Technologies and Costs for Removal of Arsenic From Drinking Water

APPENDIX E: BASIS FOR REVISED ANION EXCHANGE COSTSE.1 OVERVIEWTwo sets of costs were developed for anion exchange - one where the sulfate concentrationis less than or equal to 20 mg/L and the other where sulfate is greater than 20 mg/L, but less than orequal to 50 mg/L. The costs in both the April 1999 Technology and Cost Document (1) and theNovember 1999 Technology and Cost Document (2) utilize models based on nitrate removal. TheWater Model (3) was one of the cost models used for small systems with design flows less than 1mgd. Sulfate concentrations for this model were between 50 and 100 mg/L. The November 1999Technology and Cost Document listed the design criteria for large systems (> 1 mgd) using the W/Wmodel. The sulfate concentration was 80 mg/L and the nitrate concentration was 100 mg/L. It wasnot possible to modify the sulfate concentration in either of these two models. It was determined thatthe existing cost models could not be used to estimate costs for anion exchange options with sulfateat or below 50 mg/L. A similar summary to this was prepared for the disposable activated aluminacosts used in the proposed and final rules.E.2 DESIGN ASSUMPTIONS AND BASISE.2.1Capital Costs1. Empty Bed Contact Time (EBCT) = 2.5 minutes per columnBasis. The designs in the November 1999 Technology and Cost Document were based on anEBCT of 2.5 minutes. Case study costs in the AwwaRF report (4) were based on EBCTs of1.5 minutes. The EBCTs for two full-scale anion exchange plants removing arsenic were 3.7minutes for Plant A and 5.6 minutes for Plant B (5).E-1