Development of Hybrid Ultrafiltration Combined with Both Flocculation and Adsorption Treatments for Advanced Removal of Humic Substances

Currently with the progression of the pollution in water sources, considerable attention has been given to the application of membrane filtration technology using microfiltration or ultrafiltration membranes to the surface water treatment as an alternative to conventional coagulation sedimentation and sand filtration. The microfiltration and ultrafiltration membranes are appropriate for complete removal of suspended solids or bacteria, but cannot completely remove such dissolved organic matter as the humic substances due to their small molecular size. The humic substances, which have become a problem as a trihalomethane precursor in the process of surface water treatment, mainly consist of humic acids of relatively high molecular weight (more than ca 1,500) and fulvic acids of relatively low molecular weight (less than ca 1,500) [1], and it is believed that it would be difficult to completely remove the humic substances by such single treatment as flocculation and adsorption because they have so broad molecular weight distribution. Moreover, the humic substances often cause the membrane fouling in the membrane filtration process, and therefore many researches on membrane filtration of humic acids of the high molecular weight fractions have been reported recently [1-8]. Also, the pretreatment by flocculation or adsorption and the combination with ozone treatment have been developed to reduce the membrane fouling [9-15]. In this study, hybrid ultrafiltration combined with both treatments of flocculation effective for humic acids and adsorption effective for fulvic acids is developed for removing humic substances. The validity of this method is verified from the standpoint of both filtration rate and rejection of solutes by conducting hybrid ultrafiltration of humic acids, fulvic acids and humic substances, respectively.