Arsenic Remediation of Drinking Water using Limestone

The Environmental Protection Agency (EPA) has proposed lowering the Maximum Contaminant Level (MCL) for arsenic, currently set at 50 ppb, to 10 ppb or less. Current remediation technologies are expensive. This will result in increased economic pressure on rural communities with high levels of arsenic in their drinking water. The proposed lower MCL for arsenic has spurred the development of appropriate new technologies. Arsenic, at pH 8.0 and above, is known to be readily soluble and transports easily through ground water. Previous work indicates that arsenic has significant retention in contact with calcium and magnesium carbonates. This could be a result of adsorption on the limestone and dolomite mineral surfaces or precipitation. Adsorption batch tests with crushed limestone have been shown to reduce arsenic from 100 ppb to \u3c5 ppb. Batch tests comparing the efficiency of arsenic removal using different types of limestone have been performed, including a low magnesium limestone (~3%) and a high magnesium limestone (~27%). Three grain sizes were tested (\u3c0.589 mm, 0.5-1 mm, and 1-2 mm) to examine the efficiency of arsenic removal as a function of surface area. Scanning electron microscopy was used to determine surface morphology. The removal of arsenic in the presence of Fe2O3 mixed with limestone was also determined. Column studies have been initiated to examine the use of limestone as a practical method for removal of arsenic. The potential for bacterial growth on the limestone material in the columns under conditions of intermittent usage is being investigated