Development of Aerobic Granular Sludge Membrane Bioreactor (AGMBR) to Mitigate Fouling
Date
2019-09-04
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Abstract
In this research, the integration of aerobic granular sludge and membrane filtration to develop aerobic granular sludge membrane bioreactor (AGMBR) was explored. The main focus was on the in-depth study of extracellular polymeric substances (EPS) in AGMBR. Firstly, the long-term stability of aerobic granules (AG) was investigated in a sequencing batch reactor (SBR). This was followed by an in-depth analysis of EPS in a continuous-flow submerged AGMBR. And, the capability of AGMBR to remove organic matter, nitrogen, and phosphorus was determined. The combined strategy of long anaerobic slow feeding, fixed 1:3 ratio of feast-famine period within each SBR cycle, and continuous wasting of mature granules controlled EPS content at a suitable level to allow for long-term AG stability. High proteins/polysaccharides (PN/PS) ratios for loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) allowed for stable reactor operation for over 240 d without AG disintegration. EPS producers - Thauera, Flavobacterium and Meganema - and slow growing bacteria - Acinetobacter and Simplicispira - contributed to AG stability. The AGMBR exhibited high PN in the TB-EPS, resulting in high PN/PS ratios of 2–16. AG trapped most of the EPS in their matrix. Low soluble EPS resulted in acceptable rise in transmembrane pressure at membrane flux of 12.5 L/m2.h. An increase in soluble EPS PN correlated with increase in membrane fouling (r = 0.581). Compared to conventional membrane bioreactor, the AGMBR achieved seven times reduction in permeability maintenance cleaning frequency of the membrane. The COD showed a significant main effect on both PN and PS components of TB-EPS at α < 0.05. Water jet easily sloughed off the developed membrane cake layer, eliminating the need for chemical cleaning. The AGMBR system achieved 98.7±1%, 99.7±0.5%, 50±30%, and 35±18% removal for organic matter, ammonia-nitrogen, total nitrogen, and phosphorus, respectively. Meganema and Thauera, responsible for organic matter degradation, were present throughout the experimental duration. Nitrosomonas and Nitrospira allowed for complete nitrification. The presence of Azoarcus and Thauera points to anoxic conditions in AG, indicating some denitrification activity. Negligible phosphorus-accumulating organisms were detected; hence, the low phosphorus removal is attributed mainly to consumption for growth, struvite and biologically induced precipitation pathways.
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Keywords
Aerobic granular sludge (AGS), Aerobic granular sludge membrane bioreactor (AGMBR), Extracellular polymeric substances (EPS), Membrane fouling, Wastewater treatment
Citation
Iorhemen, O. T. (2019). Development of Aerobic Granular Sludge Membrane Bioreactor (AGMBR) to Mitigate Fouling (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.