Performance of gravity-driven membrane filtration for treatment of low-temperature and low-turbidity water: Effect of coagulation pretreatment

Abstract

As a promising technology for decentralized drinking water treatment, performance of gravity-driven membrane (GDM) filtration for low-temperature and low-turbidity water purification and effects of coagulation pretreatment were investigated in this study. Flux development and permeate water quality of three GDM systems, i.e., control GDM without pretreatment, GDM with in-line coagulation (IC) pretreatment (IC-GDM), GDM with coagulation-sedimentation (CS) pretreatment (CS-GDM), were compared. Moreover, composition and morphology of bio-cake layer were characterized to explain underlying mechanisms for performance improvement by coagulation pretreatment. Results suggested that permeate flux of control GDM stabilized at ∼4.0 L/(m2·h) for raw water with relatively low temperature (8.1– 10.8 °C) and turbidity (1.15– 2.47 NTU). IC pretreatment increased stable flux by 65 %, although the bio-cake layer thickness in IC-GDM was increased by 71.7 %, probably due to a significant reduction (57.1 %) in extracellular polymeric substances (EPS) in the bio-cake layer. Meanwhile, CS pretreatment increased stable flux by 87.5 %, which can be attributed to 63.3 % reduction in EPS and 47.0 % decrease in bio-cake layer thickness. As for permeate water quality, dissolved organic matter (DOM) was significantly reduced by both IC and CS pretreatments, mainly due to transformation from dissolved state to particulates. Compared with control GDM, both IC and CS pretreatments resulted in decrease in microbial abundance and activity and changes in microbial community, probably due to decrease in bioavailable phosphate and DOM. This study suggested that both IC and CS pretreatments can be integrated with GDM filtration for efficient purification of low-temperature and low-turbidity water.