AWWA ACE65166

The Magna Water Company (MWC) provides potable water to approximately 28,000 customers in the northwest section of Salt Lake County. Their water comes from two sources: groundwater from the Barton and Haynes Wellfields; and, treated surface water purchased from a neighboring water district. The groundwater contains arsenic ranging from 8 to 18 µg/L; total dissolved solids (TDS) from 770 to 1350 mg/L; and silica near 70 mg/L. Perchlorate has been measured at 14 µg/L in Barton Well No. 5 (BW5) and is likely to impact additional wells in the near future. Perchlorate was first detected in 1997. A six-month pilot study conducted in 1999-2000 determined that electrodialysis reversal (EDR) was a viable treatment alternative for perchlorate and showed promise in removing arsenic. However, at that time, arsenic removal was not fully evaluated. Studies in 2001-2003 evaluated separate treatment of perchlorate and arsenic. It was determined that a single technology addressing perchlorate, arsenic, and TDS would reduce costs. A second pilot study conducted in 2004-2005 confirmed the use of EDR for multi-contaminant removal. This pilot study showed that a two-stage EDR system removed perchlorate to less than 4 µg/L at feed concentrations of 10 and 25 µg/L. A four-stage system removed perchlorate to less than 4 µg/L at feed concentrations of 50 to 60 µg/L. At arsenic feed concentrations of 10 µg/L, 2- stage operation removed arsenic to less than 2 µg/L. The percent removal of TDS was near 88% throughout piloting. Silica levels remained constant in feed and treated water, indicating silica was not impacting treatment. Another treatment objective identified by the MWC was to remove perchlorate from the EDR concentrate stream prior to discharge. To that end, an innovative biological treatment process (BIOBROx) was developed and piloted in conjunction with the EDR pilot testing. EDR concentrate was blended with municipal wastewater and treated in a fixed-bed bioreactor. Piloting showed sustained, complete perchlorate destruction at a 10-minute empty-bed contact time without the addition of an exogenous carbon source or nutrients. Alternative biological processes require 6-24 hours of contact time and high concentrations of ethanol or acetic acid to achieve the same perchlorate removal results in a concentrate stream. The design of the EDR and BIOBROx facilities was completed in April 2007. Construction will begin in mid 2007. The simultaneous removal of arsenic, perchlorate, and TDS by EDR, followed by the biodestruction of perchlorate in the concentrate represents a unique approach to a complex water quality problem. This paper details arsenic, perchlorate, and TDS removal results from the various pilot studies, and describes the design approach used in full-scale implementation.