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Title: Submerged anaerobic membrane bioreactors : fouling, phage removal and flowsheet models
Author: Fox, Rachel Alison
ISNI:       0000 0004 2741 7308
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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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.
Supervisor: Stuckey, David Sponsor: Royal Society
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral