Arsenic Species Isoformation — A Key Problem for Water Purification

Abstract

Current research suggests that drinking water is the most common pathwayfor arsenic long-term low dose exposure. It would be advantageous toidentify treatment processes that economically remove arsenic frompotable water. Therefore, the first objective of this study was toidentify the factors, including raw water quality and treatment processparameters, which cause effective (and ineffective) arsenic removal atwater treatment plants. Arsenic in groundwater occurs in two oxidationstates, As(III) (arsenite) and As(V) (arsenate). Since the removal ofarsenic depends on its speciation, determining which species are presentin the water is crucial. It is of paramount importance to convert allarsenic species in the ground water to As(V) before any treatment forarsenic removal. In the most treated waters As(V) accounted for almost100% of the dissolved arsenic. Oxidation is clearly inadequate, ifresultant water contains any As(III), and higher degree of oxidationshould lead to improved arsenic removal overall. Many authors have shownthat conversion between the inorganic forms of arsenic As(III) and As(V)is likely. There is no universally accepted method for preserving Asspecies in water samples. Field separation was investigated as a mean ofeliminating the need for preservation. Using small ion exchangecartridges in the field has proven to be a reliable method of separatingarsenic species. Once separated, the fractions with the differentspecies are analyzed in a good equipped analytical laboratory.