system and fouling performances of anaerobic ceramic membrane bioreactors in the treatment of

248 Pages·2016·9.39 MB·English

SYSTEM AND FOULING PERFORMANCES OF ANAEROBIC
CERAMIC MEMBRANE BIOREACTORS IN THE
TREATMENT OF DOMESTIC WASTEWATER

YUE XIAODI
(B. Eng., National University of Singapore)

A THESIS SUBMITTED FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF CIVIL&ENVIRONMENTAL
ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2015
Declaration
I hereby declare that this thesis is my original work and it has been written by me in
its entirety. I have duly acknowledged all the sources of information which have been
used in the thesis.
This thesis has also not been submitted for any degree in any university previously.

Yue Xiaodi
21 Dec 2015
ACKNOWLEDGEMENT
I would like to express my sincere appreciations to my supervisors Prof. Ng
How Yong and Dr. Koh Yong Keat, Kelvin for their guidance and advices. My
deepest thanks also go to Mr. Harry Seah, Mr. Leonard Lin, Mr. Lee Ying Jie and Dr.
Tao Guihe from Technology Department, Public Utilities Board (PUB) for their
insights into Singapore’s water industry when I was searching for research direction.
I would also like to thank my scholarship awarder – National Research
Foundation (Environmental and Water Technology Program) as well as Mr. Eric Soh,
Ms. Linda Lim and Ms. Tina Tham from Environmental and Water Industry Office
for settling the administration matters.
I also wish to extend my appreciation to the staffs in Water Science and
Technology Laboratory – Mr. Chandrasegaran, Ms. Lee Leng Leng and Ms. Tan
Xiaolan for their kind assistances and supports. My heartfelt thanks go to my seniors,
Dr. Jin Le, Dr, Cai Bijing, Dr. Shi Xueqing, Dr. Ng Kok Kwang and Dr. Low Siok
Ling for their willingness to share their experiences with me. Not to forget my peers
in lab – Mr. Fu Chen and Ms. Mei Xiaojie for exchanging their valuable opinions and
taking care of my reactors when I was overseas.
Last but not least, I would also like to express my gratitude to my husband, Mr.
Chen Wenxian and my mother Ms. Huang Tuohui for their understanding, supports
and encouragements in all these years.
TABLE OF CONTENTS
SUMMARY ........................................................................................................................................... I
LIST OF TABLES ............................................................................................................................. IV
LIST OF FIGURES ........................................................................................................................... VI
NOMENCLATURE .......................................................................................................................... IX
SYMBOLS ......................................................................................................................................... XII
1 INTRODUCTION ...................................................................................................................... 1
1.1 RESEARCH BACKGROUND................................................................................ 1
1.1.1 AnMBR Development and Current Status ............................................ 1
1.1.2 Potentials of AnMBRs ........................................................................... 2
1.1.3 Membrane Fouling ................................................................................ 3
1.2 RESEARCH OBJECTIVES AND SCOPES .............................................................. 4
1.3 THESIS ORGANIZATION .................................................................................... 7
2 LITERATURE REVIEWS ........................................................................................................ 8
2.1 ANAEROBIC DIGESTION ................................................................................... 8
2.2 START-UP OF ANAEROBIC REACTORS ........................................................... 12
2.3 BIODEGRADATION-RELATED OPERATING CONDITIONS ................................ 12
2.3.1 Temperature ......................................................................................... 12
2.3.2 pH ......................................................................................................... 14
2.3.3 Carbon to Nitrogen Ratios (C/N) ........................................................ 14
2.3.4 Mixing .................................................................................................. 15
2.3.5 HRTs and SRTs .................................................................................... 15
2.3.6 Inhibition on Anaerobic Microbial Activities ..................................... 17
2.4 PERFORMANCES OF ANMBRS ....................................................................... 22
2.5 MEMBRANE FOULING .................................................................................... 25
2.5.1 Fouling Mechanisms ........................................................................... 25
2.5.2 Fouling Models .................................................................................... 29
2.5.3 Key Factors Affecting Membrane Fouling ......................................... 31
2.6 FOULING CONTROL METHODS ....................................................................... 53
2.6.1 Overall Description ............................................................................. 53
2.6.2 Physical Methods ................................................................................. 54
2.6.3 Chemical Methods ............................................................................... 59
2.6.4 Biological Methods .............................................................................. 61
2.7 CONCLUSIONS AND IDENTIFICATION OF RESEARCH GAPS ............................ 62
3 MATERIALS AND METHODS ............................................................................................. 63
3.1 CERAMIC MEMBRANES .................................................................................. 63
3.2 BIOFILM CARRIERS ........................................................................................ 64
3.3 REACTORS SETUP ........................................................................................... 64
3.3.1 Phase One ............................................................................................ 64
3.3.2 Phase Two ............................................................................................ 67
3.3.3 Phase Three ......................................................................................... 69
3.4 SAMPLING METHODS ..................................................................................... 71
3.4.1 Biomass, Feedwater and Permeate Sampling .................................... 71
3.4.2 SML & EPS Preparation ..................................................................... 71
3.4.3 Foulants Extractions ........................................................................... 71
3.4.4 DNA Extraction and Amplification ..................................................... 72
