January 24, 2008 | General

In-Vessel Option For On-Site Food Waste Composting

BioCycle January 2008, Vol. 49, No. 1, p. 35
A Toyota manufacturing plant in Kentucky has an on-site unit to process food waste from six cafeterias. Smaller drums are used at universities and correctional facilities.
Robert Spencer

For more than 30 years each, John Willis and Bernie Beers have been in the business of supplying equipment and services to farms in Texas, from grain silos, to feed systems, to manure hauling and land application. As they traveled around the state, with Willis piloting his own airplane much of the time, it was the waste management aspect of the business that seemed to be the area of greatest need and potential growth, from the Panhandle to the southeastern region. Therefore, around 1990, Willis and Beers formed BW Organics (BWO) for the purpose of designing and manufacturing rotary drum vessels to use for composting manure and other agricultural by-products such as animal mortalities and paunch. Little did they realize that 15 years later, they would have over 100 drums throughout the world processing a wide range of materials.
The drums are available in eight different sizes, with processing capacities from 0.33 cubic yards (cy)/day to 32 cy/day, and a corresponding price range from $8,100 to $179,000. The most common application of the BWO drums is for manure, including poultry, dairy, cattle and hog farms. For a sense of scale, a 16 cy/day unit can handle dairy manure from 300 to 500 milking cows.
For the last few years, BW Organics has experienced a strong surge in use of its rotary drum for composting food waste at correctional facilities, colleges and industrial cafeterias. A number of locations took advantage of the company’s mobile pilot compost unit to test out their own material in a rotary drum before making a decision to purchase one. “We have a portable unit that can process about 1 cy/day that some of our customers will rent so they can try different recipes, and get a better estimate of how large a drum they may need,” says Beers. “This helps once the unit they buy is ready to start up because they get experience with recipes based on their own organic inputs.”
Among the clients who tried out and then purchased a unit was the Toyota Motor Manufacturing Kentucky, Inc. (TMMK) factory in Georgetown, Kentucky. Situated on a 1,400-acre campus, the Toyota facility employs over 10,000 people, including contractors and other nonmanufacturing personnel. There are six employee cafeterias, as well as substantial landscaping operations. The facility, Toyota’s largest outside of Japan, manufactures the Camry, one of the best selling cars in North America.
In 2005, the TMMK plant was designated a zero landfill facility, which specifies that all waste produced on site is either recycled or reused, and nothing is shipped to landfills. The goal is 95 percent or better diversion from the landfill, including waste-to-energy. One component of the recycling system is a rotary drum, which is used to compost food waste and landscaping materials. Following almost six months of pilot composting with the mobile BWO drum, TMMK purchased the Model 840, an 8-foot by 24-foot unit, and installed it on a 46-foot by 70-foot concrete pad, inside a two-sided pole barn.
The pad was designed to accommodate an additional drum, plus a shredder and a mixer; the building protects workers from the elements. The shredder breaks the waste up into fist-size pieces, which are then conveyed to a mixer, and then to the rotary drum. Typical retention time is 7 to 10 days, followed by composting in outdoor windrows for further curing. A custom-made rotary screen with 1.5-inch openings is used to screen out the inorganic contaminants such as cans and plastic bottles. The compost is then ready for use in landscaping of the grounds, the 20-acre vegetable garden or the geodesic dome greenhouse.
Chuck Martin, Facility Control Specialist at TMMK, explains that it was the BWO composter that allowed the facility to get the zero waste designation. “We process food waste and soiled paper from the six cafeterias, break rooms and janitorial operations, as well as landscaping debris,” he says. “In each of the cafeterias we have ‘Earth Care Centers’ where employees recycle their bottles and cans, as well as their compostable materials. We constructed countertops with holes cut out for each material to be put into receptacles under the counter, and use labels and pictures to show what materials are being recycled at each receptacle. In the kitchens we also recycle our organics, as well as containers.”
Barrels used to collect food waste are lined with biodegradable plastic bags. The food waste is then shredded and mixed with paper towels and office paper. “We can push the composter to the limits and if we leave the material in the drum for 14 days the compost is almost complete. Typically, we run a 7 to 10 day cycle, loading and discharging each day,” he adds. Instead of having the drum rotate constantly, they installed it with a timer that turns it a couple of revolutions each day to mix the material.
Total cost for the composting system and other equipment was about $90,000. “Payback for us was less than 6 months and it was pretty much a no-brainer, but we were pioneering composting for the company,” says Martin. “It’s a simple technology and we’ve had no problems or upsets, and we do not have to stop and clean out the drum.” As far as permits, a notification to the state was all that was required since no wastes from other locations are being processed.
