Characteristics of the sludge filterability and microbial composition in PAC hybrid MBR: Effect of PAC replenishment ratio

Periodic withdrawal and replenishment of powdered activated carbon (PAC) hybrid membrane bioreactor (MBR) is required for stable performance. The influence of the replenishment of powdered activated carbon (PAC) on sludge filterability and microbial community in hybrid MBRs was investigated. Results showed that the removal of organic matter and nitrogen were not significantly affected by the PAC refreshment, while soluble microbial products (SMP) concentration decreased and extracellular polymeric substance (EPS) increased with increasing PAC replacement ratio. MBR system with PAC replenishment exhibited low fouling propensity and prolonged filtration agreed well with fouling rate and resistance analysis. Molecular weight distribution of SMP in MBR confirmed the synergistic effects of PAC adsorption/biodegradation and membrane interception on organics removal. Microbial activity was positive associated with the PAC replenishment ratio. Moreover, the high-throughput sequencing indicated that due to fresh PAC added, the increased abundance of Proteobacteria, Bacteroidetes and Nitrospira guaranteed the pollutant removal, and the membrane fouling caused by Planctomycetes and Betaproteobacteria decreased. An optimal PAC replenishment ratio at 1.67% achieved the effective membrane fouling mitigation and enhanced dominant bacterial structure. PAC refreshment is considered to be a promising way to advance the application of MBR.