Old Leachate Performs New Tricks

While many municipalities are spending time and money to collect and remove wastewater from their landfills, Chattanooga, Tenn., is doing just the opposite. In an attempt to speed decomposition, reclaim airspace and reduce environmental hazards, Chattanooga will conduct a study to determine the effects of pumping leachate back into its landfill.

Through a process called aerobic bioreclamation, the city will add air, wastewater and other nutrients to 200,000 cubic yards of municipal solid waste (MSW) in a 4-acre corner of the landfill. To determine whether economic benefits justify the project's $450,000 price tag, the city will measure recaptured airspace, reductions in leachate treatment and methane management costs, and the quality of the compost created.

Last October, the city received the required modification permit for the test site and hired ARCADIS Geraghty & Miller Inc., Chattanooga, Tenn., to design the system.

In February 2000, city solid waste staff completed filling the test site with MSW and applied a 1-foot-deep cover. Immediately thereafter, ARCADIS installed injection wells, monitoring devices and piping, which are designed to re-circulate leachate continuously through the site while injecting air and nutrients.

To balance the system, AR- CADIS will install temperature and off-gas monitoring equipment, and will measure the stability of the waste material weekly. As the material begins to stabilize, the engineers will conduct more direct quantitative sampling to determine the makeup of the finished product.

At that point, city solid waste staff may place additional waste in the site, thereby reclaiming airspace and extending the productive life of the landfill. Project manager Damon Riggs predicts that this process, if applied throughout the landfill, will extend the landfill's life by at least 30 percent and reduce future monitoring costs.

"Because the waste is decomposed more rapidly to an inert form," Riggs says, "the need for long-term monitoring after closure may be significantly reduced."

Jack Marcellis, administrator of Chattanooga's Department of Public Works, also has high hopes for the project. "I hope the project will provide us with more landfill space, and we will be able to market the compost material for another use," he says.

According to Riggs, the compost could be sold or used at the landfill as alternative daily cover.

Another benefit to aerobic bio-reclamation is that it reduces methane production, says William Johnson, developer of the system.

"There is no methane gas byproduct, and the offensive odors associated with landfills [are] reduced or eliminated," he explains. "In addition, the higher temperatures created by the process destroy many disease-causing organisms."

Johnson expects to see compelling results from this project by the end of the year.

"For this pilot study, we expect to be in operation from nine months to one year," Johnson continues. "Final testing of the waste mass and reporting of the outcome will bring the pilot study to a close."

Results from similar studies are fueling Johnson's optimism. When aerobic bioreclamation was tested on a Georgia landfill, a high-quality compost material was produced within the first five months, Johnson says.

Additionally, methane production virtually ceased at the Georgia site, and minimal leachate was collected during that period.

If ARCADIS' study proves that the aerobic bioreclamation system is economically viable, the city plans to implement similar systems throughout the landfill.