Influence of Operating Condition and Suspension Characteristics on Membrane Fouling in Membrane Bioreactors

In this study, the influence of the food-to-microorganism ratio (F/M) and permeate flux on membrane fouling was investigated using pilot-scale membrane bioreactors (MBRs) fed with actual municipal wastewater. Membrane fouling rate was affected by both F/M and permeate flux. It was shown that the influence of permeate flux on the membrane fouling rate was more significant than that of F/M. Batch filtration experiments were conducted to evaluate the degree of irreversible fouling caused by different fractions (suspended solids, colloids, soluble matter) in the mixed liquor of MBRs. From the results of the batch experiments, it was revealed that (a) irreversible fouling was caused mainly by the soluble fraction, and (b) irreversible fouling became significant when the MBR operated with a high F/M and a short solid retention time. There was a relationship between the fouling rate and the concentration of dissolved organic carbon (DOC) particles in the mixed liquor, whose size was between 0.2 μm and 0.5 μm. The concentration of organic matter with an apparent molecular weight of around 1MDa was also correlated with the fouling rate. These two constituents in the mixed liquor suspension seemed to affect membrane fouling.