Prepared by

North Carolina Cooperative Extension Service

Rhonda Sherman, Waste Management Extension Specialist

Biological & Agricultural Engineering

Box 7625, Raleigh, NC 27695-7625

Phone: (919) 515-6770 Fax: (919) 515-6772

e-mail: sherman@eos.ncsu.edu

Web site: http://www.bae.ncsu.edu/people/faculty/sherman

Composting at Caledonia Correctional Institution

Caledonia Correctional Institution is located on 7,600 acres in Halifax County, North Carolina, not far from the Virginia border. Some 5,000 acres are used to raise crops which are sent to inmate kitchens throughout North Carolina, and an on-site cannery processes vegetables grown at prisons all over the state. Caledonia also raises 2,000 cattle and thousands of layer and brooder chickens. There are 700+ inmates at this maximum-security facility, 500+ honor grade inmates at Tillery Correctional Center next door, and 500+ maximum-security inmates at Odom Correctional Institution nearby.

In its commitment to reducing waste, Caledonia recycles old corrugated cardboard (OCC), PETE and HDPE plastics, glass, and aluminum cans. Although office paper is not presently being recycled, they are considering shredding it for composting or recycling. Instead of sending Caledonia's kitchen scraps to the landfill, they were collected two or three times a week by a nearby hog farmer. When hog prices plummeted in 1997, the hog farmer cut back on food scrap collection, and prison managers scrambled to find another method of keeping the materials out of the landfill. They obtained a one-year pilot permit from the state which allowed them to implement windrow composting. In the meantime, they applied for a permanent facility composting permit and began designing and constructing bins for in-vessel composting. As soon as the permit was approved in May 1998, they began composting in aerated bins.

The $40,000 forced-air static composting system was designed by the prison's maintenance supervisor and carpenter. The system consists of 12 bins, divided into two rows of six, and each bin is 7 feet long by 7 feet wide by 5 feet tall. The front of each bin has six 2 by 8's that can be removed two at a time by a person on each end. The capacity of each bin is 36, 35-gallon barrels, or 96,000 pounds of food scraps. The floor of each bin has 16 BioPlates for aeration and leachate. The BioPlates, constructed of fiberglass and concrete at a cost of $89 apiece, are strong enough to withstand the weight of a Bobcat. A 980 cubic feet-per-minute fan for each bin is operated on a timer to aerate the pile by forcing air through the center of the system and up through the BioPlates in the floor. When aeration is needed, usually for moisture reduction, the blowers run for 10 minutes every hour on the hour. Moisture is usually added at a rate of 25 gallons at a time by placing a portable irrigation sprayer on top of the compost pile that uses a 3 gallon-per-minute electronic water meter. They presently use the "dig and squeeze" method of moisture testing, but plan to obtain an electronic moisture reader. An overhead irrigation system was considered but rejected due to the prohibitive cost of purchasing an electric water meter for each bin ($113 for each meter) to meet the requirement of keeping daily records for their permit. Leachate runs to a trough between the two rows of bins and into a 1,500-gallon septic tank. The collected leachate is handled by three alternative methods--either added to bins to increase moisture levels, or land-applied as allowed by their permit, or processed at their wastewater treatment plant.

Caledonia is composting food scraps, paper products from the kitchen, 100% cotton t-shirts, and bones. About 12 barrels (35-gallons each) a day are generated of food preparation waste, leftovers, and scrapings from inmates' plates. When all of the bins are operating, they plan to compost cannery waste plus kitchen scraps from two smaller correctional facilities next door. Because the maximum security inmates housed at Caledonia are ineligible to work at the composting facility, a team of three inmates from the minimum-security facility next door use a Bobcat to fill and empty the bins. Wood chips, obtained at no cost from a nearby paper company, are used as a bulking agent. Inmates apply a 4-inch layer of wood chips (two Bobcat scoops or 420 pounds) on the bottom of the bin, then add 4- to 8-inches of food scraps (12 drums; 195 pounds), then 10 pounds (5 scoops) of 46 percent nitrogen urea from a fertilizer company (to increase pile temperature). This procedure is repeated three times until the bin is almost full and then capped with a 4-inch layer of wood chips. From May through December of 1998, Caledonia composted 41,135 pounds of organic materials.

Organic materials are composted for about two weeks, and then the bins are emptied into windrows for at least two months of curing. So far, Caledonia has been using most of the compost as a bulking agent in the bins because the wood chips and compost can be reused three times for this use. Eventually the compost will be screened and used to grow day lilies or spread on fields for crops.

Caledonia has experienced some problems with their composting system. The biggest challenge occurred this past winter when bin temperatures would not rise enough to meet their permit requirements. This problem was attributed to the BioPlates laying on a concrete pad that did not allow the bins to hold heat. They tried wheat straw and poultry litter separately as bulking agents, but both compacted so much that the forced-air system didn't work and inmates had to hand-turn the piles. They also need to lay asphalt around the bins because the gravel doesn't come up to the sides of the bins and it hangs up the Bobcat. Furthermore, the bin system needs more overhang and curtains on the sides to keep out rain.