Technologies and Costs for Removal of Arsenic From Drinking Water

EPA has established water quality criteria under authority of the Clean Water Act. For watersused for fish consumption, the ambient water quality criterion for arsenic was set at 0.14 Fg/L. If awater source is also used as a source of drinking water, the arsenic limit is reduced to 0.0175 Fg/L;although some States use the drinking water MCL for this purpose. These criteria are used by stateregulatory agencies as a basis for the determination of discharge limits for arsenic depending on theclassification of the receiving water. 1 The allowable discharge is therefore affected by the ability ofthe receiving water to assimilate the arsenic without exceeding the water quality criteria.The primary cost associated with direct discharge is that of purchasing and installing thenecessary piping. Accommodations must be made for washout ports to prevent clogging because ofsedimentation in pipelines. Valving is necessary to control waste flow in the event of pipe bursts, andpipe must be laid at a sufficient depth to prevent freezing in winter months. Direct discharge requireslittle oversight, and operator experience and maintenance requirements are minimal. This method hasbeen used successfully to dispose of alum and lime sludges, as well as brine streams generated bysystems using RO and IX (DPRA, 1993a).4.3.2 Indirect DischargeIn some cases, water treatment process sludges, slurries, and brines may be discharged to aPOTW. This most often occurs when the treatment plant and POTW are under the same managementauthority. This disposal option may require the installation of a conveyance system (i.e., piping) toaccess the sanitary sewer if an adequate system is not already in place (DPRA, 1993a).Indirect discharge is a commonly-used method of disposal for filter backwash and brine wastestreams. Coagulation/filtration and LS sludges have also been successfully disposed of in this manner.However, the POTW receiving such wastes must be able to handle the increased hydraulic and solidsloading. The capacity of the sewer system must also be considered when selecting indirect dischargeas a disposal option.The residuals generated from an arsenic treatment process may be classified as an industrialwaste since they contain contaminants, namely arsenic, which may impact the quality of the sludgesgenerated by the POTW. As a result, discharge to a POTW is only acceptable when arsenicconcentrations fall within the Technically Based Local Limits (TBLL) established by the POTW under1 Note that State and local limits may be more stringent than federal limits for specific contaminants,including arsenic.4-6