COMPOSTING: Program Uses In-Vessel Composting To Prevent Odors

Del Freeman

Controlling the odors generated in composting facilities is a problem that has plagued the waste industry for years. A new tunnel system, that has been tested by a joint venture, is working toward lessening the smelly stigma of compost.

The composting team, which included Wehran EMCON engineers, a Rutgers University professor and assistance from private hauler Con-solidated Waste Ser-vice, used their individual specialties to contribute to the 14-month pilot project.

The container-type system uses re-circulated processed air to manage the composting microbial ecosystem. It is unique because ma-terials are composted in a very small volume and are virtually odor-free outside of the composting environment.

Wehran EMCON, the engineering consulting firm that re-cently completed the pilot program for O-cean County Landfill Corp., re-ported positive results from the pi-lot, according to Senior Engineer Wes Gavett.

The in-vessel composting project employed a tunnel that was 40 feet long by eight feet wide and eight feet high for testing purposes. The tunnel would be much larger for full-scale use, Gavett said.

The test program included 10 pi-lot runs through the tunnel for en-gineers to determine which technology would be the best one for solid waste and to evaluate organic source separation.

"We looked at fractions of the waste stream and then at chemical compounds or the levels of various types of chemicals and the quality of compost created by different types," said Gavett (see table). "Some of the batch runs had sew-age sludge as well."

The completely enclosed process loads the waste into the tunnel on a fabric-covered grate to a depth of approximately five or six feet. The air then circulates through the tunnel and is forced up through the grate and through the waste, Gavett said.

The method conserves air handling since the same air can be recirculated repeatedly through the waste, according to Gavett. Sensors along the tunnel monitor the temperature, oxygen content and various process levels of composting and the fresh air is introduced as needed.

"From a composting perspective, you want to make sure the process is aerobic, or happening with oxygen," Gavett said. "From an air handling viewpoint, tunnels are better in maintaining aerobic activity." When dispelled, the air used for composting does not retain odor because the constituents of the exhaust are primarily water-based, as opposed to odor retainers such as methane or methane by-products, Gavett said. Composting un-der these conditions renders the used air concentrated so it is easier to treat prior to release.

Although working with an organic waste stream, Gavett said that the costs of the pilot program were no greater than source separation efforts. Preliminary studies indicate the disposal fee for organic waste at a full-scale facility will be ap-proximately $45 per ton.

Private haulers and municipalities collected the material for the pilot program, but in a full-scale operation the public will be encouraged to source separate. Incentives such as lower hauling rates will be offered to restaurants that source separate organics.

"The results with this technology were very effective in accelerating the composting process and controlling odor," Gavett said. "In fact, it was so successful that a full-scale project has been permitted and is now under construction." Mixed waste will not be accepted in the full-scale project.

During the pilot program, the end-product was used as landfill cover, but Gavett said that there are oth-er ready markets. "We feel the end use will be for agricultural and horticultural applications such as top dressings on golf courses in lieu of fertilizer. Landscapers and nursery owners will find a ready use for it as well," Gavett added. Funding for the pilot program was jointly provided by the Ocean County Landfill Corp. and Wehran EMCON.