Technologies and Costs for Removal of Arsenic From Drinking Water

Small Systems (Less than 1 mgd)The Water Model was used to estimate capital and O&M costs for small C/F treatment plants.The following design criteria can be used in developing capital and O&M cost estimates:# Package plant for all small systems, filtration rate 5 gpm/ft 2 ;# Ferric chloride dose, 25 mg/L;# Polymer dose, 2 mg/L; and# Lime dose, 25 mg/L for pH adjustment.Large Systems (Greater Than 1 mgd)The W/W Cost model can be used to develop capital and O&M cost estimates for large C/Fplants. The following design criteria can be used to estimate capital and O&M costs:# Ferric chloride dose, 25 mg/L;# Polymer dose, 2 mg/L;# Lime dose, 25 mg/L for pH adjustment;# Rapid mix, 1 minute;# Flocculation, 20 minutes;# Sedimentation, 1000 gpd/ft 2 using rectangular tanks; and# Dual media gravity filters, 5 gpm/ft 2 .3.6.2 Enhanced CoagulationEnhanced coagulation involves modifications to the typical C/F process such as increasing thecoagulant dosage, reducing the pH, or both. The process is nearly identical to that of conventional C/Fwith those two exceptions. Source waters with high influent As(III) concentrations may require preoxidationfor conversion of arsenite to arsenate (see Section 3.5).For the purpose of estimating costs, it was assumed that a typical C/F treatment plant couldremove 50 percent of the influent arsenic prior to enhancement. It was also assumed that the onlyadded O&M burden would result from power and materials costs, no additional labor was assumedto be required. Costs presented are for the enhancement only, and are in addition to any currentannual debt incurred by the utility.Small Systems (Less than 1 mgd)The VSS Model makes no appropriations for estimating enhanced coagulation capital andO&M costs. As a result, the Water Model was used to estimate capital and O&M costs for all3-24