Significant role of membrane fouling and microbial community on the performance of membrane bioreactor (MBR) system

The performance of a lab-scale membrane bioreactor (MBR) was evaluated based on its microbial community as well as the mechanism of membrane fouling. The growth of unwanted microorganisms in the system was observed, affecting effluent water quality. The MBR achieved a total-nitrogen removal of 56%. Nitrification and denitrification processes were most likely affected by the presence of Thiosphaera pantotropha, a bacterium capable of nitrification and denitrification processes. Phosphorus removal of 51% was attained, which is comparably lower than other existing systems. Furthermore, a chemical oxygen demand removal of 98% indicated the presence of active microbial community. However, this does not guarantee the existence of the target microorganisms. It was found that the increase in transmembrane pressure was caused by sludge-cake resistance rather than membrane-pore fouling. This conclusion was made by analyzing particle-size distribution and quantifying extracellular polymeric substances particularly soluble microbial products. The fouling mechanism was investigated by analyzing the membrane surface image generated by confocal laser scanning microscopy and scanning electron microscopy, and confirmed that MBR sludge were easily removed by physical cleaning. Hindering the growth of undesirable organism and controlling the concentration of soluble microbial product, which causes severe fouling, could lead to an efficient performance of MBR system.