Effect of temperature variations in anaerobic fluidized membrane bioreactor: membrane fouling and microbial community dynamics assessment

Abstract

A single-stage anaerobic fluidized membrane bioreactor (AnFMBR) was applied to investigate the effects of temperature changes on membrane fouling while treating real municipal wastewater. The AnFMBR was operated at four temperature phases: 25 °C for 42 days, 20 °C for 20 days, 15 °C for 15 days, and at 10 °C for 15 days. The systems achieved a total chemical oxygen demand (TCOD) removal efficiency of above 90% at all phases. As temperature decreased, accumulation of solids and possible incomplete hydrolysis led to an increase in TCOD and volatile fatty acids (VFAs) in the reactor. However, as temperature reduced to 10 °C, VFAs in the reactor reduced probably an indication of reactors adaptation. Total membrane filtration resistance gradually increased to 1.1 × 1011 m−1 from 2.1 × 1009 m−1 with a temperature decrease from 25 °C to 10 °C. This corresponded to a significant decrease in membrane permeability from 1.68 to 0.05 LMH/kpa. The protein fraction of the extracellular polymeric substances (EPS) was dominant in all phases, which was ascribed for significant membrane fouling causing permeability deterioration. Microbial richness and diversity analysis using next generation Ion torrent sequencing methods revealed that Proteobacteria phylum was most dominant at 25 °C, whereas Bacteroidetes, which are responsible for releasing proteinaceous EPS, were most dominant at low temperatures (15 °C and 10 °C), contributing to severe fouling. In conclusion, decrease in temperature did not affect the treatment efficiency but resulted in gradual increase in membrane fouling.