Evaluation of autotrophic process influencing extracellular polymeric substances in aerobic membrane bioreactor with expanded ASM model

Abstract

A mathematical model was developed to predict the formation of both the autotrophic and heterotrophic extracellular polymeric substances (EPS) in the aerobic membrane bioreactor (MBR). Batch experimental results and 45-day operation data on a pilot MBR at a sludge retention time (SRT) of 20 d were used to calibrate and validate the model. Simulated MBR setup results demonstrated the key role of the influent COD and NH₄⁺-N in governing the composition of heterotrophic and autotrophic EPS in the MBR. These results also revealed that the autotrophic EPS process was non-ignorable in the system. According to the autotrophic EPS simulation in the MBR, the EPS yield increased with increasing influent COD/NH₄⁺-N ratio towards a constant level. The EPS yield was significantly influenced by the SRT, attributed to the autotrophic process's impact on EPS. Simulation results revealed a slight increase in EPS yield with an SRT of up to 5 days, followed by a rapid decrease beyond that threshold.

Keywords: Autotrophic process; Expanded activated sludge model (ASM); Extracellular polymeric substances (EPS); Membrane bioreactor (MBR).