The effect of different static biocarriers on process performance, membrane fouling and microbial community in submerged membrane bioreactor treating municipal wastewater under high and low carbon/nitrogen ratios

This study investigated the impact of two different static biocarriers (polyvinyl chloride (PVC) and polyurethane (PU)) addition in MBR for process performance, membrane fouling and microbial community treating municipal wastewater under high and low carbon/nitrogen (C/N) ratios. The results indicated that PU biocarrier addition could help to accumulate the bacteria for nitrification and denitrification (Tauera, Amaricoccus and Nitrospira in the mixed liquor and Solitalea and Sphingobacteriales_unclassified on the biocarrier), which slightly enhanced the total nitrogen removal especially under a low influent C/N ratio of 6.7. Additionally, the PU biocarrier addition can also alter the bulk sludge characteristics with lower soluble microbial products (SMP) concentration, lower SMP protein to carbohydrates ratio and bigger particle size, leading to lower membrane fouling propensity even under a low influent C/N ratio. PU biocarrier addition also reduced the relative abundance of extracellular polymer substances (EPS) secretion-related bacteria (Sphingobacterials_unclassified and Ohtaekwangia) and mitigated the membrane fouling propensity. However, this is not the case with PVC biocarrier addition, which might be due to the physical properties of the static biocarrier since PU has higher porosity, specific surface area and less negative surface zeta potential than PVC. Importantly, the static biocarrier addition can improve the nitrogen removal especially under a low influent C/N ratio and facilitate the membrane fouling control, but it depends on the physical characteristics of the biocarriers.