Solid Waste Utility Manager
City of Columbia, Missouri
What do you do with cellulose casings produced from more than a billion hot dogs a year? The answer for the City of Columbia, Missouri and Kraft Foods is: COMPOST.
The City of Columbia has operated a compost facility since state regulations prohibited the placement of yard waste in landfills in 1991. Columbia is in central Missouri, on Interstate 70 halfway between Kansas City and St. Louis, with a population closing in on 80,000.
Columbia's Public Works Department provides a full range of solid waste management services. It collects yard waste, recyclables, bulky waste, household hazardous waste, and residential garbage from 32,000 households. In addition, it competes with private haulers to collect refuse from the commercial sector, which generates 74 percent of the solid waste collected by the department. The department also owns and operates a 530-acre landfill and 11-acre compost facility located 10 miles from the center of town.
Columbians generate 55,000 cubic yards of yard waste annually. In response to the state yard waste ban, Columbia constructed an 11-acre compost facility which includes an approximate one-acre asphaltic concrete working pad for staging and grinding of materials, a composting and windrowing area, and two holding basins (primary and secondary) for storm water management. The site is regulated by a NPDES (National Pollutant Discharge Elimination System) permit monitored by the Missouri Department of Natural Resources.
The equipment mix includes a Peterson 5400C horizontal grinder, a Morbark 1100 tub grinder, Scat windrow turner, and two 721 Case wheel loaders with grapple buckets and a grapple loader truck combination.
The City collects residential grass, leaves, and small brush weekly from the curb with standard rear-loading packer trucks. Lawn care and tree companies are charged $16.25 per ton for material brought to the compost facility that requires grinding or further processing. All material that enters the site is tracked and weighed at the landfill scales. The site also accepts other wood waste such as pallets and clean lumber for the same per ton fee. In addition, the City operates two residential drop-off sites close to the center of town. These two sites accept residential yard waste only. The yard waste at these sites is ground and given back to residents as mulch or transported to the compost facility for further processing.
While yard waste and wood products have been the mainstream of feed stock for the operation, Columbia has continued to seek out opportunities to increase the amount of material that could be diverted from the landfill through composting. Two very interesting ingredients that have recently been added to the compost recipe are clean drywall and cellulose wiener casings (hot dog processing wrappers).
Drywall was selected for composting because of its ease of segregation. The City began accepting drywall March 1, 1999, and has received over 1069 tons that otherwise would have been landfilled. Contractors have a financial incentive to bring clean drywall to the compost facility because composting fees are half the normal landfill fee.
Operational problems have been minimal. Drywall is dusty to grind, but mixed with yard waste, it is manageable.
Cellulose wiener casings are by far the most interesting composting project Columbia has tackled. Missouri Department of Natural Resources approved this pilot project that began November 22, 1999. To date just over 1,165 tons of wiener casings have been composted or are in various stages of decomposition.
The casings come from the local Kraft Foods-Columbia Food Facility that produces more than a billion hot dogs a year. As a by-product, Kraft generates 32 tons of casings per week. Without the composting project, this material would be deposited in the landfill.
Composting 32 tons per week of wiener casings proved to be quite a challenge. The casings are a cellophane-like material housing millions of wieners as they travel through the smoke and cooking process. This cellophane-like casing is stripped away from the wieners prior to packaging and shipping.
The casings are segregated from Kraft's waste stream at the plant, then processed through a grinder that reduces their size from as large as 140' by 3" to approximately 2" segments prior to depositing them in a forty cubic yard trash compactor. The casings are then transported to the compost facility. This occurs three times per week with each container weighing approximately 12 tons. Prior to grinding, the casings look like cooked spaghetti, all tied together.
The composition of the casings is primarily cellulose and water, with small amounts of glycerin and propylene glycol. Critical to rapid composting are the variables of proper carbon/nitrogen ratio, aeration, moisture content, and particle size. Casings have sufficient carbon and some water, but are missing nitrogen and a bulking agent for aeration. However, this material is certainly compostable. The ideal carbon to nitrogen ratio for bacterial decomposition is 30:1. Primarily carbon, the wiener casings will decompose, but very slowly. Casings mixed with a nitrogen source will decompose more rapidly.
To enhance the decomposition process, casings are mixed with ground yard waste. The yard waste (comprised mostly of grass, leaves, and brush, and clean drywall) provides some valuable nitrogen, but perhaps more importantly, it acts as a bulking agent to improve the porosity. Porosity is necessary for aeration, which directly affects the time it takes for organics to decompose and its potential for odors.
Casings are laid down adjacent to windrows of yard waste. Using a wheel loader, yard waste is folded over and into the casings producing a 50:50 ratio of yard waste and casings by weight.
The inclusion of wiener casings into the compost facility has required major operational changes. Before the inclusion of casings, the composting operation was primarily passive, with minimal turning and watering, as there was abundant site processing capacity. The annual addition of 1,664 tons of material has caused the adoption of more active composting methods to assure site processing capacity is not exceeded. Windrows of a 50/50 mixture of mulch and casings are turned and watered weekly to enhance decomposition and minimize odors. Finished compost product is produced in 4-6 months.
Initial questions arose as to what impact the cellulose casings might have on the environmental quality of the compost, the facility, and the surrounding area. Analyses by Toxicity Characteristic Leaching Process (TCLP) for Metals, Volatile Organics, Semi-volatile Organics, Pesticides and Herbicides were performed on compost grab samples. No pesticides, volatile organics, or heavy metals were detected in the finished product.
Results from samples taken from storm waste basin, in accordance with the site's NPDES permit, showed no exceedance of the effluent discharge limitations.
Soil nutrient analysis and germination tests were performed on separate compost samples aged from 1 week, 4 months, and 6-8 months by the University of Missouri-Columbia Soil and Plant Testing Lab. Electrical conductivity was observed as relatively high (6-10 mmho/cm) from the soil analysis. This is an indication of salinity, which should not be a limiting factor in the use of the compost as a soil amendment. All remaining results were well within expected levels for standard compost.
Germination tests results indicated finished casing/yard waste compost would have no negative effects on plants. Seedlings developed in the compost as well or better than in the control sample.
The initial casings received during the first few months have been fully composted and have been used on the landfill to establish vegetation. We are confident of the continued successful composting of these materials into a high quality soil amendment.
Columbia's Compost Facility has nearly a decade of operational history. It is hard to say where the next decade will lead. It is also hard to imagine a more interesting compost project than hot dog dirt, but you never know what's going to turn up.
To contact Richard Wieman, call 573-874-6298 or send e-mail to email@example.com.