The Fort Bend Subsidence District (FBSD) adopted a regulatory plan in 2003 to establish a policy for groundwater use regulation to control subsidence on a regional basis. Per the FBSD 2003 regulatory plan, the City of Sugar Land (City) must reduce and maintain its groundwater use by 30 percent in 2013 and 60 percent in 2025. To meet the required 30 percent conversion by 2013, the City plans to construct a 9 mgd surface water treatment plant, which will be expanded to an ultimate capacity of 22 mgd. The Brazos River water delivered through Oyster Creek will be the source water for Sugar Land's SWTP. The City evaluated several treatment process alternatives and selected to build a membrane treatment plant with high-rate clarification for pretreatment and granular activated carbon (GAC) for taste and odor (T&O) control. A 30-day pilot testing was conducted using a high rate clarifier with plate settlers at a planemetric surface overflow rate (SOR) of 2.5 gpm/sf converting to a projected plate SOR of 0.33 gpm/sf and was able to produce settled water turbidity less than 2 NTU 95% of the time, meeting the State requirement of obtaining 2-log virus removal credits from the pretreatment process. Pilot testing was conducted with pre-oxidant chlorine dioxide dosed at 0.4 mg/L and coagulant polyaluminum chloride (PAC1) dosed at 40-100 mg/L. PAC1 was able to achieve 40-50% TOC removal. The application of the high rate clarification with plates as low pressure membrane pretreatment was successfully and produces good settled water quality to the membrane system for the Sugar land SWTP. The implementation of the high-rate plate clarifiers in the plant design reduces plant site footprint.
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