Preston ― David Aldridge brought something to show the Planning and Zoning Commission last Thursday ― a bag of dirt.

The bag contained compost created from a pilot food waste composting operation at the Stonington transfer station.

Aldridge, the executive director of the Southeastern Connecticut Regional Resources Recovery Authority, brought the material to show the PZC the success of the pilot to create the type of commercial grade material that would be produced at a proposed food waste composting facility on the grounds of the Preston incinerator.

After an hourlong public hearing on how the process would work and safeguards to prevent odor and water leakage, the PZC voted unanimously to approve the composting plant.

Aldridge said preliminary estimates put the cost of the facility at about $2 million. The authority still needs state Department of Energy and Environmental Protection permits, which could take a while, Aldridge said, because this could be the first aerobic food waste composting operation in the state.

Aldridge said project officials will meet with DEEP to discuss the project and will apply for state and federal grants to help fund the operation.

“We very much would like to be a prototype for the state,” Aldridge said. “If you can align funding, this is an easy way to line up six of these across the state. We very much want our process to be easily duplicated. This is local. You take what you generate locally and dispose of it locally.”

The property at 132 Route 12 is owned by the 12-town regional trash authority, which leases 11 acres to Covanta, which owns and operates the trash incinerator. The composting operation would be run by SCRRRA independent of the incinerator.

SCRRRA already owns critical equipment needed for the operation, a giant wood and stump grinder.

The composting formula requires four parts wood chips to one part food waste, project engineer Greg McCarron, of SCS Engineers explained. Previously, SCRRRA had to pay to dispose of the wood chips, which are not commercially viable, Aldridge said.

Trucks would drive into the plant and dump food waste onto a prepared bed of wood chips and mulch, which absorb the liquid. More wood chips would be mixed into the food waste, absorbing the odor and gas generated by the rotting food.

The material would be placed in the initial composting bin for two weeks. Probes would measure oxygen and moisture levels to determine how much air and water should be added. Rainwater and any liquid emitted from the waste would be collected and used for the composting operation, McCarron said.

After two weeks, the pile would be moved to the second bin for two weeks, then remixed and placed in a windrow, a long straight row of material.

“The food itself disappears in the first two weeks,” McCarron told the PZC. “It’s a continuous process. It does take time, and you age it. Before you put it out for sale, it’s really broken down and homogenized.”

Aldridge said on the first day of operation of the much smaller Stonington test site, officials placed a 10-pound roaster chicken into the pile.

“Ten days later, it was gone,” Aldridge said.

The Stonington pilot has ended, and SCRRRA worked to find a site for the larger, permanent operation. The Preston site would take in food waste from the 12 authority towns and beyond. Food drop-off sites could be placed in the region, collected in biodegradable bags made of corn.

McCarron said the compost would be tested regularly to ensure quality. No chemicals would be used in the process and no manure or outside plant materials would be added.

SCRRRA plans to sell the compost in bulk to landscape companies. No residents would be allowed on site. Eventually, SCRRRA could add a a bagging operation to expand sales, Aldridge said.

c.bessette@theday.com