Evaluation of a low-pressure membrane filtration for drinking water treatment: pretreatment by coagulation/sedimentation for the MF membrane

The immersed microfiltration (MF) membrane system combined with coagulation and sedimentation as a pretreatment was evaluated with respect to membrane flux, dissolved organic matter (DOM) removal, and the influence on membrane fouling properties. The pretreatment-combined membrane system demonstrates better performance in water production and DOM control than the direct filtration system without pretreatment. The pretreatment with coagulation and sedimentation improved the membrane performance for a sudden increase of solid loading and severe fluctuation of source water properties: in particular, the sedimentation step exhibited the capability of buffering the sudden shock of solid loading to the membrane, resulting in maintaining the stable flux and transmembrane pressure (TMP) in the membrane filtration. Even though pretreatment improved membrane performance, somewhat serious fouling was observed in the membrane due to the residual coagulant. The aluminum-based coagulant formed an inorganic scale with the silica originated from the source water, and then this inorganic scale was expected to accumulate in the membrane and promote severe organic fouling. Thus, the residual aluminum-based coagulant should be controlled to reduce membrane fouling in order to develop an improved system operation and an improved process design for the proposed system.