"Innovations" Case Studies: Organics Options

Discarded Food and Collection

• Discarded Foods
• Residential Discarded Food Collection
• Commercial Discarded Food Collection

Discarded Foods

Discarded food and food-contaminated paper (sometimes referred to as “soiled” paper) constitutes 10 to 15 percent of the residential waste stream of many communities. Food waste is the single largest waste stream remaining after the community has implemented basic curbside, yard trimmings, and construction and demolition (C&D) debris recycling programs.

There is no one strategy for diverting discarded foods to beneficial uses. Food can be donated to charities, converted into animal feed, rendered into soap or other products, and composted. Clearly the donation of edible food to charities is the highest and best use of this resource. If food is disposed of as waste, it can be collected and recycled in a number of ways.

One of the major considerations at present in California is the availability of processing systems to handle different types of discarded foods. Most composting facilities that were established primarily to accept yard trimmings are not permitted or designed to accept all discarded foods. Some of those facilities may be able to accept produce wastes, but not meat and grease. Communities should contact their local enforcement agencies to identify the permit status of composting facilities in their area.

Four basic types of composting approaches are in use in California:

• Passive static pile composting
• Turned windrow pile composting
• In-vessel composting
• Vermicomposting

Static piles are suited for small operations but usually cannot accommodate meat or grease. Aerated windrows can handle meat and grease with frequent turning and careful temperature and moisture control, although this is not advisable in many circumstances. In-vessel composters are enclosed temperature and moisture-controlled systems. They come in a variety of sizes and have some type of mechanical mixing or aerating system.

In-vessel composting can process larger quantities in a relatively small area more quickly than windrow composting and can accommodate animal products. Vermicomposting uses worms (usually red worms) to break down organic material into a higher biologically active compost (worm castings). It cannot accommodate animal products or grease.

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Residential Discarded Food Collection

Much of the progress in the collection of separated discarded food has been in the Netherlands, Germany, Switzerland, and other European countries to date. In the Netherlands, virtually all municipal governments provide source-separated collection of all residential organics. Both yard and discarded foods are generally collected on at least a biweekly basis.

The European experience has been motivated, in part, by the absence of garbage disposals in most residences and by the adoption of aggressive national environmental policies.

A national environmental policy adopted in the Netherlands in 1994 requires that all municipalities collect residential organics separately. Those materials are banned from landfills. The Netherlands has also adopted a goal of achieving 75 percent waste diversion from landfills and incinerators.

In residential programs that already have a weekly yard trimmings pickup by rolling carts, adding food can increase diversion without adding significantly to costs. The key to this is whether the current composting facility can accept discarded foods. Additional start-up costs may be incurred for kitchen pails and outreach. Additional costs may be incurred for adding cart service. These may be offset by savings in collection efficiencies and avoided disposal costs.

One of the major issues for instituting discarded food collection programs is the type of storage containers to be used, both in the kitchen and outside the house. Discarded food is generally stored in the kitchen in a temporary storage container. This may be a special container provided to residents by the recycling program, a plate, a used coffee can, or a used 1-gallon plastic ice cream container with a lid that residents provide themselves.

The storage container is usually stored in a convenient place, such as a countertop, under the sink, or in the refrigerator (to reduce the generation of odors). Residents are generally asked to empty their plate or container into their yard trimmings cart and to close the lid of that cart. Residents are encouraged to empty their container in the cart frequently and then place their plate or container in their dishwasher immediately. This keeps counters clear of food debris and smells, and it also minimizes the potential for pests.

Residents are asked to place food-contaminated paper into these same bags and place them in the yard trimmings bin as well. By combining both discarded food and contaminated paper together, the paper will absorb the moisture from the discarded food. Acceptable materials might include:

• Fruit and vegetable peelings and scraps
• Meat and fish bones and scraps
• Egg shells, cheese, and dairy
• Grains or breads
• Used paper towels, napkins, and tissues
• All food leftovers
• Food-contaminated cardboard packaging

Plastic-coated or wax-coated papers or bags (for example, milk cartons, juice boxes, ice cream cartons, frozen food containers, food takeout containers, margarine, butter, or candy wrappers).

Based on programs around the world and pilots in North America, programs that collect discarded food in this way should be able to obtain a weekly setout rate of 30 to 50 percent.

Those participating will generally provide 80 percent of their discarded food and food-contaminated paper. The result of adding this material to a yard trimmings program should therefore yield diversion of another 3 to 6 percent of the total residential waste stream once the program is operating.

The City of Dixon, Calif., added discarded food (initially fruits and vegetables only) to its yard trimmings program in April 1997. The program serves 4,000 households on a weekly basis and provides a white plastic pail with handle and lid to residents on request only. These are generally given out at speaking engagements. Participants have had no problems with pests.

As noted with Riverside, Dixon had no curbside recycling when this program began. The city decided to collect yard trimmings first. Dixon was able to move forward with this innovative program due to the leadership of the B&J Landfill (a Norcal Waste Systems company). B&J installed one of the first “Ag-Bag” in-vessel composting systems in the state as a demonstration project under the registration tier of their compost permit.

B&J applied for and received a composting permit to provide ongoing service, not only for produce, but also for all discarded foods (including meat and grease). Because of its leadership, this facility was able to expand its operations to accept discarded foods from its sister Norcal company in San Francisco. That program is described in detail in CIWMB Publication #310-02-001, “Food Waste Recovery: A Model for Local Government Recycling and Waste Reduction.”

