Technologies and Costs for Removal of Arsenic From Drinking Water

TABLE 2-10Arsenic Removal with RO at Bench-ScaleMembrane MWCO Source Water Speciation pH As RejectionSingle ElementDK2540F 180 Deionized V 6.8 96%DK2540F 180 Lake Water V 6.9 96%DK2540F 180 Deionized III 6.8 5%DK2540F 180 Lake Water III 6.8 5%Flat SheetDK2540F 180 Deionized V 88%These results indicate very high rejection for As(V) but very low rejection for As(III) atneutral pH. Again, this points to the fact that oxidation conditions would be desirable, and that surfacecharge/electrostatic repulsion probably plays a role in arsenic rejection. Also, flat sheet testingproduced a rejection rate comparable, and slightly conservative, to the single element rejection rate.Several RO pilot-scale tests were also performed (AWWARF, 1998). Two tests wereperformed on high- and low-DOC groundwaters. Another set of tests was performed on spiked,finished surface water. The results from these pilot tests are summarized in Table 2-11.Table 2-11 shows substantial rejection for both the low- and high-DOC waters. Rejection wasonly slightly higher with the high DOC water. As with UF and NF, flux and recovery changes did notseem to affect arsenic rejection. Results for the four membranes tested on spiked finished water alsoshowed substantial removal. For all membranes during this test, As(V) exceeded 95 percent,however, As(III) rejection averaged only 74 percent.2-39