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  • Submerged Anaerobic Membrane

    Bioreactors: Fouling, Phage Removal and

    Flowsheet Models

    By Rachel Alison Fox

    A thesis submitted for the degree of Doctor of Philosophy

    of

    Imperial College London

    Department of Chemical Engineering

    Imperial College London

    London SW7 2AZ

    November 2012

    Date goes here

  • 1

    It is declared that the work presented in this thesis is the candidates own, all else has been

    appropriately referenced.

    ‘The copyright of this thesis rests with the author and is made available under a Creative

    Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy,

    distribute or transmit the thesis on the condition that they attribute it, that they do not use

    it for commercial purposes and that they do not alter, transform or build upon it. For any

    reuse or redistribution, researchers must make clear to others the licence terms of this work’

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    Abstract This thesis focuses on the Submerged Anaerobic Membrane Bioreactor (SAMBR). The aim of

    this work was threefold; firstly, to investigate the effect of certain system parameters on

    membrane fouling in the SAMBR; secondly, to monitor phage removal in the SAMBR; and,

    finally to assess the viability of anaerobic wastewater treatment processes (including the

    SAMBR) to treat domestic sewage (rather than sludge) for full scale operations in the UK. Using

    a Kubota flat sheet membrane with 0.4µm pores, the critical flux was found to be 11.8 lm-2h-1

    (litres per meter squared per hour or LMH), similar to those found by other researchers. The

    existence of a critical gassing rate was investigated (‘there exists a critical gassing rate which

    when reached causes a steep rise in transmembrane pressure (TMP)’), and was determined to

    be 4 litres per minute (LPM) or 2.4 m3m-2h-1; more interestingly, this appeared to happen at

    the changeover between a slug flow regime and bubble flow. The viscosity of the biomass in

    the SAMBR was found to be 2.5 times greater than water with the colloid fraction having the

    largest impact on the overall viscosity. The build-up of foulants on the membrane was thought

    to be the cause of a 10 fold increase in molecular weight cut off that was observed after

    operation beyond the critical flux and gassing rate. In addition, after extensive fouling some

    removal of volatile fatty acids (VFAs) was observed from 3.35% acetate removal to 5.9%

    removal of isovalerate, and this was not likely to be due to degradation across the membrane,

    but was thought to be due to electrostatic repulsion by the biofilm.

    The removal of bacteriophages by the SAMBR was used as a model for the removal of

    pathogenic viruses. Before critical operation (and the resulting jump in TMP), the smallest

    phage (MS-2) showed removals of between 1.8 - 2.1 log removal value (LRV), while the larger

    T4 phage showed removals from 5.1 - 5.3 log. Once critical operation had occurred, and the

    TMP increased, the T4 phage had a log removal greater than 7. The MS-2 phage, after

    operation beyond the critical parameters, showed a log removal dependence on the gas

    scouring rate. The LRV varied from 3.0 at a low gassing rate up to 5.5 at the highest gas scour,

    and this was thought to be due to concentration polarisation effects. The effect of activated

    carbon on phage removal was also investigated; while PAC had little effect, the addition of

    GAC to the SAMBR actually caused an increase in phage throughput. Finally, a range of

    potential flowsheets for anaerobic wastewater treatment were modelled. It can be concluded

    from this work that anaerobic treatment is a practical and promising alternative to

    conventional activated sludge plants. In addition, the SAMBR was found to be the most

    favourable anaerobic unit. However, it was noted that there is still a lack of full scale data for

    this unit, thus further emphasising the importance of research into this technology.

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    Acknowledgements

    First of all I would like to thank my supervisor Professor David Stuckey for taking me on as a

    PhD student. I am grateful to David for his motivating enthusiasm for the subject of anaerobic

    wastewater treatment and also for our many and varied discussions both related to the

    subject and on non-academic matters.

    Throughout my PhD I have neither gone hungry nor homeless, for this I am very grateful to the

    Royal Society for generously funding this project and my bursary.

    I would like to thank all my colleagues in BSE, in particular Yannis, Antoine and Miao who took

    the time to teach me at the beginning. Also to Patricia, Nazri and Bonahis, for many interesting

    discussions on anaerobic digestion, I wish you the very best of luck with your projects.

    Of all my colleagues, Hafiz deserves a special thank you, partly for helping mop up my

    numerous blunders and partly for assisting my attempts to fix broken equipment but mostly

    for putting up with my questionable taste in lab music for three years.

    In addition to the scientific challenges presented in a PhD, there have also many administrative

    ones. From health and safety paperwork to complicated purchase orders my thanks to Susi,

    Sarah and Severine for their help with those pesky forms.

    It is important for me to acknowledge the help and support of my family during my PhD. Their

    comments, ranging from “Eeww you’re working with sewage” to “Surely, you will be finished

    soon”, were invaluable to my self-esteem throughout this project.

    Many thanks also to the various housemates, labmates and othermates who supplied the

    copious quantities of tea, cake and sympathetic ears required to complete this work. Finally to

    all the postgrads who advised me not to take on a PhD: Thanks for not saying “I told you so”

    during the difficult parts.

  • 4

    Notation

    ABR anaerobic baffle reactor

    BMP biochemical methane potential

    CAPEX capital expenditure

    COD chemical oxygen demand

    CSTR continuous stirred tank reactor

    ECP extracellular polymeric substances

    EPS extracellular polymeric substances

    GAC granular activated carbon

    HRT hydraulic retention time

    LMH litres per meter squared per hour

    LPM litres per minute

    LRV log removal value

    MBR membrane bioreactor

    MWCO molecular weight cut off

    OPEX operational expenditure

    PAC powdered activated carbon

    PCTE track-etched polycarbonate

    PEFE track-etched polyester

    PTFE polytetraflouroethylene

    PFD process flow diagram

    RPM rotations per minute

    SAMBR submerged anaerobic membrane bioreactor

    SEC size exclusion chromatography

    SMP soluble microbial products

    SRT solids retention time

    STW sewage treatment works

  • 5

    TMP trans-membrane pressure

    TSS total suspended solids

    UASB upflow anaerobic sludge blanket

    VFA volatile fatty acids

    VSS volatile suspended solids

    WWTP wastewater treatment plant

    µmax maximum growth rate (T -1)

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    Contents

    Chapter 1. Introduction ............................................................................................................ 15

    Chapter 2. Literature Review ................................................................................................... 20

    2.1 Anaerobic digestion ....................................................................................................... 20

    2.1.1 Hydrolytic Bacteria ................................................................................................ 20

    2.1.2 Acidogenic bacteria ............................................................................................... 21

    2.1.3 Acetogenic bacteria ............................................................................................... 22

    2.1.4 Methanogens ........................................................................................................ 23

    2.1.5 Role of Hydrogen ................................................................................................... 23

    2.1.6 Monod kinetics ...................................................................................................... 23

    2.2 Anaerobic reactor types ................................................................................................. 26

    2.2.1 Anaerobic Baffled Reactors (ABR) ......................................................................... 26

    2.2.2 Upflow anaerobic sludge blanket (UASB) reactor ................................................. 29

    2.2.3 Submerged Anaerobic Membrane Bioreactors (SAMBRs) .................................... 30

    2.3 Reactor setup ................................................................................................................. 33

    2.3.1 Reactor Configurations .......................................................................................... 33

    2.3.2 Membrane Types ................................

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