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Commercial Discarded Food Collection

On-Site Composting

During the past several years, new in-vessel and enclosed composting systems have been developed for use in many commercial applications. These systems enable businesses and institutions to compost on-site. This saves collection costs, which are typically 80 percent of the costs of solid waste management.

These systems reportedly cost between $30 to $50 per ton to operate, a cost that is competitive with most landfill tipping fees in California. The capital costs for these systems can be easily amortized by businesses that calculate the substantial avoided collection and disposal costs.

The Earth Tub from Green Mountain Technologies (shown below) is an example of one type of available system. The Earth Tub is a fully enclosed composting vessel featuring power mixing, compost aeration, temperature control, and biofiltration of all process air. This self-contained unit is ideal for small-scale composting at schools, universities, restaurants, hospitals and supermarkets. The picture below shows an Earth Tub from Green Mountain Technologies.

The Earth Tub’s capacity is about 150 pounds/day, and the auger will shred and mix a ton or more of compost in 10 to 15 minutes. During active composting, the Earth Tub should be mixed at least two times per week. The volume reduction is typically 70 percent or higher. Compost produced is often used as a thin mulch around facility grounds, or bagged and distributed to customers and employees. The compost can be cured for 20 to 40 days for further stabilization.

Maintaining aerobic conditions and controlling temperature are essential for composting and odor control. The aeration system draws air through the compost and forces the exhaust air through our biofiltration air purification system to remove odors. Liquids are collected and disposed to a sanitary sewer or holding tank.

For larger applications handling 1 to 150 tons per day of organics, Green Mountain Technologies offers its CompTainer composting vessel. Materials are loaded into a compost mixer, blended, and loaded into the CompTainer.

The CompTainer has a stainless steel aeration floor to evenly distribute pressurized air while capturing leachate. Once full, the operator closes the CompTainer, attaches the aeration lines and inserts the temperature probes.

The CompTainer regulates sterilization during 10 to 24 days of active composting. The CompTainer can be picked up by a standard rolloff truck and dumped at a product storage area or at its final application. The compost may be screened to recover bulking agent and to refine the compost product.

Although composting products are available, they are just beginning to be used in different California applications. One of the constraints appears to be the lack of technically knowledgeable people at businesses to oversee such operations.

This presents a business opportunity that may be filled in the future by service companies willing to finance, place, and maintain such units at interested companies. Communities could assist in funding the startup of such service companies or help promote the in-vessel equipment directly to appropriate businesses.

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Vermicomposting

Vermicomposting refers to the controlled degradation of organic materials primarily by worms. It is the deliberate attempt to grow and maintain a large population of worms that distinguishes vermicomposting from other conventional thermophilic (heat-producing) composting. Composting worms are capable of ingesting one-fourth to two times their body weight in food each day, depending on variations in temperature, pH, and environmental conditions.

In vermicomposting, worms obtain their nutrition from microorganisms consuming decaying organic matter. As worms multiply, they can consume more material. Their population grows and stabilizes according to the availability of food.

Worm feeding also increases the surface area of the material being treated, thus increasing microbial growth. As this process continues, complex changes occur. The process eventually produces a finely structured material known as worm castings, or vermicompost. Worm castings are suitable as both a plant growth medium and an agricultural soil amendment.

Worm boxes

Worm boxes have become popular as one method for safely composting food scraps at home, schools, and offices.

Popularized by books such as Worms Eat My Garbage and The Worm Book, home vermicomposting is now practiced in more than a million homes throughout North America. Some communities subsidize the purchase of home worm bins as another option for home composting.

Worm bins come in all shapes and sizes, such as the 100 percent plastic “Worm Barn” and the wooden “Worm Cabana” available from Yelm Worms. The picture below shows a Worm Cabana made by Yelm Worms.

Larger worm bins are now being manufactured for use in commercial and institutional settings, including cafeterias, restaurants, campuses, and nurseries. The picture below shows a Worm Wigwam made by Yelm Worms.

The Worm Wigwam from Yelm Worms, measuring 5 by 6 feet, is a large-scale continuous-flow worm bin. It is designed to handle at least 75 pounds of food and bedding every day. Completely covered and verminproof, this system efficiently composts discarded foods and mechanically harvests worm castings.

Produce Collection

Source-separated produce from groceries and food processors is increasingly collected around California. One of the largest examples of produce collection is the system pioneered by Community Recycling and Resource Recovery.

Community Recycling serves more than 1,000 grocery stores throughout the state, including all the Safeway supermarkets. Crew members mix the discarded foods with yard trimmings at the company’s composting site near Bakersfield. More details on these systems are available in CIWMB Publication #310-02-001, “Food Waste Recovery: A Model for Local Government Recycling and Waste Reduction."

Animal Feed

Inedible food can be used directly to feed animals or blended and processed to produce animal feed. This method can produce a large amount of waste diversion in a comprehensive program. San Francisco diverts more than 21,000 tons per year from the waste stream through animal feed (including rendering).

Four rendering companies serving San Francisco collect food service grease and meat for rendering products. Dext Feed from Stockton collects discarded bread, flour, and other dried bakery products and makes animal feed products.

A dairy farmer from Sonoma County picks up the inedible or spoiled produce from the San Francisco Food Bank free of charge. He blends the organics into his dairy and heifer feed (using up to 10 percent produce in his mix). He also sells the material to other farmers in the area. More than 400 tons per year of inedible produce has been productively used for dairy and cattle feed.

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Last updated: October 26, 2007