APAI has had the opportunity to lead many projects at the City of Mansfield Bud Ervin Water Treatment Plant. These projects have included the design of two cast-in-place concrete clearwells (1 and 1.5 million gallons), a high service pump station to serve the City’s upper pressure plane, three expansions (two 10-MGD and one 15-MGD), and an uprating study for the sedimentation basins and gravity filters. The most recent expansion added a 15-MGD treatment train to the plant, and increased the overall treatment capacity to over 45 MGD. This expansion utilizes pressure membranes, followed by granular activated carbon contactors. The membrane system is unique in that it has been designed to treat either settled water from the existing conventional treatment system, or raw water in a direct filtration mode. This flexibility of operation allows the membranes to treat settled water for a majority of the time, which may increase the life of the membrane; however, during periods of high water demands, the membrane system can be switched to direct filtration of raw water. The direct filtration mode allows the plant to treat over 45 MGD of water at the facility. In addition to the membrane system, this expansion also includes two other advanced technologies.
Prior to this expansion, the plant utilized chlorine gas as part of the disinfection strategy. Since the plant is a neighbor to a middle school, neighborhood, and a church, the City elected to investigate switching from chlorine gas to an alternative method of chlorination. The evaluation, which included input from the City staff, led to the decision to switch from chlorine gas to an on-site generation sodium hypochlorite system. The other technology designed was the advanced oxidation process (AOP) system. The AOP system utilizes ultraviolet light and hydrogen peroxide to assist in treating the water for geosmin, a taste and odor compound.