Innovative membrane technology used at Georgia wastewater reclamation facility

Scheduled for completion later this year, the new $27 million Forsyth County, Ga., system designed by Metcalf & Eddy includes a 180-acre drip irrigation system, and a 2.5 million-gallon-per-day advanced wastewater reclamation plant. The plant, which uses membrane bioreactors to produce a high quality, reusable effluent, with very low nitrates and phosphorus, will be one of the largest of its kind in the nation...

WAKEFIELD, MA, Dec. 28, 2004 -- Water needs are a point of contention for the Atlanta metropolitan area and similar southern cities with rapidly growing rural areas. This was a major consideration when Forsyth County, Ga., one of the nation's five fastest growing communities, decided to establish a new wastewater infrastructure system. The county hired Metcalf & Eddy to design, build, and operate a facility that would provide high-quality wastewater treatment, and would also reclaim the treated wastewater (and minimize the use of valuable fresh water supplies) for non-potable uses, such as landscape irrigation.

Scheduled for completion later this year, the new $27 million system includes a 180-acre drip irrigation system, and a 2.5 million-gallon-per-day advanced water reclamation plant. The water reclamation plant will be one of the largest of its kind in the nation. The plant uses membrane bioreactors to produce a high quality, reusable effluent, with very low nitrates and phosphorus.

"The key issue for the County is treatment reliability," said Nick Cooper, the M&E Senior Project Manager. "The regulatory requirements for urban water reuse are understandably very stringent. After all, one of the planned uses is lawn watering for residences where children may have contact with the water." Many safety features have been incorporated into the design to ensure consistent quality of the treated water.

The County plans to provide reclaimed water for golf course and irrigation customers in subdivisions in the southern part of the County. At some point in the future, the effluent may be injected into the nearby Chattahoochee River.

Membrane Technology Produces High Purity Effluent
Membrane treatment is an emerging, leading-edge technology that, while twice as expensive to implement as a more traditional wastewater reclamation plant, produces a consistently high-quality effluent.

At the Forsyth County plant, once the wastewater has gone through the screening and grit removal process, it will enter the membrane bioreactor tanks. The membrane filters are immersed in the wastewater. The effluent is extracted through the membranes, and all of the solids are left behind in the treatment tank. "The membrane filters produce a high purity discharge because the filters have very fine pores, finer than the pores in your skin," said Cooper.

The clear membrane effluent is disinfected using ultraviolet disinfection for virus control. The treated water then travels through an 11-mile pipeline to the 180-acre, underground drip field. Since membrane treatment requires smaller tanks and fewer treatment unit processes, M&E was able to compress the plant footprint to a single building of an acre in size ¿ a quarter of the size of an activated sludge plant. "Because the system is in a building, odors can be captured and treated easily," said Cooper. "Since the facility is being constructed on the same property as a new County park, these are key advantages."

Largest Drip Field in the Southeast U.S.
Another key feature of this project is the 180-acre, underground drip irrigation system. Based on technology developed in Israel, this system will be the largest in the southeast US, with nearly two million feet of drip tubing. It will use an automated control system, which will be monitored at the reclamation plant, to open and close the hydraulically operated irrigation valves in each field to accommodate ground conditions. To tailor the system to the varying soil conditions, M&E conducted soil percolation tests in each of the 22 irrigation fields.

"The advantage of this system is that subsurface irrigation can occur year round because the pipes will be located about a foot below ground and will not be affected by weather," said Cooper.

Fast-track Implementation
The permitting process was a complicated one. Although this is a design/build project, it had to go through the normal permitting process at the state regulatory agency for municipal treatment facilities. The construction was done in phases, with portions of the design occurring at the same time. The construction of the facility is progressing on schedule to meet the planned Fall 2003 completion date. Once the plant is online, M&E will operate and maintain it for 20 years. "For rapidly growing communities like Forsyth County that face very stringent water use restrictions, water reuse facilities using membrane technology can provide a valuable water resource," said Cooper.

About Metcalf & Eddy
Founded in 1907 and based in Wakefield, Mass., Metcalf & Eddy ( employs over 1,000 professionals on environmental and infrastructure projects all over the world, from wastewater treatment in Boston to desalination in the Gaza Strip.

In 2001, M&E became the environmental flagship of the AECOM Technology Corp. ( group of professional services companies, which together employ more than 17,000 people and generate annual revenue in excess of $1.7 billion. We are thrilled to be part of this highly successful group and to offer our clients the many benefits of our access to AECOM's financial resources and our sister companies' broad project experience.


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