Technologies and Costs for Removal of Arsenic From Drinking Water

carbonate hardness removal produces approximately twice the amount of solids per pound of hardnessremoved as the use of this process for non-carbonate hardness removal.Enhanced LS plants typically produce 1,000 to 8,000 pounds of solid per million gallons ofwater treated depending upon the hardness of the water (AWWARF, 1998). Arsenic concentrations,however, are generally lower than C/F sludges due to the increased volume of solids produced.Selection of Handling and Disposal OptionsTypical solids content of enhanced LS blowdown range from 1.0 to 4.0 percent, depending onraw water hardness. Gravity thickening may be used as a pretreatment for sludges prior to handlingby other mechanical or non-mechanical dewatering processes. Filter presses are capable of attainingfinal sludge solids contents in the range of 40 to 70 percent, while scroll centrifuges may achieve finalsolids contents of 65 to 70 percent. Evaporation ponds and storage lagoons may be suitable forsmaller treatment plants, but because they are land intensive may not be applicable for large watersystems.Land application of treatment sludges is a possible disposal alternative. As discussed insection 4.3.2, total arsenic cannot exceed 41 mg/kg if sludges are to be applied with no restrictions.Sludges with arsenic concentrations between 41 and 75 mg/kg may be land applied provided that thetotal loading does not exceed 41 kg per hectare.Sludges will require dewatering prior to landfill disposal. If the residuals pass the TCLP testthey may be disposed of in a sanitary landfill. Otherwise, residuals must be disposed of in ahazardous waste landfill. However, as with LS sludges, such treatment is not likely to be necessary,and should only be used as a last result.Tests conducted by the University of Colorado indicate that enhanced LS sludges will pass theTCLP test (AWWARF, 1998). Additional tests conducted by the University of Colorado confirmedthat the treatment sludge from enhanced LS treatment will typically pass the TCLP (results: 0.0009to 0.0284 mg/L; Amy, 1999). A case study presented by Sorg (2000) lends further strength to theexpectation that the residuals from this treatment process may be treated as nonhazardous.Sludge from the enhanced LS plant in a recent EPA study was collected, sent to a slurry tank,and then to a sludge lagoon (EPA, June 2000) . Approximately once every 2 years, or as required,the sludge lagoon was dewatered using an underdrain system. Arsenic was not detected in theleachate at any of the sampling locations used in the study (detection limit: 0.05 mg/L). As a result,4-17