Using polyaluminum chloride and polyacrylamide to control membrane fouling in a cross-flow anaerobic membrane bioreactor

The objective of this study is to determine the feasibility of using flocculants to control membrane fouling in anaerobic membrane bioreactors (AnMBRs), which has not been previously reported. The effects of two typical polymeric flocculants, polyaluminum chloride (PAC) and polyacrylamide (PAM), on the properties (filterability, soluble microbial products (SMP), zeta potential and floc size) of anaerobic sludge were studied by batch experiment. The addition of either PAC or PAM can improve the filterability of the mixed sludge liquor but with different mechanisms and dosages. PAC mainly decreases the SMP, while PAM enlarges the floc size. The recommended PAC dosage is 500 mg/L because a higher dosage would cause significant inhibition to anaerobic digestion. The effects of three flocculant addition methods on membrane fouling were tested in two lab-scale anaerobic membrane bioreactors. PAC at a dosage of 500 mg/L was shown to be more effective than PAM in the control of membrane fouling through the reduction of TMP and the rate of TMP increase by facilitating the decrease in SMP and the improvement of sludge filterability. The addition of PAC at the beginning of the operation was the best way to control membrane fouling as the running period could be effectively extended.