Pre-Treatment of natural organic matters containing raw water using coagulation

Coagulation is a commonly adopted process as a pretreatment step for minimizing membrane fouling. Three coagulants, polyaluminum chloride (PACl), alum, and FeCl₃ were tested under four mixing-settling schemes for turbidity and natural organic matters (NOM) removal. The organic matters in the raw waters were fractionated by high performance size exclusion chromatography (HP-SEC) system and were characterized using the excitation-emission matrix (EEM) fluorescence spectra. Sufficient rapid mixing and slow mixing or applying two-stage coagulation benefit turbidity removal using PACl or FeCl₃ under "electrostatic patch coagulation" (EPC) mechanism. The EPC mechanism is not efficient for alum coagulation. At higher coagulant doses, the NOM removal is not affected by mixing condition. Intensive rapid mixing alone benefits NOM removal using PACl or FeCl₃. Alum is a poor coagulant for NOM removal under EPC mechanism.