Enhanced As(III) removal with permanganate oxidation, ferric chloride precipitation and sand filtration as pretreatment of ultrafiltration

The potential of enhancing As(III) removal was investigated in a pilot study for the process of oxidation, precipitation and direct sand filtration as pretreatment before ultrafiltration. The pretreatment effectively facilitated As(III) removal and residual arsenic was below 10 μg/L for membrane effluent. Sand filters exhibit good potential for removing ferric precipitates with adsorbed arsenic, and membrane filtration is more significant in controlling effluent turbidity in this process. Permanganate was more promising than chlorine in this process, mainly ascribing to the positive seeding effects of in situ formed hydrous MnO2(s) and the formation of larger floc. A bench-scale study demonstrated the remarkable influence of in situ formed hydrous MnO2(s) on flocculant aggregation. The widely presented silicate (10 mg/L as Si) showed remarkable negative effects on arsenic removal. The process is effective in enhancing As(III) removal as a pretreatment for ultrafiltration; however, arsenic removal should be enhanced while silicate presenting to assure residual arsenic below 10 μg/L.