Assessing the interaction effects of coagulation pretreatment and membrane material on UF fouling control using HPSEC combined with peak-fitting

• PVC based UF membrane retained only biopolymer fraction organic.
• Besides biopolymer, CA based UF membrane also retained low MW organics.
• Alum coagulation had higher removal of biopolymer than that of low MW acids.
• The efficiency of alum pre-coagulation on CA membrane fouling control was inferior to that on PVC membrane.

In this paper, the effects of alum coagulation pretreatment on the removal of natural organic matter (NOM) from surface water, and on fouling control of the subsequent ultrafiltration (UF) membrane filtration, were studied. Two kinds of UF membrane, made from polyvinyl chloride (PVC) and cellulose acetate (CA), respectively, were tested. The dissolved organics were characterized by high performance size exclusion chromatography (HPSEC) with ultraviolet/visible (UV/vis) and dissolved organic carbon (DOC) detectors, in addition to the conventional organic parameters, such as nonpurgeable dissolved organic carbon (NPDOC) and UV254. The results show that coagulation pretreatment could reduce the flux decline of UF membrane filtration by removing some of the NOM. Alum coagulation was found to have higher removal for large molecular weight organics, such as biopolymers and humic substances, than for low molecular weight acids. The results from HPSEC revealed that the PVC membrane removed mainly the biopolymer fraction, while the CA membrane, in addition to biopolymers, also removed some of the more hydrophilic low molecular weight acids. As alum coagulation preferably removed biopolymers over low molecular weight acids, pre-coagulation had less effect on CA membrane flux decline control than on PVC membrane flux decline control.