Impacts of highly turbid water on microfiltration with coagulation pretreatment

The high turbidity of the raw water impedes the application of membrane filtration. Elevated concentration of particles has been occurred in intake water for a drinking water in Korea, especially during a rainy season. Effects of the high turbidity waters on microfiltration were investigated. Due to the fluctuated inflow of particles as well as organic matter in the intake water, conventional water treatment processes including coagulation, sedimentation, and filtration have been applied in the drinking water plant. Coagulation was applied as a pretreatment for the microfiltration with an immersed type of module. In addition to particles from the raw water, great amounts of flocs produced from the coagulation pretreatment process could aggravate the immersed membrane system. The turbid matter in the river water was concentrated and spiked to produce the desired concentrations (i.e., up to approximately 39 NTU and 220 NTU). Kaolin particles were also used with similar concentrations. Membrane flux decline behaviors of samples and the cake resistances on membrane surfaces were investigated. It has shown that adding kaolin particles to the raw water was beneficial to flux. The results from experiments with the increased turbidity by natural particles showed the relatively great flux decline, probably due to organic matters adsorbed to the particles. Coagulation pretreatment showed improvement in water production, regardless of applying a settling process, compared to the raw water. However, the flux decline of pretreated water was greater when settling was not applied. Therefore, we could conclude that coagulated flocs from a high turbidity water could decrease water production of microfiltration, especially when NOM concentration is significant.