Design and First-Year Operation of the 50 mgd Membrane Treatment Facility at Gwinnett County, Georgia

摘要

Gwinnett County, located near Atlanta, Georgia, is one of the fastest growing counties in the nation. A new 20 mgd state-of-the-art water reclamation and processing facility, called the F. Wayne Hill Water Resources Center, became operational in December 2000 and now has been expanded increasing its capacity to 60 mgd (maximum month flow basis). The expanded plant produces high-quality water which discharges to the Chattahoochee River downstream of Lake Lanier. When construction of the new discharge line and outfall to Lake Lanier is completed and operational, the treated product water will discharge directly to the lake – the County’s raw water supply source. The NPDES permit for the lake discharge requires the monthly average total phosphorus, ammonia-nitrogen, and turbidity to not exceed 0.08 mg/L P, 0.4 mg/L NH3-N, and 0.5 NTU, respectively. After an extensive 1-year testing period in 2001 and an evaluation of performance, cost, and other factors, membrane filtration using ultrafiltration was selected as part of the advanced treatment processes to treat secondary effluent. The Zenon ZW-500c membrane process was the highest-ranked proposal following a selection process in 2002 that evaluated eight different membrane filtration systems from five manufacturers. Biological processes at the existing (Phase 1) plant were designed for complete nitrification, partial denitrification, and phosphorus reduction. Tertiary treatment processes included ferric chloride chemical coagulation/clarification followed by granular media filters, pre-ozone and granular activated carbon (biologically enhanced activated carbon), and ozone disinfection. The selected process train for the Phase 2 plant expansion treating secondary effluent included: 1. Metal salt coagulant addition/clarification for reduction of phosphorus, organics and solids 2. Screening with drum-type in-channel prefilters 3. Particle filtration with ultrafiltration for turbidity and particle (pathogen) removal 4. Blending with the existing media filter effluent followed by pre-ozone/granular activated carbon for organics removal 5. Final ozonation for disinfection. In the summer of 2002 a three month Membrane System “Proof Test” was started with the ZW- 500c pilot-scale system to confirm design criteria and projected operating costs. Simultaneously, preliminary design commenced incorporating the membrane system into the construction contract documents for the full-scale facility. The UF system consists of 16 parallel process trains with a high degree of redundancy for added reliability. Full production capacity 48 mgd permeate can be met with 14 trains in service and all critical auxiliary equipment and piping are designed for redundancy with backups. Each train has a capacity of 3.6 mgd feed flow and operates at a minimum recovery of 96% at 20 C. The Phase 2 construction began on the AWT (advanced water treatment) facilities in the second quarter of 2003. The testing and commissioning of the first four trains’ 12.5 mgd total capacity began in late 2005. By June 2006, all sixteen trains were operational. This paper will summarize the process design of the membrane facility, start-up activities, and operational data during the first full year of operation. The 50 mgd ultrafiltration system is one of the largest membrane facilities in the world and the largest membrane plant in the Eastern USA.