The majority of food waste is disposed of through the use of in-sink garbage disposals, using over 3 million gallons of water per year in Burton dining hall alone. This wastewater is then treated at the Northfield sewage treatment plant; the cost of this treatment is expected to rise as more strain is placed on the facility. With the construction of a new dining hall on campus, Carleton is reevaluating its use of in-sink garbage disposals. Facilities staff and concerned students have collected data on alternate methods of food waste disposal to locate a more economically and environmentally efficient system. This analysis compares the costs and benefits of continuing the in-sink method, composting using on-site windrows, transporting food to a composting facility in Rosemount, reprocessing of food waste for animal feed, and forming a composting partnership with St. Olaf.

In Sink Garbage Disposal

Currently, post-consumer food waste is washed down garbage disposals in the dishrooms. Most pre-consumer food waste (fruit and vegetable peels, etc.) is taken to the Rice County landfill. Because it is necessary to scrape plates before they are put in the dishwasher regardless of food disposal method, there is no extra labor cost required in scraping food into the disposals. Costs associated with the use of garbage disposals are minimal, as water costs $0.75 per one hundred cubic feet, and wastewater costs $1.44 per one hundred cubic feet. Although the amount of water used by the disposals proved difficult to quantify, Facilities roughly estimated it by subtracting the amount water used in Watson from that used in Burton, because the resident student population is comparable in the two dormitories. This calculation results in 400,000 cubic feet per year (3,000,000 gallons), which would amount to a total cost of only $8760. Facilities estimates the cost of in-sink garbage disposal at about $8,500 per year.

On-Site Composting with Passively Aerated Windrows

Passively aerated windrow composting systems are used by several schools throughout the country. In this system, food waste is mixed with low grade paper products and other materials (often wood chips, yard waste, or manure) and placed in rows underlain by PVC piping to deliver air to the inner pile. The cost of this system varies greatly from college to college. The system implemented at Middlebury College in Vermont has cost about $48,000 since April 1993. Their estimated average cost per ton is $43, as opposed to $135 per ton to landfill waste. This has resulted in great savings for the college. Recently, St. Olaf College also investigated the costs of an aerated windrow system. They estimated the start up and maintenance costs at $542,789. This estimate accounts for equipment, building costs, electricity, site maintenance, engineering, and licensing. At Carleton, the cost of such a system has yet to be thoroughly investigated. However, it would probably be more expensive to implement at Carleton than at St. Olaf because of differences in soil structure. This system would require a large initial investment; however, the costs would presumably decline over time, with the upkeep costing less per ton than other systems because transportation and storage needs are reduced.

Hauling to Composting Site in Rosemount

Transporting food waste to SKB, a private composting facility in Dakota County is an option for off-site composting. The waste would be hauled weekly. In addition to transportation costs of $200/trip, there is a $45 tipping fee for each ton. Leasing a compactor for food storage would cost an additional $3600 annually. Assuming two tons of waste per week for the 36 weeks of the year that the dining halls operate results in a total annual cost of $14,040. While composting food waste is more environmentally preferable than the current system, hauling the food to Rosemount weekly would use additional fossil fuels, a negative ecological impact that should also be considered.

Reprocessing of Food Waste for Use as Animal Feed

Endres Processing in Rosemount, Minnesota is a company that uses food waste to create feed for cattle, hogs, and poultry. Endres currently contracts with over 100 different food waste sources and has recently added restaurant style food waste to their operation. It is likely the largest such facility in the country and has been in operation for about twelve years. Endres charges restaurant style suppliers $50 per ton. If Carleton were to contract with Endres, it would be stored in containers provided free of charge by the company and hauled away on a biweekly basis. As Carleton produces about two tons of food waste per week in Burton dining hall, this amounts to a yearly cost of $3,000. From an ecological standpoint, this option is preferable to composting because the final product is put to a higher use. Additionally, this option is both more cost efficient and ecologically sound than the current method of disposal.

In-Vessel System

This option, although regarded as a greater financial investment, reduces space necessary and is a much faster process than traditional composting methods. Essentially, food waste is placed in a large bin and is composted in 20 to 30 days. After that point a space investment is still necessary for curing. This is the option that St. Olaf College and Northfield Hospital are adopting. A partnership with the two institutions, assuming Carleton would produce 37.5% of the waste stream, would be $30,400 (based on operating costs of $22,500 and daily pick-up costs of $7,900 annually). Additionally, Carleton's share of the start-up costs would be $225,000. This is a constant value, assuming Carleton produces roughly 1/3 of the waste, and does not specify pounds/meal.