Can prechlorination improve the permeate flux and water quality of gravity-driven membrane (GDM) filtration?

Gravity-driven membrane (GDM) filtration is currently limited by the relatively low permeate flux and poor water quality. This study was aimed to investigate the effects of prechlorination (3 and 5 mgCl2/L) on the permeate flux and water quality in GDM filtration by analyzing the compositions and morphologies of the fouling layer and by evaluating virus removal and trihalomethane (THM) formation for short (7 cycles) and long (32 cycles) periods. Prechlorination showed an increased permeate flux, contributing to enhanced cumulative water production (15-68%), which was achieved by lowering the extracellular polymeric substances (EPS) content (14-31%) and the formation of a relatively thinner and looser fouling layer. Prechlorination effects lessened with longer GDM operation time owing to bacterial regrowth and formation of a thick (178-227%) and dense (57-66%) fouling layer. It also changed the dominant phylum in the eukaryotic community and limited its activities in the fouling layer. In terms of the permeate water quality, the prechlorination ensured microbial safety with a 3.2 log10 reduction of MS2 bacteriophage and negligible formation of THMs. These results demonstrate the potential of using prechlorination in GDM filtration for sustainable drinking water treatment.