Deep Media Filter Piloting to Enhance Capacity and Perormance

The Village Creek Water Reclamation Facility (VCWRF), a 166 MGD average daily flow facility, is currently the sole wastewater treatment plant for City of Fort Worth. It is a conventional plant with headworks, primary treatment, activated sludge secondary treatment, filters, and chlorine disinfection.Filtration is employed at the VCWRF as a tertiary treatment process for reduction of total suspended solids (TSS), related biochemical oxygen demand (BOD), and turbidity. The VCWRF has two filtration trains. Filters 1-20 are deep bed granular dual-media filters and Filters 21-32 are dual-media traveling bridge filters. This project is focused on the deep bed Filters 1-20. The VCWRF maintains a Type I Reuse permit from the Texas Commission on Environmental Quality (TCEQ), allowing use of effluent from the deep media filters for the City's reuse program. The permit carries a turbidity limit of 3 NTU.The deep media filters have been in operation since the mid-1970s and are currently limited to a nominal capacity of 120 MGD, averaging around 3.8 gallons per minute per square foot (gpm/sf) of filter area. Demand for reuse water has increased, creating a need for increased flowrates with reliable effluent quality and longer filter run times. In addition, flows into VCWRF are increasing and significant capital savings could be achieved by uprating the existing filters rather than expanding with new filters. Piloting was initiated as a first step to evaluate various alternatives for improving the performance and capacity of these 20 filters at the VCWRF.Freese and Nichols, Inc. (FNI) and CDM Smith (CDMS) were retained by the City to evaluate alternatives and design improvements to the filter complex. The team conducted filter pilot studies to aid in the selection of media that could maximize filter capacity and meet the TCEQ Chapter 210 Type I reuse water quality requirements. Pilot units from two filter manufacturers were used to test different media configurations and depths of three media types: mono-media sand, mono-media anthracite, and dual-media sand/anthracite. Media sizes ranged from 1.5 mm to 3.0 mm. The tested loading rates ranged from 4 to 9 gpm/sf.The filter pilot study was conducted to optimize the media type and size for these filters. The primary objectives of the filter piloting were to:• Determine the optimal media configuration and size to maintain an effluent turbidity consistently less than 3 NTU;• Increase filter run time from a current average run time of 14 hours; and• Increase filter hydraulic loading rate above the current 4 gpm/sf rating.Results from the pilot study indicated the potential for substantial uprating of the filtration capacity, consistent compliance with reuse turbidity standards, and avoidance of large future capital outlays for filter expansion.This paper presents results from the pilot testing and media selection; overall layouts of the major components of the pilot systems; lessons learned during the start-up and operation of pilot systems; and how results were used to select the final design alternative and operational criteria for the deep filter rehabilitation at the VCWRF.