BioCycle December 2006, Vol. 47, No. 12, p. 26
As the marketplace develops, competitors offer lower hauling fees to businesses with higher percentages of compostables.
SAN JOSE, CALIFORNIA boosts reuse by waiving a $13/ton disposal tax, a $3.49/cubic yard franchise fee, and a 50 cent AB939 state recycling fee for loads bound for recycling or composting facilities. These fees must be paid for waste destined for the landfill. Haulers compete in an open market subject to constant competition.
Two years ago, more than 40,600 tons of organics were collected from San Jose businesses. The bulk of that material was composted at Allied Waste/BFI in San Jose or at Z-Best in Gilroy. Table 1 gives details on collection methods and tonnages at the two facilities.
BFI Newby Island Organics (now part of Allied Waste) began composting food-rich loads in 1999 in response to requests from managers of restaurants and grocery stores. “The marketplace was developing and our competitors were offering lower hauling fees to businesses with high percentages of compostable waste,” says Hilary Gans, Organics Market Development Manager at Allied/BFI. As an additional incentive, the City awarded the company funds for a demonstration project to explore the economic and technical feasibility of composting organic materials collected from businesses. A 1998 study had shown that 24 percent of the material being buried in landfills was food scraps and other organic materials.
Allied/BFI began composting of food-rich loads in a Green Mountain Technologies (GMT) Containerized Compost System. (www.gmt-organic.com) The system included four rectangular stainless-steel structures, similar in size and appearance to a 40 cubic-yard roll-off garbage bin to hold the collected material. It also provided for automated aeration.
Hauling customers were not required to separate compostables from refuse. The operators wanted to test the feasibility of composting the mixed material and screening contaminants out of the finished compost. Despite screening to a half-inch, glass and plastic film persisted in the finished product. Lacking markets, the material was spread on the working face of the landfill as Alternate Daily Cover (ADC) at the end of each day.
At the same time, demand for the composting program exceeded the capacity of the GMT containers. Allied/BFI shut down the business composting program for a year while securing permits for composting of source separated organics in open windrows. All food, including meat and bones, is accepted along with soiled paper, wax-coated cardboard cartons and plant debris. Sales representatives estimate the percentage of compostables in customer’s refuse and check for space to accommodate a collection container dedicated to organics. Hauling rates are negotiated based on diversion potential and route density. About 30 percent of the businesses that begin the program are unable to adequately separate the compostables from the refuse and are dropped from the program.
Allied/BFI requires customers to put biodegradable materials into clear plastic nonbiodegradable bags so the contents are visible to employees. To remove the bags, material is run through a 6-inch trommel screen mounted with knives that break the bags, releasing the material onto a conveyor that runs below the screen. The bags are screened out before the compost is sold.
Material is then ground and mixed with yard trimmings at a ratio of 70 percent yard trimmings to 30 percent food scraps/soiled paper and put in windrows for 30 days. It is kept moist with a watering truck but is not turned during this period due to potential release of odors. At the end of the 30 days, it is mixed with windrows from the residential yard trimmings collection. The resulting windrows are turned twice weekly with a Scarab, kept moist with a watering truck and composted for an additional 50 days. Finished compost is screened to remove oversize particles and contaminants and is sold to the landscaping and agricultural industries as well as soil blenders and is distributed to city parks.
DIFFERENT APPROACHES TO COMPOSTING
Collection and composting systems at Z-Best in Gilroy are very different. Rather than source separated collection, food-rich loads from restaurants, grocery stores and other businesses are processed to remove contaminants. The material runs through a bag-breaker, then across sort lines to remove recyclables and contaminants. Eight percent of incoming material is recycled as cardboard, glass and metal, and 15 percent is removed because it is not suitable for composting.
Material is then run through a grinder and loaded into a bagging machine, which packs it into eight-mil laminated plastic composting bags that are 10-feet in diameter and 200 feet long. Two aeration pipes run the length of each bag. They are connected to a timer-controlled air blower that maintains aerobic conditions. Optimum temperature and moisture conditions are maintained by managing the blower operating time and venting the water vapor during the composting process. Venting is accomplished by cutting openings in the bag to decrease moisture in the mixture, and closing the openings when the mix gets too dry.
Each bag holds about 200 tons of feedstock. After 14 weeks, the bag is cut open and the compost is managed in open windrows for two to three weeks prior to screening and curing.
Compost is cured for a minimum of eight to 12 weeks. Depending on markets, it is screened to 5/16 or 1/8 inch. The 1/8 inch material is called “topdress compost.” Alex Sharpe, Z-Best Compost Facility Marketing Manager, is hopeful it will find a niche as topdressing for turf and golf courses. It is also blended with yard trimmings compost and sold for landscape use. The oversize material, about seven percent of the total, is used for alternative daily cover for a landfill. Approximately 30 percent of the incoming tonnage is lost as moisture during the composting process.
Karin Grobe, based in Santa Cruz, California, consults and does outreach and communications in the fields of vermicomposting, home composting and overall organics recycling. Her e-mail is firstname.lastname@example.org.