Physicochemical correlations between membrane surface hydrophilicity and adhesive fouling in membrane bioreactors.

36 membrane material cases used in membrane bioreactors (MBRs) covering wide range of hydrophilicity/hydrophobicity were used to calculate thermodynamic interactions between membranes and foulants. It was found that adhesive fouling can be represented by the total interaction energy at minimum separation distance (h). No functional relationship between membrane hydrophilicity and adhesive fouling can be deduced. However, membrane hydrophilicity, in terms of water contact angle or interaction energy between two identical surfaces at h in water (ΔG), had high statistical correlations with adhesive fouling. This statistical correlations should be attributed to the major role of acid-base interaction in total interaction associated with adhesion in most of membrane cases. Moreover, the statistical correlations were independent of the changes in membrane surface roughness or hydrophilicity/hydrophobicity of foulants. These findings satisfactorily explained the inconsistent conclusions in the literature regarding effects of membrane hydrophilicity on adhesive fouling, giving implications for membrane fouling mitigation.