Correlating membrane fouling with sludge characteristics in membrane bioreactors: an especial interest in EPS and sludge morphology analysis.

Two submerged membrane bioreactors were operated for a period of 3 months to study the filtration behavior of normal sludge and bulking sludge. Comparison of sludge morphology and bound extracellular polymeric substances (EPS) from the two systems was made to elucidate the different filtration characteristics. Experimental results showed that the membrane fouling behavior induced by bulking sludge was more severe than normal sludge. Concomitantly, the adsorption tests and atomic force microscopy observation confirmed that the EPS properties played an important role in membrane adsorption, eventually causing the different fouling behavior. Correlations between image analysis information and diluted sludge volume index (DSVI) have been identified. The combinations of EFLI/FAI (the ratio between extended filamentous lengths and floc area), from factor and floc elongation related parameters (aspect ratio or roundness) were the preferred input candidates in autoregressive exogenous model to describe the filamentous bulking phenomena, which aided in predicting membrane fouling.