UF fouling behavior of allelopathy of extracellular organic matter produced by mixed algae co-cultures

Abstract The extracellular organic matter (EOM) produced during algae bloom can cause serious ultrafiltration (UF) membrane fouling. Most previous relevant studies focused on the UF fouling caused by the EOM from mono-algae. In this study, the UF fouling behavior of EOMs from three typical algae species (Microcystis aeruginosa (MA), Chlorella (Chl) and Scenedesmus obliquus (SO)) of both mono-culture and their co-cultures were examined in a comprehensive manner through a lot of analyses including the redundancy analysis (RDA), PARAFAC, AFM measurement, etc. The results showed that the UF performance was significantly affected by the humic-like and tryptophan-like substances in the EOMs. While their content from co-cultures showed clear and separate promotion and inhibition characteristics against the mono-culture. Concurrently, the membrane filtration behavior exhibited that the normalized flux followed the sequence of MA + SO > Chl + SO > Chl > SO > MA > MA + Chl. The flux drop during EOMs filtration from Chl + SO was close to the mono-algae, while MA + Chl produced the most serious fouling and MA + SO the least. The combined mechanism (CM) model was adopted to evaluate the fouling mechanism of EOM from both mono-culture and co-cultures. The results indicated that intermediate blocking had a larger predominance over standard blocking on EOM fouling from mono-culture, while standard blocking played the predominant part on co-culture fouling. Finally, the membrane morphology detection indicated the EOM from MA + Chl formed a compact foulant layer on the membrane surface, which was due to the existence of more hydrophobic micro-molecules in the culture and resulted in the most significant flux drop.