SEAFOOD GUMBO IN A COMPOST VESSEL

County of Pasquotank, North Carolina builds rotary drum to compost seafood/crab processing residues, wood chips, fresh produce discards and shredded paper.

WITHIN the next month, an in-vessel system is scheduled to begin composting seafood and crab processing residues - along with other feedstocks - at the Pasquotank County Landfill in Elizabeth City, North Carolina. "We want to remove some of the wet waste from the waste stream," says Michael Etheridge, the county's solid waste director, "and with the rising cost of landfilling, we want to experiment with other options." The county received $30,000 from the state's Division of Pollution Prevention and Environmental Assistance (DPPEA) to fund the project. The DPPEA is part of the North Carolina Department of Environment and Natural Resources.

According to Etheridge, the in-vessel system - derived from several different units and built by a local fabricating shop - has limited capacity, but will allow for testing feedstock recipes, aeration rates, etc. Following are estimated tons to be processed in a 12-month period: Wood chips - 52 tons; Seafood residues - 13 tons; Food residuals - 8 tons; Shredded paper - 4 tons. "With an average processing time of four weeks (including curing), this test system should produce approximately 78 tons in a 12month period," Etheridge figures. "This is only an estimate; we hope to reduce processing time of the compost. After the trial period, volumes of feedstocks will increase significantly."

MIXING PAD, CONVEYORS AND THE DRUM

The bulking agent is stored on the landfill site outside the compost area. An agreement has been established with local producers for hauling the needed material. A concrete pad with a side and backboard has been built. A six-inch layer of wood chips will be placed on the pad and the other material (seafood, produce, or food residuals) will be placed on top. The amount of chips needed to complete the mix will be placed on top of the material. The operator will combine the material with a front-end loader using the tumbling method, then load it onto a conveyor, which feeds the rotating drum where it will be more consistently mixed.

After sufficient time in the drum, material will be placed in the curing area. The system has four four-inch portholes in each end of the drum with screens and an airtight cap to control air going into the system. The compost system is plumed for forced air. There are two two-inch smooth wall pipes running the length of the drum and secured in place; one-quarter-inch holes are drilled two feet from the end at two-feet intervals for the entire length of the drum.

On the exit of the drum, the pipe connects to the blower system with a swivel coupling. A half horsepower blower is connected to the two-inch pipe to power the forced air system. The speed of the drum will be determined at set-up. If the temperature becomes too high, the turning rate will be increased; if the temperature is too low, it will be decreased. The feed end of the system rests on two heavy duty hydraulic trailer jacks to allow the unit to be raised to help empty the drum. The drum has six pieces of angle iron mounted the full length of the unit to move material inside the container. The feed end of the drum has a 24-inch opening, and the exit end has four 12-by-12-inch slots to remove materials. The four slots have airtight removal doors.

The unit has two permanent probes, 48 inches in length, installed as monitoring devices - one located one-third of the way down the drum and the other two-thirds of the way down. Steel pipe casings are used to protect the probes. A digital compost thermometer will be attached to the probe at the time of each reading for temperature information. There are holes with airtight plugs located one-quarter, one-half and threequarters of the length of the drum for a thermometer and moisture meter, which will be used as a back up.

Residence time in the drum will be a minimum of five days (to be determined during start-up). PFRP (pathogen reduction) will be met while the material is in the drum. The temperature of the compost in the drum will be kept at least 130F for three days. Vector attraction reduction requirements will be met in the windrows after removal from the drum. Temperatures will be monitored every working day in the drum and every working day in the windrows for at least two weeks. The windrow will be turned as necessary to maintain adequate aeration.