Laundering Leachate

Cheryl Dunson

Nestled in the foothills of Georgia's Blue Ridge Mountains, Habersham County is a picturesque community that plays host on the weekends to whitewater thrill seekers and fly fishermen.

With a population of 30,000 and an average waste generation rate of 80 tons per day, Habersham County surprised many of its peers with its leap into a Subtitle D landfill in 1993. While local officials met the permitting process and construction of the facility with relative ease, leachate generation rates and potency soon began to plague the 33-acre landfill once it became operational.

"After hauling leachate to the local wastewater treatment plant for six months, our leachate parameters exceeded the plant's standards," recalled Stanley Duckett, the landfill supervisor. "When we were forced to haul leachate one hundred miles one way to a private treatment facility, we knew we had to do something."

Duckett sought relief in a reverse osmosis treatment system manufactured by Rochem Separation Systems, Torrence, Calif. (see photograph on page 76). "Rochem agreed to perform a pilot program and clean 100,000 gallons of leachate," he said. "But, we had difficulty getting the state regulators to work with us because they'd never heard of the system."

Although Duckett and his staff were returning the leachate to drinking water standards, regulators with the Environmental Protection Division of the Georgia Department of Natural Resources continued to insist that the refined liquid be disposed of at a wastewater treatment facility.

"We were doing lab work every day to compile a history of the system to gain state approval to do something different with our leachate," Duckett said. "We eventually petitioned the state to use the purified leachate for irrigation and dust control inside the monitored areas of the landfill. Within 10 to 12 months, the state finally gave us its blessing."

The technology employs a series of sand and cartridge filters to cleanse the leachate before routing it to four modules consisting of 165 membranes powered with 900 pounds of pressure. To adjust pH levels, the leachate is processed through a lime filter and then a carbon filter which "polishes" the water.

Once the leachate reaches drinking water standards, it is diverted to a 90,000-gallon synthetically lined pond. The entire system sits in a 12-foot by 16-foot building near the landfill's 270,000-gallon leachate storage tank.

System maintenance is a must, but it is easy to achieve since all filters and membranes are computer activated. "We clean the membranes every four or five days with special soaps that protect them," Duckett said. "Cartridge filters are replaced daily, and the entire system will automatically shut down if they become clogged."

Reluctant to share costs since Habersham County began as a pilot program, Duckett said the price of replacing filters and cartridges is insignificant when comparing it to a 200-mile round trip hauling bill.

Pick Your Poison Not only are pretreatment systems available for leachate, but they can be fueled by other potential landfill nuisances like methane gas.

Organic Waste Technologies Inc. (OWT), Fairport, N.Y., developed a leachate evaporation system (LES) that uses landfill gas to heat and vaporize leachate. "LES and its sister technology, Technair, remove water by humidifying gas brought into direct contact with leachate," said Barry Rogers, OWT's manager of energy recovery. "LES employs hot combustion gas for heat and mass transfer, while Technair evaporators use air that has been heated by a landfill gas burner."

When leachate transportation and disposal costs began to impact the Orchard Hills Landfill in Watervliet, Mich., in 1992, company officials began weighing their options. Since the landfill's methane gas was treated within an enclosed flare, LES was a good alternative.

"The primary criteria is financial," Rogers said. "Certain landfills produce a lot of leachate, but their disposal costs may be low. In that case, when you're talking capital costs of more than $499,000, it may not be financially worth it to invest in a system."

However, considering Orchard Hill's leachate disposal costs of 11 cents per gallon plus a 40-mile transportation expense, an evaporation system made sense. Today, the landfill evaporates an average of 6,000 gallons per day of untreated leachate which requires one hour of labor.

"Tax credits play a very important role," Rogers emphasized, referring to the program established by the U.S. Environmental Protection Agency, Washington, D.C. "We set ourselves up as a [gas] treatment company or a leachate company. We own and operate the equipment, and provide the landfill with leachate evaporation services. The landfill is the gas company. We buy the gas to fuel the equipment, and the landfill qualifies for tax credits which are worth as much as a four-cent-per-gallon reduction in leachate treatment costs."

Osmotek Inc., Corvallis, Ore., offers landfill managers a direct osmosis concentration system to treat leachate which results in the removal of at least 95 percent of water. Robert Salter, president of Osmotek, said the process was originally rooted in the food processing industry as a liquid separation technology. When a landfill operator approached him about the feasibility of treating leachate with the same process, a series of studies indicated it was a good opportunity.

"Our technology is driven by osmotic pressure differential," Salter said. "It uses a microporous membrane that separates a feed stream, or leachate, from a brine solution."

The brine solution prevents membranes from becoming "fouled" and is capable of reducing leachate volumes by 20 times or more. Although the technology hasn't been implemented in a full-size landfill, pilot programs are ongoing in the Corvallis community, and Rogers is confident increasingly stringent wastewater disposal regulations will eventually mandate some form of pre-treatment at most landfills.

Integrated Leachate Management What began as a single-faceted leachate management approach for Steve Wolfe at the Kootenai County Landfill, 13.3 miles south of Couer d'Alene, Idaho, evolved into a multi-faceted integrated discipline. The solid waste director oversees activities at the state's first fully-lined landfill.

The ornery Pacific Northwest weather, coupled with Wolfe's willingness to experiment has resulted in an ecological collection of native trees, grasses and cattail ponds sustained by the landfill's leachate.

Working with Dwight Miller, waste containment division manager for Parametrix Inc., Kirkland, Wash., Wolfe developed a fully-integrated leachate management system that emphasizes internal and external leachate reduction.

"We initially spent money for a permanent system that allowed us to pull high-strength leachate from ponds and return it to the landfill," Wolfe said. "We've gone through extreme weather in the Northwest for the last three years, and we soon realized a single-faceted approach wasn't going to solve our leachate problems."

Because the leachate lagoon aerators were undersized, leachate turned septic and began causing odor problems. Attempts to combat the problem with nitrogen and the addition of activated sludge from the community's wastewater treatment facility failed.

"Once we started looking at the numbers, we realized our CODs were extremely high, and the bugs couldn't compete," Wolfe said. "Everything was out of whack. So we came in with 50 percent hydrogen peroxide, and the leachate went from extremely black to a tannish color."

Wolfe and his staff enhanced their re-injection process with lined outside slopes to minimize leachate production and increased lagoon aerators from five to seven horsepower.

An elaborate irrigation system came next which provided more flexibility in the landfill's recirculation system and added a new dimension to the landfill's appearance. "We installed four to five feet of clay material [as intermediate cover] across a half acre of landfill, sealed off the gas and designated an area for Poplar trees which have a high affinity for water," Wolfe explained. "When we return to that area of the landfill in three or four years, we'll remove them."

Initially, Wolfe said he was skeptical whether the trees would thrive on leachate. "We had such high BODs and CODs that I thought, 'Geez, nothing can grow in this stuff.' But, they've done well."

Wolfe's attempts at growing canary grass haven't been as successful due to the leachate's high organic blend. "The grass seed molded and rotted before it had a chance to sprout," he said. "It'll take more nurturing to get it to grow, not like the trees that are pretty withstanding."

As the landfill developed, so did the need for additional leachate overflow capacity. A quarter-acre claylined pond was constructed, and cattails seeds and plants were added.

Although the solid waste industry views these practices as cutting-edge, most pre-treatment leachate methods are old hat to other industries, according to Miller.

"We're just like a factory, trying to reduce wastewater," he said. "If you're not looking at all your options, you're paying more than you should. You're failing your facility and the rate payers, who want the most competitive rates."