Hydraulically irreversible membrane fouling during coagulation-microfiltration and its control by using high-basicity polyaluminum chloride

The extent of hydraulically irreversible membrane fouling in a coagulation-filtration system depends on several factors, including properties of the coagulant. Effects of polyaluminum chloride (PACI) coagulant properties, specifically basicity and sulfation, were investigated by conducting long-term direct filtration experiments. Elemental analysis determined Al and Si to be the major foulants, though the Si/Al ratios of the foulants differed from those of coagulated floc particles. While floc particle size depended on the concentrations of sulfate ions and polymeric species in the PACIs, floc-size changes did not affect transmembrane pressure (TMP) buildup and thus did not affect irreversible fouling. Differences in PACI basicity, which affected the distribution of aluminum species, resulted in changes to the degree of irreversible fouling. Pretreatment with high-basicity (71%) PACI was superior to pretreatment with normal-basicity (51%) PACI in reducing irreversible fouling and attenuating TMP buildup during filtration. Higher basicities resulted in less Al breakthrough and a decrease in the Si/Al ratio of the foulants. However, IMP buildup was the same for PACIs with basicities of 71% and 90%; therefore, TMP buildup is not simply related to Al breakthrough and deposition. Increasing the basicity of PACIs would be an effective way to reduce the amount of foulant deposited on the membrane by decreasing the amount of aluminum that passes through the membrane. (C) 2014 Elsevier B.V. All rights reserved,