Optimization study of a hybrid alum coagulation-membrane filtration system for virus removal

Due to the intrinsically small sizes of enteric viruses (20–100 nm) and their relatively high resistance to most disinfectants, detection of viruses in treated drinking water is not a rare phenomenon. This study therefore evaluates various aspects involved in a hybrid alum coagulation-ultrafiltration (UF) system for virus removal. Coagulant doses (0, 1 and 10 mg Al³⁺/L) and pH conditions relevant to drinking water (pH 6–8) were investigated. With this hybrid system, removal was not attributable merely to MS2 adsorption to flocs and subsequent retention by UF membranes. MS2 removal comprises of inactivation by the effect of pH and coagulant and subsequently, rejection of virus-associated flocs by UF membrane. Coagulation with 1 mg Al³⁺/L at pH 6 and 7 resulted in an overall reduction brought about by an average of 0.62 log inactivation via the pH effect, 1.2 log inactivation by alum coagulant, and >5.4 log rejection by the 100 kDa polyethersulfone UF membrane. In contrast, negligible upstream inactivation was noted with a coagulant dose of 1 mg Al³⁺/L at pH 8, but 5.8 log rejection was attained with downstream UF filtration. By optimizing the conditions appropriate for upstream inactivation and subsequent membrane rejection, virus removal efficiencies can be enhanced.