Missouri City Surface Water Treatment Plant
To meet the challenge of regional subsidence and new regulations restricting groundwater production, the City of Missouri City, Texas, determined to build a new surface-water treatment plant. Designed by HDR, in association with Enprotec/Hibbs & Todd, Inc. (eHT), the new plant's initial production capacity is 10 million gallons per day. As a long-term cost saving measure, the plant was designed and constructed with adequate space to accommodate the equipment necessary to easily double the capacity in the future. Planned phases include an expansion to 20 mgd in 2017 and an ultimate capacity of 33.5 mgd in 2025.
Because water quality from the Brazos River is extremely susceptible to change, the treatment processes needed to be robust and flexible. To meet these requirements, plate settlers were selected for pretreatment, and low pressure membranes were selected to meet filtration needs. Both of these processes were pilot tested for four months before plant design began. As expected, the river's flow and water quality were highly variable during the testing period, allowing a comprehensive evaluation of the treatment processes. The pilot testing confirmed that the selected processes would provide high quality water under all anticipated conditions. Aluminum chlorohydrate (ACH) was the selected coagulant. Although more expensive than other coagulants on a per pound basis, the selection of ACH proved to be cost effective due to its superior treatment performance and substantially lower required dosage. Other advantages of ACH include superior removal of total organic carbon (TOC), reduced alkalinity consumption, and reduced demand for other required treatment chemicals.
The Missouri City Surface Water Treatment Plant is an excellent example of long-term low-cost solution provided through conscientious effort to keep costs down without sacrificing quality or performance. One of several plants treating water from the Brazos River and constructed around the same time in response to county subsidence regulations, the unit cost of the plant, at $3 per constructed gallon of capacity, was less than half that of the other plants.