Technologies and Costs for Removal of Arsenic From Drinking Water

RegenerationRegeneration of AA beds is usually accomplished using a strong base solution, typicallyconcentrated NaOH. Relatively few BV of regenerant are needed. After regeneration with strongbase, the AA medium must be neutralized using strong acid; typically two percent sulfuric acid.Arsenic is more difficult to remove during regeneration than other ions such as fluoride (Clifford andLin, 1995). Because of this, slightly higher base concentrations are used; typically 4 percent NaOH.Even at this increased concentration , however, not all arsenic may be eluted. Clifford and Lin (1986)found only 50 to 70 percent of arsenic was removed from the AA columns during regeneration. Otherresearchers have also documented the difficult regeneration of AA for arsenic. Regeneration testsconducted by Benjamin et al. (1998) indicated that exposure of the AA medium to 0.1 N NaCl or 0.2N NaOH did not regenerate the AA to a significant extent. Arsenic recovery was limited and in mostcases was less than 50 percent of the sorbed arsenic. Higher recoveries have been reported, however.Hathaway and Rubel (1987) found that 80 percent of the adsorbed arsenic was eluted using 1.0 to 1.25M NaOH solution. Simms and Azizian (1997) found that up to 85% of the capacity of an AA bedcould be recovered using NaOH.Regeneration also affects successive bed life and efficiency. Bed life is shortened andadsorption efficiency is decreased by regeneration. Benjamin et al. (1998) found that arsenicbreakthrough patterns from the AA columns using regenerated media were qualitatively similar tothose using fresh media, but the removal efficiency declined slightly after each of two regenerations.Clifford (1986) demonstrated that regeneration has a clearly negative effect on the adsorptioncapacity of activated alumina. The unrecovered As(V) and changes in the AA surface induced by theregeneration process may cause the length of the adsorption runs to decrease by 10 to 15 percent aftereach regeneration.Field StudiesSeveral field studies have demonstrated that arsenic may be reduced to below 3 Fg/L usingactivated alumina filtration. For example, Stewart (1991) reports on the success of a small waterutility in treating for arsenic. This utility, which serves 89 households in Bow, New Hampshire,relies on 2 wells for its source water. Each of the wells is characterized by a high level of arseniccontamination (mean arsenic concentrations of 62 Fg/L and 57 Fg/L). However, the utility was ableto reduce arsenic levels below the current MCL of 50 Fg/L for 106 days while producing an average2-17