July 1, 2004 | General


BioCycle July 2004, Vol. 45, No. 7, p. 38
Area businesses and schools partner with King County Solid Waste Division to recycle residuals and lower disposal costs.
Kinley Deller

KING County, Washington’s Solid Waste Division is evaluating the feasibility of on-site, in-vessel commercial food residuals composting. The pilot program – which is assisting 13 schools and businesses in acquiring and using the small units – will provide data for those interested in initiating similar programs. Partially funded by a grant from the Washington State Department of Ecology (DOE) last year, the project primarily focuses on two systems: the BioStack/Advanced BioSystem and the Earth Tub.
A targeted promotional campaign was used to get the program underway. Creative ads asking the question “Got Food Waste?” were run in local business journals. A brochure describing the advantages of on-site composting and an overview of the available assistance for pilot participants was mailed to targeted businesses within King County, such as restaurants, caterers, assisted living communities, food processors, wineries, grocery stores, food banks, colleges, resorts, hotels and large corporations. Articles appeared in a number of local papers. As a result of the campaign, over 60 businesses contacted the Solid Waste Division asking for additional information. Interested businesses received a site visit to assess the location and food residuals of the business, explain program details and answer any questions. Criteria for participation included having a dedicated person in charge of the unit, sufficient staffing, space to locate a system, low meat content of food scraps, and management support. Seven businesses signed partnership agreements to participate.
After start-up of the business phase of the program, additional promotion was done to recruit schools. The promotion was conducted via word of mouth and by direct contact with teachers who had worm bins in their classrooms or had invited a Solid Waste Division speaker to talk to students about composting. Six schools have joined the program.
When meeting with businesses and schools about getting involved in the program, Solid Waste Division staff often began by explaining that, on average, a 55-gallon container of food residuals weighs about 400 pounds. For businesses and schools that utilize a compactor and pay for garbage disposal by weight, this quickly impressed upon them the potential cost savings that could be obtained by no longer adding food residuals to their compactor, especially when it meant they could go longer between compactor pulls. Also discussed were the facts that in-vessel systems often have fewer odor issues than leaky dumpsters, lower sewer maintenance costs, and produce a mulch or soil that can be used for landscaping. And because food residuals make up 14.6 percent of the solid waste stream in King County, utilizing this resource for a higher use can effectively reduce the overall amount of material being landfilled.
The Solid Waste Division covered significant portions of the purchase price of the composting systems (75 percent of the cost for businesses and 87.5 percent of the cost for schools and nonprofits). The contracted price, including shipping, for the BioStack was $1,976.34. The contracted price, including shipping and installation for the Earth Tub, was $8,875. The DOE grant was used to offset the Solid Waste Division’s portion of the costs on a few of the systems which allowed more businesses and schools to take part in the pilot program. Participants were limited to the purchase of only one system. Additional technical assistance included selecting the best type of system based on site-specific characteristics, start-up, training staff to operate the system, and providing instructional signs.
In return for the Solid Waste Division’s financial and technical assistance, program participants are required to compile data for three years on the daily use of their system including documentation of food residuals diversion rates, compost generation rates, and comments/issues that arise as the system is being used (odors, staffing problems, etc.). Data sheets are provided and returned to the Solid Waste Division on a regular basis. Quarterly verbal reports and an annual brief written update are required. Finally, the participants have agreed to allow photographs and video of the systems for purposes of documenting and promoting the pilot program.
Participating businesses and schools also are required to pay for the portion of initial capital costs not covered by the Solid Waste Division, pay for any associated operating costs and commit to providing staff time for operating the systems. Three people at each pilot program participant location must sign a “Partnership Pledge” stating they will comply with the requirements of the program.
Made by Biosystem Solutions, the BioStack unit is a flow-through vermicomposting system that can reportedly process 20 lbs/day of food residuals. BioStacks have been installed at six locations as a part of the pilot program: King Street Center (office building), My Favorite Caterer (caterer), Lake Washington Technical College, Aegis of Shoreline (assisted living community), Wild Mountain Café (restaurant), and Briarwood Elementary School.
