BioCycle January 2010, Vol. 51, No. 1, p. 22
Farm composter in Massachusetts solves odor and capacity problems by building a rotary drum to preprocess food waste from commercial and institutional generators.
THE decade long program of the Massachusetts Department of Environmental Protection (DEP) to promote diversion of commercial food waste to composting has significantly increased quantities of source separated organic materials being diverted across the state. Most of the major supermarket chains participate, as well as a growing number of restaurants, convention centers, schools and colleges. One of the most aggressive is the City of Cambridge’s commercial organics collection program (see “Partnerships Move Commercial Organics Collection Forward,” August 2007), which works with Save That Stuff, a local hauler.
One recipient of organic waste generated in Boston and Cambridge is Rocky Hill Farm (RHF) in Saugus, Massachusetts, approximately 10 miles north of Boston. The former pig farm has been successfully processing food waste for over ten years, but as the quantity of materials increased, RHF found its site to be constraining, and occasional odors were reported to the local Board of Health.
To assist the farm in handling food waste, DEP, with partial funding from the US EPA, provided a technical assistance grant to RHF in 2007 to evaluate its operation and review in-vessel composting technologies. City Soil & Greenhouse Co. of Boston, who had done an earlier technical assistance program at the farm with DEP funds, was again selected to perform the work.
Fran and Maryanne Buzun, owners of Rocky Hill, actively participated in the technical assistance project, and visited a number of operating in-vessel facilities. Ultimately, the Buzuns decided to use their family’s Yankee ingenuity to design and build their own rotary drum composter, a technology that the City Soil & Greenhouse Co.’s technical assistance report identified as a potentially cost-effective investment.
PROCESSING, PRODUCT QUALITY BENEFITS
Starting with a five-eighth-inch thick, 11-foot diameter steel drum formerly used to dry rock at an asphalt plant, Fran Buzun and crew added a 37.5 foot section to increase total length to 53 feet, providing processing capacity of 20 cubic yards/day with a 3-day retention time in the vessel. A 3 HP motor and chain drive provides four revolutions per hour. A mixture of two parts yard trimmings to one part food waste is loaded into a hopper, and then conveyed through a feed chute. Four inches of polyurethane spray insulation effectively maintains temperatures of 140°F to 150°F in the outdoor rotary drum, even in subfreezing conditions. A variable speed fan was installed at the inlet to the drum. It draws air from the discharge end through the composting mass, counter to the flow of material.
After almost 12 months of operating the rotary drum, Buzun outlines the major benefits to his operation. “We reduced the volume of material to be processed in outdoor windrows by almost two-thirds, considering that 20 cy of material loaded into the drum becomes approximately 7 cy of compost when discharged in three to four days,” he explains. “We’ve also increased site capacity by shortening the amount of time material is kept in outdoor windrows on the compost pad due to faster rates of degradation.”
Odors have been reduced due to decomposition of putrescible material in the rotary drum prior to outdoor composting. There is also reduced leachate generation on the composting pad. Compost product quality has improved as there is greater reduction in particle size of organic waste in the rotary drum compared to turning windrows with a front-end-loader.
Supplemented by a low interest loan of $150,000 from the Massachusetts Recycling Loan Fund, Buzun estimates total project costs to be approximately $200,000, including extension of electrical transmission lines, concrete pad, rotary drum and drive system, feed hopper, two conveyors, exhaust air fan and labor. “We’re looking at starting to run the exhaust from the drum’s variable speed fan through a biofilter in order to remove more moisture from the drum and provide another level of odor control,” adds Buzun. “I’d also like to install a trommel screen on the discharge end of the drum, which would facilitate recycling of over-sized organic matter back through the drum, and remove a portion of the inorganic contaminants prior to windrow curing.”
Sumner Martinson, DEP’s Director of Composting, praises the Buzuns for implementing the recommendations of the technical assistance report. “Rocky Hill Farm really did their homework, and followed through with constructing what appears to be a very robust rotary drum which will hopefully keep them operating for many years to come,” he says. “They are a model of how DEP sees the food waste composting industry evolving in the next decade.”
Robert Spencer, a BioCycle Contributing Editor, is an environmental planner specializing in compost facility development and operation. He worked with City Soil & Greenhouse Co. on the most recent technical assistance project at Rocky Hill Farm, and is based in Vernon, Vermont (email@example.com).
January 19, 2010 | General
On-Farm Composting With Yankee Ingenuity
BioCycle January 2010, Vol. 51, No. 1, p. 22