Regulated-biofilms enhance the permeate flux and quality of gravity-driven membrane (GDM) by in situ coagulation combined with activated alumina filtration

It is a critical challenge for drinking water production when treating algae-contaminated surface water. In this study, the impact of in situ coagulation (C), activated alumina filtration (AA) and their combination (CAA) on the performance of gravity-driven membrane (GDM) was systematically assessed during 105-day operation. The results indicated that pretreatments in particular CAA could effectively enhance GDM flux, and the stable fluxes were increased to 3.1, 4.9 and 8.3 L/(m 2 ·h) (LMH) for CGDM, AA/GDM and CAA/GDM, respectively when compared to the control GDM (2.0 LMH). Coagulation was beneficial to formation of thick but loose biofouling layer, while AA filtration was effective to retain foulants including extracellular polymeric substances (EPS), organics, total nitrogen and total phosphorus. The CAA/GDM could mostly remove these foulants, and facilitate the proliferation of bacterial genera that could consume EPS, further alleviating membrane fouling. The difference in loosely bound EPS and tightly bound EPS of biofouling layer attributed to the difference of reversible fouling and irreversible fouling, respectively. Morphological observations, variation in functional groups or elements further confirmed the difference in biological layers in different GDM systems. The occurrence of specific bacterial genera involving the potential to degrade protein, chitin and other high molecular weight organics was responsible for contaminant removals.