Effect of operational parameters on sludge accumulation on membrane surfaces in a submerged membrane bioreactor

In the present study, an orthogonal array design was adopted to investigate effects of operational parameters including aeration intensity, membrane flux, suction time and non-suction time on sludge accumulation on membrane surfaces respectively at a high SS concentration of 10 g l(-1) and a low SS concentration of 1 g l(-1) in a submerged membrane bioreactor. Average transmembrane pressure (TMP) increase rate over the operation time was used to evaluate sludge accumulation. Among the four factors, membrane flux was found to influence TMP the most obviously. The effect of aeration intensity became significant only at a high SS concentration of 10 g l(-1). TMP increased with suction time and decreased with non-suction time. There was a critical membrane flux over which sludge particles were deposited, and accordingly, TMP increased sharply. Two zones, predicting whether sludge particles are deposited or not, could be comprehensively determined by the critical flux, correspondent aeration intensity and SS concentration. For long-term stable operation, it is suggested that a membrane bioreactor be operated in the zone with prediction of no obvious sludge deposit on membrane surfaces.