3.5 ANALYTICAL METHODS ................................................................................. 72
3.5.1 General Analytical Methods................................................................ 72
3.5.2 Dissolved Methane .............................................................................. 73
3.5.3 SMA Tests ............................................................................................ 74
3.5.4 Dehydrogenase Activities (DHA) ........................................................ 75
3.5.5 Pyrosequencing ................................................................................... 76
3.5.6 Proteins Assay ..................................................................................... 76
3.5.7 Carbohydrates Assay ........................................................................... 78
3.5.8 Excitation and Emission Matrix (EEM) .............................................. 79
3.5.9 Size Exclusion Chromatography ......................................................... 79
3.5.10 Membrane Visualization ..................................................................... 79
3.5.11 Resistance-in-Series Test ..................................................................... 80
3.5.12 Critical Flux Test ................................................................................. 80
3.5.13 Batch Membrane Cleaning Tests in Phase Three ............................... 81
4 FOULING MECHANISMS OF DIFFERENT PORE-SIZED MEMBRANES................ 82
4.1 START-UP OF THE ANCMBRS ....................................................................... 82
4.2 SYSTEM PERFORMANCES OF THE ANCMBRS ............................................... 85
4.3 DISSOLVED METHANE IN THE PERMEATE ...................................................... 86
4.4 COD BALANCE .............................................................................................. 88
4.5 RELATIONSHIP BETWEEN FOULING RATES AND MEMBRANE PORE SIZES .... 91
4.6 EFFECTS OF DOMS ON MEMBRANE FOULING ............................................... 97
4.6.1 Total Dissolved Organic Carbon (tDOC)........................................... 97
4.6.2 Low Molecular Weight Substances ................................................... 101
4.6.3 Biopolymers ....................................................................................... 105
4.7 CONCLUSIONS .............................................................................................. 111
5 FOULING MITIGATION BY BIOFILM CARRIERS ..................................................... 112
5.1 EFFECTS OF BIOFILM CARRIERS ON SYSTEM PERFORMANCES .................... 112
5.1.1 System Performances ........................................................................ 112
5.1.2 Microbial Activities in Mixed Liquor ................................................ 114
5.1.3 Microbial Community Distributions ................................................. 116
5.2 EFFECTS OF BIOFILM CARRIERS ON MEMBRANE FOULING BEHAVIORS ..... 119
5.3 PHYSIOCHEMICAL EFFECTS OF BIOFILM CARRIERS .................................... 121
5.3.1 Rheological Properties ...................................................................... 121
5.3.2 Structures of Bioflocs ........................................................................ 123
5.3.3 Mixed Liquor Soluble Products ........................................................ 127
5.4 PHYSICAL EFFECTS OF BIOFILM CARRIERS ................................................. 129
5.4.1 Morphologies of Cake Layers ........................................................... 129
5.4.2 Constituents in Cake Layers .............................................................. 131
5.4.3 Microbial Community Distributions in Cake Layers ....................... 132
5.5 CONCLUSIONS .............................................................................................. 133
6 MEMBRANE FOULING MITIGATION BY NACLO-ASSISTED BACKWASH ...... 135
6.1 EFFECTS OF NACLO ON SYSTEM PERFORMANCES ...................................... 135
6.1.1 Biomass Growth ................................................................................ 135
6.1.2 Treatment Efficiencies ....................................................................... 136
6.1.3 Microbial Activities ........................................................................... 140
6.1.4 Microbial Community Distribution ................................................... 143
6.2 EFFECTS OF NACLO ON MEMBRANE FOULING RATES ................................ 145
6.3 MEMBRANE FOULING MITIGATING MECHANISMS OF NACLO ................... 147
6.3.1 Direct Effect on Membrane Cleaning ............................................... 147
6.3.2 Indirect Effect on DOMs ................................................................... 150
6.3.3 Membrane Fouling Resistance Distributions ................................... 153
6.3.4 Accumulations of Foulants on Membranes ...................................... 154
6.4 CONCLUSIONS .............................................................................................. 160
7 CONCLUSION AND RECOMMENDATIONS ................................................................. 161
7.1 CONCLUSIONS .............................................................................................. 161
7.2 IMPLEMENTATIONS OF THE CURRENT STUDY ............................................. 162
7.3 FUTURE OPPORTUNITIES FOR RESEARCH ON THE ANMBR ........................ 163
8 BIBLIOGRAPHY ................................................................................................................... 165
SUMMARY
SUMMARY
Anaerobic membrane bioreactors (AnMBRs) have been regarded as a
potential solution to achieve energy neutrality in the future wastewater treatment
plant. Coupling ceramic membranes into AnMBRs offers great potential as ceramic
membranes are resistant to corrosive chemicals such as cleaning reagents and harsh
environmental conditions such as high temperature. However, membrane fouling is
still the biggest hindrance to the wide-spreading of AnMBRs. This study aimed to
mitigate fouling by selecting the proper pore sizes, adding biofilm carriers and
providing NaClO-assisted backwash.
In phase one, ceramic membranes with pore sizes of 80, 200 and 300 nm were
individually mounted in three anaerobic ceramic membrane bioreactors (AnCMBRs)
treating real domestic wastewater to examine the treatment efficiencies and to
elucidate the effects of dissolved organic matters (DOMs) on fouling behaviors.
When filtering mixed liquor of similar properties, smaller pore-sized membranes
fouled slower in long-term operations due to lower occurrence of pore blockages. The
major foulants were identified to be biopolymers that were produced in microbial
activities. One of the main components of biopolymers – proteins – led to different
fouling behaviors.
In phase two, biofilm carriers were added into AnCMBRs treating real
domestic wastewater to investigate their capabilities in fouling control. Three

