AWWA JAW65914

Because of the higher arsenic capacity of in situ-formed hydroxides and the growing popularity of zirconium and titanium oxyhydroxide media for arsenic removal, a comparative study of iron versus titanium and zirconium coagulants was conducted. Arsenite [As(III)] and arsenate [As(V)] removal using zirconium and titanium coagulants was compared with removal using ferric chloride (FeCl<;sub>;3<;/sub>;) and alum in a standard challenge water. As(III) adsorption was significantly lower than As(V) adsorption at all pH levels with all coagulants. The highest As(V) loadings both on mass and molar bases were observed with FeCl<;sub>;3<;/sub>;. As(V) removal increased with decreasing pH with all coagulants. The small amount of As(III) removal observed was generally independent of pH. Alum did not remove any As(III). The highest As(III) loadings were observed with titanium(III), which appeared to be oxidized to As(V) by peroxide resulting from titanium(III) hydrolysis. The types of sludge produced by all coagulants passed the toxicity characteristic leaching procedure and the waste extraction test. When chemical costs were compared, FeCl<;sub>;3<;/sub>; was the most cost-effective coagulant for As(III) and As(V) at all three pH values, and As(III) chemical coagulation costs were five to 20 times higher than those for As(V). Alum was four to eight times the cost of FeCl<;sub>;3<;/sub>; for As(V) removal. Includes 49 references, tables, figures.