Hybrid microfiltration (MF)–ultrafiltration (UF) and hybrid coagulation–ultrafiltration membrane processes were investigated and compared for dissolved organic matter (DOM) reduction in the low turbidity raw water supply from Sri-Trang Reservoir, Thailand. The coagulation process was operated with 20 mg/L polyaluminum chloride (PACl) at pH 7. The MF used had a pore size of 0.1 μm and the UF was of immersible polysulfone hollow fiber membrane with a pore size of 0.008 μm. The hybrid coagulation–UF process could effectively reduce DOM in terms of dissolved organic carbon (DOC) and UV-254 by 64% whereas the hybrid MF–UF membrane process yielded lower efficiency, 58% DOC reduction and 50% UV-254, respectively. In regards to trihalomethane formation potential (THMFP) analysis, the hybrid coagulation–UF membrane process showed slightly higher efficiency in THMFP reduction than that of the hybrid MF–UF process, 87.6 and 87.1%, respectively. The resin adsorption technique using DAX-8 was also employed to fractionate DOM in all water samples into two fractions; hydrophobic (HPO) and hydrophillic (HPI) organic matter. Significantly, HPO was the major fraction of DOM in the raw water source and it was the main precursor of THMFP.

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