Mountain House

City of Denton, 
Texas

Water Reclamation Plant Design

Carollo provided a study, planning, design, and construction services for a new water reclamation facility to serve the Robson Ranch residential development located in Denton County, Texas. The project was designed with an initial capacity of 0.25 gpd, and planned for an ultimate capacity of 1.5 mgd. The initial planning study determined that the wastewater flow for the new development would be best handled by the construction of the new facility. Treatment processes for this facility include: above ground sequencing batch reactors (SBR); tertiary filtration; low-pressure ultraviolet (UV) disinfection; effluent reuse for golf irrigation; and dewatering by centrifuge.

During preliminary design, Carollo, along with the City of Denton, Robson Ranch Communities, Inc., and a contractor, investigated three types of UV disinfection. Low-pressure and high intensity UV lamps were evaluated, but due to the cycling of the flow, a low-intensity UV system was chosen to extend the lamp life. Effluent will be used for golf course irrigation and discharge to a surface stream where dechlorination normally is required.

Due to the low flows anticipated with a new development, a SBR was selected to provide a degree of flow equalization and storage, while still being capable of removing nitrogen, biochemical oxygen demand and suspended solids to levels required for surface discharge or reuse for irrigation. Tertiary filters (using a traveling backwash bridge) remove excess turbidity in the wastewater, which is followed by the low-pressure ultraviolet disinfection.

The waste activated sludge is pumped from the SBR to a sludge holding tank. A decanter removes the supernatant, and the thickened sludge is then processed through a centrifuge for dewatering. The centrifuge is designed so that the dewatered solids will meet a paint filter test, meeting the requirements for landfill disposal. The wastewater is designed to provide a high quality effluent, which will meet the water reuse standards for the State of Texas. Carollo also assisted in preparing Reuse and Texas Pollutant Discharge Elimination System (TPDES) permit applications.