTER 5: OXYGEN TRANSFER MODEL FOR FLOW-THROUGH HOLLOW
FIBRE MEMBRANE MODULE ............................................................................................ 115
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5.1 INTRODUCTION................................................................................................................... 115
5.2 MODEL FORMULATION ...................................................................................................... 119
5.2.1 Resistance-in-series ................................................................................................... 119
5.2.2 Oxygen transfer rate .................................................................................................. 122
5.2 MATERIALS AND METHODS ................................................................................................ 124
5.2.1 Experimental setup..................................................................................................... 124
5.2.2 Hollow fibre dimension measurement ....................................................................... 126
5.2.3 Tracer study ............................................................................................................... 127
5.2.4 Clean water oxygen transfer tests .............................................................................. 127
5.3 RESULTS AND DISCUSSION ................................................................................................. 129
5.3. 1 Hydrodynamic conditions through trace study ......................................................... 129
5.3.2 Comparison of experimental and model results ........................................................ 130
5.3.3 Estimation of membrane resistance ........................................................................... 134
5.4 CONCLUSIONS .................................................................................................................... 138
REFERENCES ............................................................................................................................ 139
CHAPTER 6: CONCLUSIONS .............................................................................................. 142
APPENDICES ........................................................................................................................... 149
APPENDIX I: PICTURES OF PILOT-SCALE AND BENCH-SCALE REACTORS ................................... 150
APPENDIX II: FISH PROTOCOLS ............................................................................................... 151
APPENDIX III: DATA OF TRACE STUDY ..................................................................................... 168
APPENDIX IV: DATA FOR CLEAN MEMBRANE OXYGEN TRANSFER TESTS ................................. 171
APPENDIX V: MATLAB PROGRAM FOR THE OTR MODEL ......................................................... 177
APPENDIX VI: RAW DATA FOR CHAPTER 3 .............................................................................. 182
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List of Tables
Table 2.1Mass transfer correlations for ducts of various geometries (Basile and Gallucci, 2009)
.............................................................................................................................................. 20
Table 2.2Mass transfer correlations for shell side of hollow fibre modules ................................. 20
Table 2.3 Performance of MABRs for nitrification ...................................................................... 31
Table 2.4 Oxygen supply rates of clean membrane modules in literatures ................................. 34
Table 3.1 Main specifications of MABR pilot plants ................................................................... 61
Table 3.2 Summary of main characteristics of influents (mg/Lexcept NTU for turbidity) .......... 62
Table 3.3 Main experimental conditions for MABR1 .................................................................. 65
Table 3.4 Main experimental conditions for MABR2 .................................................................. 66
Table 3.5 Summary of nitrification efficiency averaged at stable states from MABR1............... 72
Table 3.6 Summary of nitrification efficiency averaged at stable states from MABR2............... 73
Table 4.1 Oligonucleotide probes ................................................................................................. 93
Table 4.2 Concentration of stock solution and working solution of oligonucleotide probes ....... 94
Table 4.3 Average biovolume fraction with standard deviation in biofilm samples of MABR1
treating secondary effluent .................................................................................................... 99
Table 4.4 Average biovolume fraction with standard deviation in biofilm samples of MABR2
treating artificial wastewater ................................................................................................. 99
Table 5.1 Main specifications of bench-scale reactor ................................................................. 126
Table 5.2 Comparison of K , OTR and gas pressure drop obtained from tests and modeling ... 132
T
Table 5.3 Membrane resistance estimated by various methods .................................................. 136

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