The reclaimed water reaching the golf courses has undergone treatment at the new, 500,000 gallon-per-day Pumpkinvine Creek Water Reuse Facility. The zero-discharge plant resulted from a mutually beneficial collaboration between public and private interests that now benefits the golf courses, developers of the upscale subdivisions and Paulding County Public Works Department.
The residential communities - planned to have 1,750 home sites in Bentwater and 550 lots in Governor's Towne Club - were staked out across more than 1,700 acres of hilly timberland northwest of Atlanta. Located well beyond the reach of existing collection and treatment facilities, the developers wanted to avoid marketing the expensive home sites served by septic tanks. Public/private agreements therefore were reached to underwrite the construction costs of the collection system and water-reuse facility. The plant sits on a 125-acre site adjacent to the golf course. The County rejected the initial offer of a plant site within the Bentwater development to gain the flexibility for anticipated plant expansion.
Developers of Bentwater invested upwards of $5 million toward the construction of the original infrastructure in exchange for County collaboration with operations. The developer of the even more upscale Governor's Towne Club community has subsequently pledged more than $3 million to double the treatment and storage capacity. Developers of the subdivisions have paid for the infrastructure construction, including upsizing for future use, and the county is reimbursing them for the oversized facilities through reduced connection fees as their projects build out.
Paulding County Public Works thus gained a state-of-the-art facility whose zero-discharge operation complies with the water reuse standards enacted by the Georgia Environmental Protection Division. The water reuse plant could serve as a model for others needed in the future to accommodate the population growth around the Atlanta area and requirements of the state's water policy.
Infrastructure PowerThe 25-mile long collection system linked to the new plant currently has eight lift stations, with 16 ITT Flygt submersible pumps ranging from 7.5-HP up to 100-HP. The 12-inch force main from the Bentwater 1,050-gpm duplex lift station with two 47-HP pumps, and a 10-inch force main from the Governor's Towne Club duplex 1,215-gpm station with two 100-HP pumps, converge at a surge basin at the headworks.
The process chain for the stand-alone facility uses a Sequential Batch Reactor (SBR) process with four, 125,000-gallon SBR units, tertiary sand filtration and a 120-lamp UV disinfection system. The treated effluent flows through 12-inch lines to one of three reservoirs - a 3-million-gallon holding pond on the Bentwater course, a 14-million-gallon lagoon within the Governor's Towne Club course or a 19-million gallon reservoir constructed at the plant site. Engineers sized the storage ponds to provide more than 45 days of wet weather storage deemed necessary for the Paulding County area that normally receives 60 inches or more of rain per year.
Each SBR tank operates independently with a series of actuating valves continuously feeding the arriving influent to each SBR. The individual SBRs operate on eight-hour treatment cycles. The sewage undergoes a four-hour aeration/anoxic stage, followed by two hours of settling, and then two hours of decant/idle to complete the cycle. The decanted supernatant is directed to tertiary filtration, disinfection and then transferred through 12-inch lines to one of the storage ponds. If the water exceeds 3 NTU (nephelometric turbidity units) after filtration, that batch of water is diverted to a reject pond from where it is gradually pumped back into the SBRs and subjected to another SBR cycle. A duplex effluent lift station with two 130-HP ITT Flygt pumps moves the water restored to irrigation quality standards to the lagoons on each golf course.
Surge Basin RequiredThe plant initially was designed to handle only the flow off the Bentwater development under low-flow design conditions. However, a surge basin was needed at the headworks when a second lift station entered service. The 10-inch force main off the second pumping facility dictated headworks modification to cope with both the additional flow and the pressure of the new line. Without the surge basin, the arrival pressure of the influent in the line off the ridge, more than 70 feet higher than the plant elevation, combined with the Bentwater flow, would create the potential for spills. Engineers designed the surge basin with a holding capacity of 57,400 gallons. The basin has a workable volume of 26,000 gallons, meaning the tank retains 31,400 gallons at all times.
During the first two years the plant was in service, operators had experienced an extremely high food/microorganism ratio when the lift station was pumping - between 6 minutes to 10 minutes per hour at the time - to an extremely low ratio the rest of the time. This start/stop cycle subjected the plant to conditions characteristic of a digester. The construction of the surge basin enabled the plant operators to regulate a constant flow.
Gaskins Surveying & Engineering Co., the Marietta, Ga.-based designers of the lift station network, engineered the surge basin to accept the proposed inflow off the force main. The influent now released from the surge basin remains at a controlled trickle through the headworks and preserves the operational requirements for the SBRs.
The addition of the surge basin to the headworks raised other considerations, however. Not the least of these raised the risk of potential odor off the 3 feet of residual sewage held in the basin and the potential for a sludge blanket to accumulate within the surge basin. Therefore, the surge basin required some method of aeration and base agitation.
Gaskins recommended installing a Flo-Get system in the surge basin. Manufactured by ITT Flygt, this system consists of an integrated submersible pump, an air suction tube and an ejector/diffuser nozzle that deliver a balanced combination of aeration and mixing. The unit now operates for a 15-minute cycle per hour year-round and achieves similar results as compressed air injection or surface aerators, without the addition of compressors or the misting associated with surface aerators.
The Treated EffluentCurrently operating at only 160,000 gallons per day, approximately a third of the design capacity, the plant effluent has lower BOD, TSS and fecal coliform counts than the water found in the plant's namesake creek. The state permit stipulates a monthly BOD average of 5 ppm or less, limits suspended solids to an average of 5 ppm per month, a pH between 6 to 9 and a fecal coliform monthly geometric mean of 23 colonies per 100 ml. The plant effluent consistently stays within the current quality levels, also defined as “human contact criteria.” The treated effluent tests consistently show BOD of less than 2 ppm, total suspended solids are 1 ppm, and fecal coliform counts below detection limits. Plans already are underway to improve the effluent even more, to satisfy state standards for recycling the water for lawn irrigation.
In the current state, the treated water is more than safe enough for irrigation use but has not gone through the same treatment process as drinking water. The reclaimed water contains concentrations of organic and inorganic solubles. Treatment plants with a point source discharge have restrictions on these residuals but not to the quality level of potable water.
The Pumpkinvine Creek Water Reuse facility is one of 24 wastewater treatment plants constructed in the Atlanta area over the past decade that produce recyclable effluent. The two dozen plants are operated by local governments, developers and golf communities like those in Paulding County. An individual 18-hole course often absorbs up to half a million gallons a day during summer months. Pumpkinvine is among the latest of eight plants either proposed or under construction that will have a combined potential output of 55 million gallons per day.