Technologies and Costs for Removal of Arsenic From Drinking Water

equates to a total (municipal and industrial) influent concentration of around 13 Fg/L (AWWARF,1998). As a result, if a water system is located in an area that has a background arsenic concentrationnear 13 Fg/L, it may not be permitted to discharge to the local POTW. There are several problemswith the above example. The first is that the background concentration would be reduced becausearsenic is being removed from drinking water. Therefore, the TBLL would need to be revised. Thesecond is that 41 mg/kg is being used as the upper limit for land application when the actual upperlimit is based on 75 mg As/kg biosolids since arsenic accumulation is unlikely to exceed the lifetimelimit. The key variables to determine if arsenic in the POTW biosolids would exceed the landapplication limit are: existing background arsenic concentration, water loss between drinking watertreatment plant and POTW, arsenic removal efficiency of the POTW, and the volume of biosolidsgenerated by the POTW. Land application restrictions on the biosolids would only likely be an issuewhen background arsenic levels are high, water loss is 50% or higher between the drinking watertreatment plant and the POTW, the POTW has a high arsenic removal efficiency and only generatesa low volume of biosolids. Thus, arsenic accumulation in biosolids is unlikely to be as significanta restriction as total dissolved solids (TDS) increases due to the salt used for regeneration for anionexchange.Anion exchange is regenerated using sodium chloride. Typical regenerations will use 10.2lb/cubic feet of resin. Even though the brine stream is small in volume, the TDS concentration of thebrine stream will be very high. As a result, the POTW discharge may increase the TDS content of thereceiving waters. Areas of the country with high TDS naturally or limited quantities of water may findany increase in TDS to be unacceptable. In areas where small increases in TDS can beaccommodated, the water loss between the drinking water treatment plant and the POTW and the sizeof the brine stream compared to the total volume of water treated at the POTW will affect themagnitude of the TDS increase.As with direct discharge, the primary cost associated with indirect discharge is that of thepiping. Accommodations must also 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. Other costs associatedwith indirect discharge may include lift stations, additional piping for access to the sewer system, orother surcharges to accommodate the increased demands placed on the local POTW.4-8