Made by Green Mountain Technologies, the Earth Tub is designed specifically to compost food residuals on-site and can reportedly process up to 150 lbs/per day. Earth Tubs are being installed at five locations: Bernie and Boys Market (grocery store), Willows Lodge (resort), Crestwood Elementary School, Waskowitz Outdoor Education Center, and Pacific Crest Farm (school-owned farm).
The Solid Waste Division also has assisted pilot program partners in acquiring smaller systems if they seemed better suited to the needs of the business or school. Schuller’s Bakery is using a standard vermicompost plywood box for composting their preconsumer food scraps and the Evergreen School is using a standard WigWam for composting its lunch food scraps.
At this point (end of June), 11 of the units have begun operation. Table 1 shows the amount of food scraps being diverted at seven of the locations. The percentage of total waste diverted varies dramatically between the different businesses/schools.
In addition to learning about the quantities of food scraps that can be diverted and the amount of compost that can be generated, the pilot program seeks information on the kinds of technical issues that arise with in-vessel composting systems. Some issues are specific to the systems used while others may be common to any type of food composting system. For example, users of the BioStack system like its small footprint, security (lockable doors), ease of use and the flow-through vermicomposting technology. Some concerns have been expressed over the amount of leachate that accumulates in the compost collection drawers. Leachate generation may be caused by several factors, including minimal ventilation (the county did not purchase the optional climate control attachment), inadequate amount of bedding material, and exceeding the food feed rate capacity.
The leachate would not be an issue except that it mixes with compost that has fallen down into the collection drawer, creating a slurry that can go anaerobic if not quickly emptied. The Solid Waste Division program manager, with input from the pilot participants, solved this problem by placing a collapsible window screen or a raised piece of stiff hardware cloth in the bottom of each drawer to keep the finished compost separated from the leachate so that the leachate can be sucked out of the bottom of the drawer using a turkey baster – a rather crude yet successful solution.
Other challenges that have arisen and been solved include flies (controlled by placing solid sheets of newspaper over the top of the bedding in each drawer), bad odors (went away when leachate was dumped more often), and leachate dripping occasionally from the drawers when they are pulled out (reduced when leachate is emptied regularly and not an issue when system is placed outside on soil). Despite these few glitches, all participants continue to use their BioStacks.
To date, only two of the five Earth Tubs being purchased as a part of the Solid Waste Division pilot program have been operating, so experience is limited. However, users of the system thus far have been impressed with the amount of food residuals that can be added, the appearance of the system, and the fact that the biofilter works well for keeping odors down. The biggest problem with the Earth Tubs so far has been for the schools to get a school district electrician to come to their site and connect the system.
Another challenge has been convincing the users that they really do need to put in as much bulking agent (usually wood shavings) as recommended by the manufacturer and the Solid Waste Division. When not enough bulking agent is added, the contents of the tub get high in nitrogen and very low in available oxygen. The contents are thereby not able to start active composting and begin to ferment or go anaerobic. When filled close to the brim with wet food residuals and not much bulking agent, the liquid in the tub is not able to evaporate or drain, resulting in a wet, odorous mass. This only happened once and provided a great learning opportunity for the pilot program participant and Solid Waste Division staff assisting with the program. The need to add enough bulking agent for the Earth Tub systems cannot be overlooked.
There have been occasional user errors, such as adding inappropriate materials – e.g., corn stalks, large bread bags and a coat hanger – that wrapped around the auger. Despite the learning opportunities they have experienced in familiarizing themselves with the system, both current users of Earth Tubs are generally happy with their systems and continuing to enthusiastically fill them up with food scraps.
It is still too early in the program to accurately assess the feasibility of on-site food residuals composting systems for businesses and schools in greater King County. The pilot program has, however, already been very valuable in revealing the challenges and rewards of managing relatively small-scale, in-vessel composting systems. The most important lesson learned so far is that correct use of the composting equipment can prevent most of the perceived drawbacks of food residuals composting. As each technology has its own limitations and operating requirements, it is critical that the users get the initial hands-on assistance necessary for them to effectively use their system. King County will continue to compile the data from this pilot program and make it available to anyone interested.
Kinley Deller is with the King County, Washington Solid Waste Division and can be emailed at:

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