AWWA ACE65166

The Magna Water Company (MWC) provides potable water to approximately 28,000 customersin the northwest section of Salt Lake County. Their water comes from two sources: groundwaterfrom the Barton and Haynes Wellfields; and, treated surface water purchased from a neighboringwater district. The groundwater contains arsenic ranging from 8 to 18 µg/L; total dissolved solids (TDS) from 770 to1350 mg/L; and silica near 70 mg/L. Perchlorate has been measured at 14 µg/L in Barton WellNo. 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 1999-2000determined that electrodialysis reversal (EDR) was a viable treatment alternative for perchlorate and showed promise inremoving arsenic. However, at that time, arsenic removal was not fully evaluated. Studies in2001-2003 evaluated separate treatment of perchlorate and arsenic. It was determined that asingle technology addressing perchlorate, arsenic, and TDS would reduce costs.A second pilot study conducted in 2004-2005 confirmed the use of EDR for multi-contaminantremoval. This pilot study showed that a two-stage EDR system removed perchlorate to less than4 µg/L at feed concentrations of 10 and 25 µg/L. A four-stage system removed perchlorate to lessthan 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 silicawas not impacting treatment.Another treatment objective identified by the MWC was to remove perchlorate from the EDRconcentrate stream prior to discharge. To that end, an innovative biological treatment process(BIOBROx) was developed and piloted in conjunction with the EDR pilot testing. EDRconcentrate was blended with municipal wastewater and treated in a fixed-bed bioreactor.Piloting showed sustained, complete perchlorate destruction at a 10-minute empty-bed contacttime without the addition of an exogenous carbon source or nutrients. Alternative biologicalprocesses require 6-24 hours of contact time and high concentrations of ethanol or acetic acid toachieve the same perchlorate removal results in a concentrate stream.The design of the EDR and BIOBROx facilities was completed in April 2007. Construction willbegin 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 toa complex water quality problem. This paper details arsenic, perchlorate, and TDS removalresults from the various pilot studies, and describes the design approach used in full-scaleimplementation.

Product Details

Edition:

Vol. - No.

Published:

06/01/2007

Number of Pages:

3

File Size:

1 file