(140d) Wilcox Aquifer Brackish Water Composition & Treatment Analysis

Fresh water is a rapidly diminishing essential resource. A major source of water in Texas comes from the Edwards and Wilcox aquifers. Groundwater usually needs to be treated before human consumption, to remove the dissolved solid content that leaches into the water as it sits in the aquifer. This paper has two goals: to characterize the brackish groundwater with data provided by San Antonio Water Systems (SAWS) and to verify the SAWS data and efficacy of a brackish water desalination pilot plant with inductively coupled plasma optical emission spectroscopy (ICP-OES) and pH measurements. A brackish water treatment system was designed, built, and analyzed for the purpose of treating brackish groundwater to EPA standards for potable water. The treatment process consists of four primary unit operations: carbon adsorption, ion exchange, RO, and ultraviolet (UV) disinfection. Valves and bypass loops were installed on the pilot plant in order to determine the effectiveness of each unit operating in isolation. Bacteria cultures derived from the residue of filtered 100 mL samples of raw water, (brackish water from the Wilcox aquifer) water treated with UV disinfection, and water treated without UV disinfection were used to determine the necessity and effectiveness of a disinfection unit. Raw water cultures revealed a significant amount of bacteria. Treatment without the UV disinfection removed 80% of the bacteria and treatment with UV disinfection removed 97.3% of the bacteria present in the water. Log of concentration vs pH diagrams generated from SAWS data determined the dominant species of the Wilcox aquifer groundwater to be bicarbonate (HCO3-1), sulfate (SO4-2), sodium (Na+1), chloride (Cl-1), calcium (Ca+2), magnesium (Mg+2), and potassium (K+1). Raw water treated by only the carbon adsorption unit, water treated only by the ion exchange unit, water treated only by the RO, and water treated by the entire system at varying operating pressures were analyzed by ICP-OES measurements to perform a more extensive analysis of the dissolved content. This analysis determined specific dissolved content of the raw water, verified the data from SAWS, the effectiveness of each unit operation, the effectiveness of the entire system, and the ideal operating pressure for the entire system. The initial total dissolved solids (TDS) of the feed water was 647.85 ppm. The carbon adsorption unit operating in isolation removed 13.47% of the original dissolved content, the ion exchange column operating in isolation removed 36.61% of the original dissolved content, and the RO unit operating in isolation at 450 psi removed 98% of the original TDS. Engaging the entire system with the RO unit operating at pressures of 150, 200 psi, 250 psi, 300 psi, and 450 psi all resulted in 98% removal of the original dissolved content, reducing the dissolved content for all four operating pressures to around 10 ppm TDS. The RO unit operating in isolation and the entire system operating at 150, 200, 250, 300, and 450 psi all reduced the dissolved content well below the Secondary EPA Standards for Drinking Water, making the treated water ideal for human consumption.