Pilot Study of Brackish Groundwater Desalination Membranes
By Duane Bryant, and Meagan Brown
The San Antonio Water Systemﾒs (SAWS) Brackish Groundwater Desalination Program is designed as part of a strategy to meet San Antonioﾒs water needs over the next 50 years, while reducing dependency on more vulnerable water sources. The Texas Water Development Board has confirmed that a vast supply of brackish groundwater, more than 300 million acre-feet, exists in our region and has yet to be fully developed. According to the 2012 State Water Plan, which examines Texasﾒ projected water demands and resources through 2060, 3.5% of the new water supplies to be developed by 2060 will be provided by desalination (1). SAWS has elected to employ reverse osmosis (RO) membrane technology for desalination of brackish groundwater from the Wilcox Aquifer in South Bexar County, Texas. The Texas Commission on Environmental Quality (TCEQ) requires that all membranes be approved for use for each specific water source by providing historical qualification or pilot testing. SAWS began performing pilot testing in 2008 to confirm the performance of membranes from three different membrane manufacturers and, therefore, provide procurement and operational flexibility for the full-scale desalination facility. A consultant performed demonstration scale testing on one manufacturerﾒs membrane, and SAWS performed testing on the other two with in-house staff. SAWS primary goals in the pilot testing effort were to obtain a TCEQ capacity rating and approval of the use of membranes from three manufacturers for the full-scale facility and to evaluate certain pre-membrane processes. However, SAWS derived additional benefits from the piloting work. Analysis of the pilot testing results enabled SAWS to form some conclusions towards performance variances among manufacturers. The pilot study also produced unanticipated results in the clean-in-place (CIP) performance on the membranes of two manufacturers that merited additional testing and scrutiny.
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