Technologies and Costs for Removal of Arsenic From Drinking Water

The costs in both the April 1999 Technology and Cost Document (1) and the November 1999Technology and Cost Document (2) utilize models based on nitrate removal. The Water Model wasone of the cost models used for small systems with design flows less than 1 mgd. Sulfateconcentrations for this model were between 50 and 100 mg/L. The November 1999 Technology andCost Document listed the design criteria for large systems (> 1 mgd) using the W/W model. Thesulfate concentration was 80 mg/L and the nitrate concentration was 100 mg/L. It was not possibleto modify the sulfate concentration in either of these two models. It was determined that the existingcost models could not be used to estimate costs for anion exchange options with sulfate at or below50 mg/L.Design Assumptions: Capital CostsThe following assumptions were made to estimate the capital cost of anion exchange. Thebasis for these assumptions are provided in Appendix E.1. Empty Bed Contact Time (EBCT) = 2.5 minutes per column2. The estimated cost of the anion exchange resin was $125/ft 3 for all system sizes.3. The bed depth assumption ranged from 3 feet to 6 feet depending upon the design flow. Themaximum diameter per column was 12 feet. When the calculated media volume exceeded themaximum, the treatment media was divided into several beds to maintain a realistic beddiameter. Thus, larger designs include multiple anion exchange columns, each treating aportion of the total flow.4. The vessel cost has been sized based on 50% bed expansion during backwash. The vesselvolume was calculated as (1.5)(media volume).5. The vessel cost is based on the following equation:Cost = 63.288 * (Vessel Volume in gallons) ^ 0.6793-48