Technologies and Costs for Removal of Arsenic From Drinking Water

The source water at Plant D has the following critical characteristics:ParameterArsenic (total)Average Source Water Results59.0 Fg/LpH 8.3Alkalinity 55.5 mg/L CaCO 3FluorideSulfate1.13 mg/L15 mg/LThe roughing tank treated 5,200 BV of water before breakthrough (effluent = influent). Thearsenic concentration in the effluent from the second tank was less than 2 Fg/L as it wasthroughout the run. Arsenic concentration was the only key parameter that varied to any extentduring the testing. The run length would be affected by pH and by the influent arsenicconcentration. The pH was consistent and represents the upper bound on the range ofapplicability for this cost equation. A run length of 5,200 BV was used as the run length forthe range of 8 # pH # 8.3. Since influent arsenic concentrations for most systems affected bythe rule should be much lower than 59 Fg/L, this should be a very conservative run length forsystems with lower arsenic concentrations and/or pH values at the lower end of the range.The effluent pH and effluent concentrations of alkalinity, fluoride and sulfate indicated almostno change from their value in the influent. Thus, the existing corrosion control should besufficient.The previous approach described in Appendix G of the November 1999 Technology and CostDocument (1) relied upon pilot-scale data from Severn-Trent (11). The study examinedarsenic removal over a pH range from pH 6 to pH 7.5 in a single column. The three runlengths derived from that data ranged from 16,500 BV and pH 7 to 3,000 BV at pH 8 for 10%breakthrough in a single column. Actual run lengths to 50% breakthrough in that study fornatural pH 7.5 ranged from 9,400 to 13,000 BV based on mesh size. The data from the twofull-scale facilities (3) indicated that the roughing column could be operated almost completebreakthrough (effluent = influent) before concentrations in the effluent of the second columnexceeded 5% of the influent concentration. This data also indicates that a natural pH runD-13