Technologies and Costs for Removal of Arsenic From Drinking Water

quality feed stream and often requires substantial pretreatment to remove suspended solids and otherfoulants. RO also often requires pH adjustment after the membrane process and may require theaddition of an anti-scalant before the membrane process. For the purpose of this analysis, costs werenot provided for a substantial pre-treatment system, other than the anti-scalant system. RO has thebenefit of greater arsenic removal compared to low-pressure membrane processes, but is typicallyassociated with higher capital and O&M costs. Costs are not provided for RO because other optionsare more cost effective and have much smaller waste streams. RO may be cost effective if removalof other contaminants is needed and water quantity is not a concern.Both the VSS Model and the W/W Cost Model included cost estimation for RO. Since theW/W Cost Model was assembled, however, RO spiral-wound membrane module costs havedecreased by approximately 50 percent. For this reason, the membrane module portion of the capitalcosts can be reduced by 50 percent. The membrane replacement portion of the O&M costs can alsobe reduced by 50 percent to account for reductions in membrane costs. The W/W Cost Model for ROwas only valid up to a capacity of 200 mgd. The model also makes an assumption that recovery is 80percent for systems of 1 to 10 mgd, and 85 percent for systems larger than 10 mgd.3.10 GREENSAND FILTRATIONGreensand filtration is an oxidation filtration process that has demonstrated effectiveness forthe removal of arsenic. The greensand filtration medium is produced by treating glauconite sand withKMnO 4 until the granular material (sand) is coated with a layer of manganese oxides, particularlymanganese dioxide. Arsenic compounds displace species from the manganese oxide (presumably OH -and H 2 O), becoming bound to the greensand surface - in effect an exchange of ions. The oxidativenature of the manganese surface converts As(III) to As(V), and As(V) is adsorbed to the surface.The VSS model was used for estimating greensand filtration capital and O&M costs.Greensand filtration costs were not included in either the Water Model or the W/W Model. Thistechnology is considered to be a small systems technology and as a result costs were not estimated forlarger systems. This technology could be effectively operated in larger system sizes, but cost data arenot readily available. The key parameter is the ratio of source water iron and arsenic. If high3-57