Comparison of the effects of aluminum and iron(III) salts on ultrafiltration membrane biofouling in drinking water treatment.

Coagulation plays an important role in alleviating membrane fouling, and a noticeable problem is the development of microorganisms after long-time operation, which gradually secrete extracellular polymeric substances (EPS). To date, few studies have paid attention to the behavior of microorganisms in drinking water treatment with ultrafiltration (UF) membranes. Herein, the membrane biofouling was investigated with different aluminum and iron salts. We found that Al2 (SO4 )3 ·18H2 O performed better in reducing membrane fouling due to the slower growth rate of microorganisms. In comparison to Al2 (SO4 )3 ·18H2 O, more EPS were induced with Fe2 (SO4 )3 ·xH2 O, both in the membrane tank and the sludge on the cake layer. We also found that bacteria were the major microorganisms, of which the concentration was much higher than those of fungi and archaea. Further analyses showed that Proteobacteria was dominant in bacterial communities, which caused severe membrane fouling by forming a biofilm, especially for Fe2 (SO4 )3 ·xH2 O. Additionally, the abundances of Bacteroidetes and Verrucomicrobia were relatively higher in the presence of Al2 (SO4 )3 ·18H2 O, resulting in less severe biofouling by effectively degrading the protein and polysaccharide in EPS. As a result, in terms of microorganism behaviors, Al-based salts should be given preference as coagulants during actual operations.