At Tri-County, located in Riesel TX, there are two plants which produce a combined flow rate of 500 gpm. Plant #6 produces 250 gpm while the remote plant #13 also produces 250 gpm. The average temperature of water for both plants are between 147° F and 150° F. Both plants have an induced draft type cooling tower system. The raw water at Tri-County plants has high concentrations of arsenic and iron. Once the temperature of the water is reduced with the aid of the cooling towers, the water is stored into the existing GSTs. Due to filter issues arsenic removal was not efficient and the client avoided using water from Plant # 13, which had higher arsenic concentration. Additionally, the cooling towers were having plugging problems due to the insoluble iron and manganese precipitates. A pilot study was performed by WETS to improve the arsenic filtration system and to address the cooling tower fouling. The first round of pilot study was conducted on Plant #6 (Well #4). The pilot study used a small-scale version of a gravity filter system which utilizes Greensand Plus and anthracite. Greensand plus has the capability to absorb arsenic because of its manganese dioxide coating. The pilot study was performed using raw water without any orthophosphate. An aeration water treatment system was used to mimic the effect of the cooling tower for oxidizing the iron and manganese elements and filtration was used to filter out the precipitates. Another sample of water was taken from the GST which had gone through the cooling tower and contained orthophosphate. This sample was not routed through the aerator and was directly injected into the pilot filter. It was determined that Greensand Plus was extremely effective at reducing the arsenic concentration well below the TCEQ limit. The pilot study arrangement included pilot aerator with blower, pilot translucent filters, static mixers, metering pumps, piping assemblies and hoses. Aeration process was used to oxidize iron and manganese particles. The gravity filtration system used dual media with Greensand plus and anthracite to filter out the iron and manganese precipitates. A hose bibb was used to transfer water from the well pump discharge to the pilot study equipment. Bleach was added to the raw water to allow for chlorine activation of the Greensand plus media. The metering pumps were used to inject the chlorine solution through the injection quills into the main pilot water line from the hose bibb. Based on the successful completion of the pilot study, WETS recommended Tri-County to rehab the existing filters to utilize Greensand plus and anthracite, to retain the orthophosphate dosing to avoid plugging of cooling towers, add chlorine dosing to activate the effect of Greensand plus media, valve repair, and adding a sludge tank for backwash purposes.
Client : Tri County SUD – Riesel, TX
Year : 2021
Category : Pilot Study