WATER RECLAMATION PLANT ON HIGH GROUND
Abstract:Gwinnett County is in the Piedmont region of Georgia where streams have finite assimilative capacity. Gwinnett County is also upstream of water supply and recreational waters for much of the Atlanta metropolitan region. This headwaters geography has required the county to adopt advanced water reclamation methods to keep pace with increased demand for wastewater service.
In January, 2001, Gwinnett County started operating the 20 mgd F. Wayne Hill Water Resources Center (WRC). This plant is designed on a multiple barrier concept for both conventional pollutants and nutrients. Monthly average effluent limits are as follows:
Treatment processes include: 1) preliminary treatment with fine screening and vortex grit separation, 2) primary clarification, 3) activated sludge with anaerobic, anoxic and aerobic zones to maximize nutrient uptake, control filaments, and denitrify, 4) secondary clarification, 5) highpH lime clarification, 6) recarbonation to neutralize the pH, 7) granular media filtration, 8) ozonation, 9) granular activated carbon adsorption, and 10) ozone disinfection. Biosolids are centrifuge-thickened, anaerobically stabilized in egg-shaped digesters, and dewatered by centrifuge prior to landfill disposal. The 20 mgd plant includes a permanent membrane demonstration facility with a 1 mgd forward-flow capability. A 40 mgd expansion (currently under design) may use membranes in conjunction with the physical-chemical advanced treatment processes.
The Hill WRC is near the subcontinental divide, which splits drainage into the Atlantic Ocean and the Gulf of Mexico. All sewage treated at this plant is pumped up to it from remote locations, and the reclaimed water is pumped through a twenty-mile effluent pipeline to its outfall location. This pipeline will become the transmission main in a growing nonpotable distribution system.
Gwinnett County has made an investment in reliability at the Hill WRC that far exceeds EPA Class I reliability criteria. Examples of reliability include three power feeds from two separate substations with independent transmission mains, plus on-site generation capacity if both substations are disabled. “Multiple barriers” refers to a series of treatment steps, each of which may be sufficient to remove a pollutant to a level which meets discharge limits; these multiple barriers are nonetheless sequenced for reliability. Additionally, the plant has a significant amount of installed redundancy. Each treatment step is designed to handle peak flows within its design criteria even when one unit is out of service, whether that unit is tankage, piping, or equipment. Filters and absorbers are designed to handle peak flow even with one in backwash and another down for maintenance. Further, the plant has 40 million gallons of tank storage to either equalize influent flows and/or store off-spec water for re-treatment. Another 20 million gallons of tank storage will be used to dampen diurnal fluctuations and provide steady flows to the advanced treatment train. The instrumentation and control system data highway is redundantly looped around the plant, and the control system itself is a distributed control system. On-line instrumentation will provide real-time feedback on surrogate and sentinel parameters such as TOC and turbidity.
The combined cost of land, design, and construction for the 20 mgd plant was around 245,500,000, with the effluent pipeline adding 30,500,000. The plant is on a 700 acre greenspace, and is designed to be a good neighbor with ample visual buffer and odor control. The reclaimed water is suitable for return to water supply, for recreation, and for any nonpotable uses. The Hill WRC is considered a model for other plants in northern Georgia with its advanced technology and reliability. The plant was named in honor of Gwinnett County's threeterm chairman who championed the facility and its advanced technology.
Document Type: Research Article
Publication date: 2001-01-01
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