Reduction of natural organic matter and membrane fouling in hybrid microfiltration drinking water treatment process

Abstract

The interest in ultra- and microfiltration membrane has increased due to the extremely high water quality in respect to hygiene and microbiological safety, documented by a growing number of UF and MF membrane installations. Compared to conventional treatment processes, low-pressure membranes provide further advantages beside the advantages of the independence of the permeate from raw water quality and the supply of a complete barrier against microorganisms and particles. But in treating surface waters, ultrafiltration or microfiltration applied as a single unit process are inappropriate due to hydraulic reasons, which is the limited yield caused by membrane fouling. Therefore, new and more effective methods of water treatments are being investigated. Coagulation and adsorption was applied for the pre-treatment of microfiltration of surface water to increase the contaminants removal and to decrease membrane fouling. Direct filtration of surface water without pretreatment showed both of poor removal of NOM less than 30% and high membrane fouling potential. PAC and GAC adsorption removed natural organic matter efficiently compared to the alum coagulation. Both of them removed the NOM having a molecular weight smaller than 1000 Dalton. In case of GAC adsorption, humic fraction which was not effectively removed by coagulation was preferentially removed. The hybrid MF system composed of coagulation-sedimentation, membrane filtration, and GAC adsorption, removed total 96% and 88% of TOC and UVA, respectively. Especially large MW NOM (1 k ~ 10 k Da) was effectively controlled by the combination of microfiltration and GAC adsorption. For the economic operation of process, GAC column was selectively operated based on UVA254 value with a set-point value of $0.035 cm^{-1}$, which value is equivalent to $50 \mu g/L$ of DBPFP. The selective operation of GAC column was effective in terms of process economy and effluent quality. Over than 33% of THMFP and HAAFP removal wer...