Southeast Drought Sparks Brawls But Reuse Meets One Utility’s Needs
Lake Lanier’s exposed shoreline is worrisome for Atlanta utilities.
“In Clayton County it’s raining every day because we’re putting 10 million gallons per day back into our supply,” says Mike Thomas, general manager of Clayton County Water Authority, Morrow, Ga. “We have 200 days of supply.”
Since 2000, the utility and engineer CH2M Hill Cos., Denver, have pursued a phased plan of transition from land application of treated wastewater to wetlands treatment. The first three phases of wetlands construction have been completed and now treat 10 million gallons per day. Ground has been broken for a fourth phase, expected to add 3 mgd when it is completed in two years, Thomas says.
“It’s primarily a dirt-moving job,” consisting of raising berms to retain water, says Thomas. The cells are planted with seven different species of vegetation both for esthetic reasons and for the protection resulting from natural diversity. “There’s no reason to believe one plant performs better than another,” he says.
The wetlands are being created on land formerly used for land application systems, where treated wastewater was dispersed by pumps and sprinklers and returned to the reservoirs via groundwater migration. They are less land-intensive than the land application systems, requiring only about 10 to 20 acres per million gallons, or 10% of the 150 to 200 acres per million gallons under the land application system, Thomas says. Operation and maintenance costs also are lower. With no more pipes and sprinklers to maintain, the O&M staff of 12 to 15 required for land application has been cut to four people now.
Clayton County utility is converting land to wetlands for water polishing.
Capital cost for the wetlands system also is lower than for other systems. Clayton County’s costs run about $1.50 to $2.00 per gallon of capacity, or $5.00 per gallon including the wastewater treatment plant. A conventional system discharging water treated to a “very advanced” level can cost about $10.00 per gallon, Thomas says. The utility plans eventually to add a fifth phase to the program, boosting wetlands treatment to the permitted level of 24 mgd.
Clayton County’s water use currently averages 26 mgd, says Thomas. The wastewater is treated to advanced secondary levels and pumped directly to the wetlands. Land application still is used for 4 mgd to 5 mgd, and the rest about 10 mgd goes to wetlands treatment. After polishing the effluent to reduce levels of BOD, nitrogen, heavy metals and other contaminants, the wetlands drain directly into the reservoirs. Average retention time is two weeks. “We’ve increased our ability to sustain our reservoirs,” Thomas says.
Water reuse is not a new technology, but “this is larger and unusual in putting water back into the drinking water system,” Thomas says. Some communities have blocked programs to recycle treated wastewater into the drinking water system, denigrating the practice with the distasteful moniker “toilet to tap.” But Clayton County Water Authority has been polishing treated wastewater through land application for 25...��