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SUMMARY
AnCMBRs were dosed with biofilm carriers that made up 0, 10 and 20% of the
reactor volumes. It was found that higher dosages of biofilm carriers delayed
membrane fouling and improved the critical fluxes. The biofilm carriers mildly
sheared the bioflocs and decreased their sizes. The dispersed bioflocs allowed for
higher substrate utilization rates. Meanwhile, lower mixed liquor suspended solid
(MLSS) concentrations were developed in the AnCMBRs with higher dosages of
biofilm carriers. The biofilm carriers could also physically scour the membrane
surfaces. The collisions induced by the biofilm carriers resulted in cake layers that
were lighter, more porous and more amorphous. Cake layers with these properties
had much lower resistances than the thicker and denser cake layers in the AnCMBRs
without biofilm carriers. In conclusion, higher dosages of biofilm carrier could better
mitigate membrane fouling because of the reduced MLSS concentrations, increased
sizes of soluble products in mixed liquor and the physical scouring effects exerted by
the biofilm carriers.
In phase three, the NaClO-assisted backwash was used to further mitigate
fouling. NaClO had two effects on membrane fouling – indirect effects on the DOMs
and direct effects on membrane cleaning. When NaClO concentrations in the
backwash solutions were low, oxidization of DOMs improved their biodegradability,
microbial activities and membrane cleaning efficiencies. When the NaClO
concentrations in the backwash solutions were too high, the cell metabolisms were
deteriorated, leading to excessive productions of cell lytic products that resulted in
higher membrane fouling rates. Therefore, higher NaClO concentrations in the
backwash solutions should be used as long as the microbial activities were not
reduced.
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SUMMARY
In conclusion, membrane fouling could be mitigated the most effectively with
the combinations of smaller pore sizes, higher dosages of biofilm carriers and highest
NaClO concentrations in the backwash solutions that did not lead to reduced
microbial activities.
Keywords: Anaerobic membrane bioreactor, biofilm carriers, ceramic
membrane, chemically-assisted backwash, COD balance, dissolved organic matters,
low-strength wastewater, membrane fouling

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