AWWA MTC61191

The Governor of Texas created an initiative for the evaluation of the feasibility of seawater desalination to provide additional water supply. Under this initiative, three projects were created that were administered by the Texas Water Development Board (TWDB). The City of Corpus Christi secured a grant for one of the three projects, a "Large Scale Desalination Demonstration Project Feasibility Study". The required product water flow-rate of the project was 25-mgd. However, in order to produce 25-mgd of finished water, a larger portion of raw water is required to account for waste streams for the pretreatment and the reverse osmosis system, itself. While there were many facets to the investigation, a major focus was to identify potential treatment methods to produce potable water for the region. Therefore, an evaluation of source water issues and treatment alternatives, as well as preparation of design criteria, plant and space requirements, and estimated capital and operations and maintenance costs for a conceptual desalination facility was performed. Several areas were identified for potential seawater supply, including several industrial sites, a power plant intake, and other areas along the coast. Challenges were realized due to hypersaline conditions in many areas, which can increase the cost of potable water production. Therefore, a thorough review of source water options as well as the potential for groundwater blending was examined. The variation in source waters and blending impacted design criteria such as salinity, temperature, and pretreatment requirements. The proposed RO system consists of two passes. In the second pass, the brine or concentrate in the first stage feeds the second stage. The concentrate quality from the second stage is better than the raw feed quality, so it is directed back to the feed, upstream of the RO feed pump. This two-pass configuration uses the least amount of energy while projecting water quality that was consistently below the established maximum water quality limits at temperatures ranging from 10 to 30 degrees Celsius. This paper provides a brief background on the project, looks at project goals, reviews raw water quality and finished water quality goals, and looks at the reverse osmosis desalination design criteria to meet project objectives. Includes 3 references, table, figures.