Technologies and Costs for Removal of Arsenic From Drinking Water
Technologies and Costs for Removal of Arsenic From Drinking Water
Technologies and Costs for Removal of Arsenic From Drinking Water
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water characteristics must be considered when evaluating POE <strong>and</strong> POU devices <strong>for</strong> arsenic removal.To be effective these devices should work with minimal attention <strong>and</strong> be relatively inexpensive <strong>for</strong>the user. Reverse osmosis, activated alumina, <strong>and</strong> ion exchange are three treatment techniques thathave been evaluated <strong>and</strong> shown to be effective. This chapter looks at the removals achieved by each<strong>of</strong> these three treatment techniques, <strong>and</strong> presents total costs <strong>for</strong> each treatment option.5.2 VARIABLES AFFECTING REMOVAL EFFICIENCY5.2.1 Speciation<strong>Arsenic</strong> speciation is critical to the removal efficiency <strong>of</strong> every technology presented in thisdocument. As previously discussed, inorganic arsenic occurs in two primary <strong>for</strong>ms, arsenite (AsIII)<strong>and</strong> arsenate (AsV). Arsenite is removed less efficiently because it predominantly occurs in theuncharged (H 3 AsO 3 ) state in source waters with a pH <strong>of</strong> less than 9.0. The dominant arsenate <strong>for</strong>ms2-are anionic species, H 2 AsO 4 <strong>and</strong> HAsO 4- . Identification <strong>of</strong> the ionic <strong>for</strong>m <strong>of</strong> arsenic is necessary <strong>for</strong>selection <strong>and</strong> design <strong>of</strong> a removal process. All technologies discussed in this document removearsenate more effectively than arsenite. There<strong>for</strong>e, if arsenite is the predominant species present,oxidation to arsenate may be required to achieve the desired removal.5.2.2 pHAs previously stated, pH plays a significant role in determining the removal efficiency <strong>of</strong> aparticular technology. Most processes are relatively unaffected by pH in the range <strong>of</strong> 6.5 to 9.0.However, activated alumina studies have shown the optimum pH <strong>for</strong> arsenic removal to be between5.5 <strong>and</strong> 6.0, <strong>and</strong> reverse osmosis processes may require pH adjustment to prevent precipitation <strong>of</strong>salts on the membrane surface.5.2.3 Co-occurrenceCo-occurrence <strong>of</strong> inorganic contaminants, such as sulfate <strong>and</strong> silica, as well as suspendedsolids, can cause interference with arsenic removal. Sulfate is preferentially adsorbed relative toarsenic by ion exchange processes. This preference can result in another phenomenon known as5-2
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