Impact of Soluble Microbial Products and Extracellular Polymeric Substances on Filtration Resistance in a Membrane Bioreactor

Membrane fouling is the main obstacle to the wide application of membrane bioreactors (MBRs). Soluble microbial products (SMP) and extracellular polymeric substances (EPS) have been reported to act as major foulants in the operation of MBR used for wastewater treatment. Thus, the distributions of SMP and EPS in the fouling layer are essential for understanding and controlling membrane fouling. The influence of micro-organism metabolites, such as SMP and EPS, on membrane fouling was examined during the operation of an MBR. Activated sludge samples were taken from a laboratory-scale MBR and used to investigate their filtration resistances in different phases. Results showed that accumulated SMP and EPS in the MBR had a negative effect on membrane filtration. Concentrations of SMP, particularly the SMP with molecular weight (MW) of 3-10kDa, were positively correlated to the pore-blocking resistance. Cake layer formation was the main factor resulting in membrane fouling, and the amount of EPS and the SMP with MW > 10 kDa had strong positive effect on cake layer resistance. Using the Fourier transform infrared spectroscopy (FTIR), in the cake layer the major components of the EPS were found to be proteins, polysaccharides, and humic substances, but the dominant components of the SMP were polysaccharides and humic substances. The results of this study would contribute towards a better understanding of behavior, composition, and fouling potential of SMP and EPS in MBR operation.