Technologies and Costs for Removal of Arsenic From Drinking Water

TABLE 2-11Arsenic Removal with RO at Pilot-ScaleMembrane Water Type Charge AsSpeciesAsRejectionSingle ElementTFCL-HRHigh DOC GW ( - ) Total As >90%Low DOC GW ( - ) Total As >80%RO 1 Finished SW NARO 2 Finished SW NARO 3 Finished SW NARO 4 Finished SW NANA: Not AvailableV >95%III 60%V >95%III 75%V >95%III 68%V >95%III 85%Overall, RO is capable of achieving finished water arsenic concentrations below 0.002 mg/Lwhen arsenic is present as As(V). As(III) rejection is not as significant, however, conversion toAs(V) can be achieved with pre-oxidation.2.5.8 Electrodialysis ReversalElectrodialysis (ED) is a process in which ions are transferred through membranes that areselectively permeable towards cations or anions under the influence of direct electric current. Theseparation mechanism is actually an ion exchange process. The ions travel from a lesser to a higherconcentrated solution. In this process, the membranes are arranged in an array or stack placedbetween opposite electrodes, with alternating cation and anion exchange membranes. The mobilityof the cations or anions is restricted to the direction of the attracting electrodes, and this results inalternating sets of compartments containing water with low and high concentrations of the ions. Theelectrodialysis reversal (EDR) process is an ED process with periodic reversal of the direction oftravel of the ions caused by reversing the polarity of the electrodes. The advantage of polarity2-40