AWWA WQTC65873

Removal of groundwater contaminants, including arsenic, perchlorate, and total dissolved solids (TDS) in a high-silica groundwater using electrodialysis reversal (EDR) was evaluated. Pilot study results showed EDR as a viable treatment alternative for the Magna Water Company's (MWC) groundwater supply. Removal of perchlorate from the EDR concentrate using biofiltration was also evaluated. The MWC provides potable water to approximately 28,000 customers in the northwest section of Salt Lake County, Utah. MWC water comes from two sources: groundwater from the Barton and Haynes Wellfields; and, treated surface water purchased from a neighboring water district. Groundwater contains arsenic ranging from 8 to 18 ug/L; TDS from 770 to 1350 mg/L; and silica near 70 mg/L. Perchlorate has been measured at 14 ug/L in Barton Well No. 5 (BW5) and is expected to impact additional wells in the near future. Perchlorate was first detected in BW5 in 1997. A six-month pilot study conducted in 1999 and 2000 determined that EDR was a viable treatment alternative for perchlorate removal and showed promise in removing arsenic. Studies in 2001 through 2003 evaluated separate treatment alternatives of perchlorate and arsenic. A second pilot study conducted in 2004 and 2005 confirmed the use of EDR for multicontaminant removal. The study showed that a two-stage EDR system removed perchlorate to less than 4 ug/L at feed concentrations of 10 and 25 ug/L. A four-stage system removed perchlorate to less than 4 ug/L at feed concentrations of 50 to 60 ug/L. At arsenic feed concentrations of 10 ug/L, two-stage operation removed arsenic to less than 2 ug/L. The percent removal of TDS was near 88 percent throughout piloting. Silica levels remained constant in feed and treated water, indicating silica was not impacting treatment. Removal of perchlorate from the EDR concentrate stream prior to discharge was also evaluated using an innovative biological treatment process (BIOBROx). 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 to 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 simultaneous removal of arsenic, perchlorate, and TDS by EDR, followed by the biodestruction of perchlorate in the concentrate stream represents a unique approach to a complex water quality problem. Design of the full-scale EDR treatment system and biofiltration system was completed in May 2007 and construction began in June 2007. This paper details arsenic, perchlorate, and TDS removal results from the 2005 to 2005 pilot study and describes the design approach used in full-scale implementation. Includes tables, figures.