A fourth objective was to identify residuals issues and associated management options, including costs and environmental impacts. Preliminary cost analyses were conducted to help guide utilities in process selection. Also included in the report are discussions of residuals management, costs, and a comparative assessment of treatment options. All processes examined, conventional and advanced, proved significantly more effective in arsenate removal than in arsenite removal. Activated alumina is applicable to waters with relatively low arsenic and relatively high sulfate, and provides long runs with low levels of arsenic.
Ion exchange is applicable to low sulfate waters, with provision of low levels of arsenate.
Microfiltration with coagulant dosing is applicable to high arsenic removal at new facilities, with lower sludge volumes than those from optimized conventional treatment. Subsequent pilot tests were performed to evaluate microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. Full-scale testing was performed to evaluate optimization of conventional treatment and softening. Microfiltration, coupled with low-dose ferric chloride pretreatment, was demonstrated as a technically feasible method for arsenic removal. A residuals analysis showed that the residuals generated from arsenic treatment facilities vary in consistency and in arsenic concentration.