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257d

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

Yasuhito Mukai, Tatsuhiko Hirano, and Eiji Iritani. Department of Chemical Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, Japan

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), 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. Also, the pretreatment by flocculation or adsorption and the combination with ozone treatment have been developed to reduce the membrane fouling.

In this study, a method has been developed for removing humic substances by hybrid ultrafiltration combined with both flocculation and adsorption treatments. Flocculation by use of poly aluminum chloride (PACl) was specially effective for the removal of humic acids referred to the relatively high molecular weight fractions of humic substances, whereas adsorption by use of powdered activated carbon (PAC) was able to remove fulvic acids of relatively low molecular weight effectively which could not be fully flocculated by PACl. Consequently, the combined operation of flocculation and adsorption was extremely effective for the treatment of humic substances. It was shown that both flocculation and adsorption characteristics of humic substances were strongly influenced by the solution pH. Hybrid ultrafiltration in combination with flocculation and adsorption treatments exhibited high permeate flux with high permeate quality. It was appeared that the dosages of both PACl and PAC exert a large effect on the filtration performance, and that there exist the optimum dosages of PACl and PAC.