Redistributing wastewater

Forsyth County, Ga., has built its first wastewater treatment plant, which features technology that recycles wastewater so it can be used to irrigate agricultural areas, golf courses or parks, and can be discharged safely to the environment. The Fowler Water Reclamation Facility (WRF) currently serves only 13 percent of the county’s sewer customers — about 2,350 people; however, usage will increase as the population continues to grow and pumping stations are installed to deliver more wastewater to the plant.

Until the Fowler WRF began operating in January 2004, only the county seat, Cumming, was serviced by a wastewater treatment plant. The rest of the county used conventional septic systems or sent wastewater to a treatment plant in neighboring Fulton County. However, Fulton County could accommodate only up to 2 million gallons a day (mgd) of wastewater from Forsyth County, and, as the population grew and flow volume approached the limit, the county needed an alternative treatment option.

In addition to increasing wastewater volume, the county also had to deal with decreasing surface and groundwater levels. Most of Georgia receives 40 to 50 inches of rainfall annually; however, in recent years, a lengthy spell of unusually dry weather combined with steadily increasing water demand has diminished the state’s water wealth. As a result, communities are acting more frugally with resources and are beginning to develop long-term water conservation and reuse strategies.

Forsyth County turned to membrane bioreactor (MBR) technology as one way to cope with the variability of rainfall and the increased pressure that its growing population was placing on water resources. Working with design/build firm Wakefield, Mass.-based Metcalf & Eddy, Forsyth County selected ZeeWeed MBR from Oakville, Ontario, Canada-based Zenon Environmental to use in the Fowler WRF. The MBR system combines biological processes with immersed, hollow-fiber, ultrafiltration membranes in a compact footprint. The hollow-fiber membranes used in the MBR process incorporate a reinforced structure and can withstand the high-solids environment of wastewater. That allows the membrane cassettes to be immersed directly into the final process tank of the MBR system and contributes to the reduced size of the plant by combining clarification and aeration into one step.

Hollow-fiber membranes are thin, flexible strands of porous plastic fibers with billions of microscopic pores that form a physical barrier to suspended solids and colloidal material in the wastewater. A slight suction is applied to the end of each fiber to create a vacuum that draws clean water inside while blocking contaminants on the outside. Bacteria, viruses, and other pathogens also are prevented from passing through the membranes, and effluent can be released into the environment after being treated by the plant’s high-intensity ultraviolet lights. The effluent released from the Fowler WRF typically has a biological oxygen demand of 1.2 mg/L, total suspended solids of 1.0 mg/L, turbidity of 0.23 nephelometric turbidity units, pH ranging from 6.3 to 7.2, and non-detectable fecal coliforms.

Forsyth County’s MBR system is contained in one building that occupies only about one quarter of the space that a conventional plant with the same capacity would have required. An 11.5-mile network of 20-inch pipes also has been constructed to deliver the recycled water to golf courses, parks and farmland throughout the county. The $27.6 million project includes a 284-acre land application site that uses subsurface drip tubes to irrigate a field leased for hay production.

Forsyth County plans to build pumping stations to divert the flow of wastewater back to Fowler WRF rather than releasing it to Fulton County. As a result, the Fowler WRF will increase wastewater treatment from the current 0.5 mgd to its design capacity of 2.5 mgd. Over time, the central sewer system will be expanded to include more businesses and residences, and the Fowler WRF may grow to handle 10 mgd.
— John Marshall, Forsyth County, Ga., Water and Wastewater Plant Manager