Development of Specific Granular Growth Anaerobic Membrane Bioreactors for Domestic Wastewater Treatment

Abstract

In recent years, water scarcity has brought global health and environmental concerns. To overcome this issue, anaerobic granular membrane bioreactors (G-AnMBRs) have been widely used for reclaiming domestic wastewater. However, there were still critical issues associated with G-AnMBRs, such as membrane fouling and granule fragmentation.

This thesis focused on developing a novel sponge-based G-AnMBR for domestic wastewater treatment. Results showed that the G-AnMBR start-up could be successfully accomplished using flocculent aerobic sludge as the inoculum. Hydraulic retention time (HRT) of 12 h permitted better organic removal and superior granular sludge quality. The external G-AnMBR (EG-AnMBR) served as a better G-AnMBR configuration due to less fouling propensity and superior granule quality. Membrane direct incorporation into the submerged G-AnMBR (SG-AnMBR) significantly enhanced microbial products (e.g. soluble microbial products (SMP) and extracellular polymeric substances (EPS)) in the mixed liquor and cake layer, and reduced granules EPS content and settleability. The EG-AnMBR demonstrated less SMP and EPS in the mixed liquor and cake layer, which might reduce the cake layer resistance and lower fouling rate.

The sponge assisted-granular anaerobic membrane bioreactor (SA-GAnMBR) showed enhanced treatment performance than the converntional G-AnMBR (CG-AnMBR). Granular sludge from the SA-GAnMBR had superior quality with better settleability, larger particle size, higher EPS content and more granule abundance. The SAGAnMBR also exhibited slower fouling development with 50.7% lower total filtration resistance than those of the CG-AnMBR. Sponge addition effectively reduced the concentration of microbial products in the cake layer and settling zone mixed liquor, and lowered the concentrations of major foulant organics, thus alleviating the fouling propensity.

The new hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor (SAAMB-AnGMBR) showed organic removal efficiencies over 94% at all COD/N (C/N) ratio conditions. Nutrient (nitrogen and phosphate) removal was over 91% at C/N ratio of 100/5 but was negatively affected when decreasing C/N ratio to 100/10. At lower C/N ratio (100/10), more noticeable membrane fouling was caused by aggravated cake formation and pore clogging, and EPS accumulation in the mixed liquor and sludge cake as a result of deteriorated granular quality. Significant difference existed in the foulant organic compositions under different C/N ratios. The performance of the hybrid system was found to recover when gradually increasing C/N ratio from 100/10 to 100/5. This work aimed to offers a useful performance enhancement and fouling control strategy for G-AnMBR operation, and provide a solid platform for advances in novel G-AnMBR applications for domestic wastewater treatment.