AWWA ACE59976

For many utilities waste management dictates treatment selection, as was the case for one Tribe in Nevada faced with complying with the revised arsenic (As) maximum contaminant level (MCL) of 10 µg/L. For this Tribe, treatment selection was not as simple as which process reliably removed arsenic below the MCL for the least cost, but how to manage the residuals generated from the treatment process. The Tribe explored multiple treatment processes through the Arsenic Removal Technology Pilot Plant Study. The study included an assessment of coagulation/microfiltration, coagulation/direct filtration, ion exchange (IX), and three adsorptive medias at both ambient and depressed pH. Due to challenging water quality characteristics including high arsenic levels (70 and 110 µg/L), significant levels of silica (55 mg/L) and an elevated pH, only the IX and coagulation/microfiltration (C/MF) process were capable of consistently removing arsenic below the MCL. Additionally, these technologies were estimated to have similar life cycle costs, +/- 10%, assuming all waste generated would be classified as non-hazardous. With As concentrations as high as 10,000 µg/L in the waste brine, the IX process would potentially leave the Tribe with a hazardous waste management program for compliance with federal regulations under 40 CFR and/or possibly be classified as a hazardous waste RCRA facility. In addition to the liability associated with managing hazardous waste and a decrease in public acceptance, the additional costs to dispose of the hazardous waste would increase the life cycle cost of the Tribe's facility by 20 percent. So, while the water treatment process proved uncomplicated and reliable, the waste treatment would potentially be costly and require additional permits to operate the facility. On the other hand, research on C/MF sludge has indicated that the dried sludge from the C/MF would pass the TCLP test and could be disposed of in a municipal, non-hazardous landfill with fewer regulatory compliance issues and for a significantly lower disposal cost. In the end, it was not the water treatment life cycle treatment cost or reliability that dictated the appropriate technology, but the management of the As laden waste. The Tribe selected C/MF to provide their people with affordable and safe water with an easy to manage waste residual. Includes 4 references.