He adds that there is no biofilter or other odor control on the composter, and none is required since the closest occupied building is about 200 yards away. “The only time odor is really noticeable is on warm, sultry mornings when the odor hangs around the plant, but it is not an issue. As for leachate, I’d be surprised if we generate 30 gallons/week from the composting drum. We have a Toter at the end of the drain, and whatever leachate we produce is then put onto the compost piles or the vegetable garden.”
Martin estimates that the composting system saves about $250,000/ year in avoided tip fees at the incinerator, and in the ability to grow their own vegetables, trees and ornamental flowers. “We started 6,000 tomato plants last year in our greenhouse and then put them in the garden,” he says. “The on-site garden grows cabbage, broccoli, cauliflower, beans, tomatoes and squash, plus ornamental flowers. We use the vegetables in the meals prepared in our cafeterias. In addition, pumpkins are raised and given to the Toyota Child Development Center at Halloween, and field corn is grown to use in feeders that lure deer away from the main roads on site.”
The greenhouse, manufactured by Growing Space, is used to raise ornamentals that can then be transplanted to flowerbeds. Previously, such flowers were purchased off-site. “The greenhouse completes the waste segregation cycle,” he says. “We’ll use the compost we create from cafeteria waste and other biodegradable materials as a growing medium in the greenhouse. Bedding plants and vegetables will be grown in there year round and eventually be composted again.” An on-site nursery also uses compost to grow thousands of native and ornamental species, including redbud, dogwood and maple trees that are started as saplings, and then grown into transplantable trees for use on site.
As briefly described in a November BioCycle regional roundup, Montclair State University (MSU) in New Jersey has been recycling food waste through a BWO Model 512 since this past summer. Installed next to a trash compactor on the backside of a new $78 million conference center, the composter has replaced four dumpsters that were previously used to dispose of food. “Of course, University administration was concerned about odors from the unit, but so far our experience has been that odor has been less with the composter than the four dumpsters,” says Nicholas Smith-Sebasto, Associate Professor in the University’s Department of Earth and Environmental Science. “We also virtually eliminated the rodent population that was associated with the dumpsters.”
The food service contractor for the conference center is Sodexho. The company’s employees separate the baked goods, coffee grounds, vegetable trimmings, meat and bones that go into the composting drum. According to April Stearns, Catering Director at MSU, the chefs and employees have been able to make the transition to scraping organics into five-gallon buckets, and keeping plastic and other contaminants separate. “We may have 500 people attending an event at the conference center, so we can generate lots of food waste in one day,” she explains. “It’s saving the environment and reducing costs for trash disposal, so it’s a great idea. Sodexho recently held a training program for its chefs at the MSU conference center, so the word is getting out about our program. This project would not have happened without Dr. Smith-Sebasto, and he is in here almost every day weighing how much food we have collected and making sure it is put into the composter.”
Smith-Sebasto also has hosted regional meetings where the compost program was presented to other recyclers and universities. So far, two different bulking agents have been used. First, shredded cardboard, which comes from a Kobra Shredder, was mixed with the food waste, but Smith-Sebasto felt that he did not get sufficient breakdown of the cardboard in the 5-foot diameter by 12-foot long drum. He then switched to sawdust from a local furniture manufacturer, and likes the look of the product. Most of the compost is used for landscaping on the 238-acre campus.
A Model 1040 BWO composter is being used to recycle cotton trash, mixed with slaughterhouse blood, into a bagged compost product. Creating this alchemy is Jerry Kasberg, owner of Birome Gin Co., Inc. in Birome, Texas. “We used to compost our cotton trash in outside windrows but it really needs some nitrogen and moisture to compost,” says Kasberg. “Then, after doing some research, I got our BW Organics composter, and we now get paid a tipping fee to process slaughterhouse blood, and it makes an excellent moisture and nitrogen source for composting the cotton trash.”
Kasberg was able to convert a bagger he uses to bag cattle feed so that it also can bag compost. “I took a waste product from my cotton manufacturing plant, and converted it into a marketable product. I sold 1,500 bags the first year I had it for sale,” he says.
Most days, Kasberg sends a pickup truck pulling a 1,500-gallon tank on a trailer to a slaughterhouse in Waco, Texas, where a load of blood is picked up and pumped into a farm mixer with the cotton trash to get a mixture that is about 60 percent moisture. This is discharged from the mixer onto the infeed conveyor to the rotary drum, where it stays for three days. Upon discharge from the drum, the compost is further stabilized in outdoor windrows. Kasberg runs the drum continually rather than shutting it off for a period each day. “We get temperatures of about 150°F and it really breaks down the cotton trash into a nice product,” he explains.
BERNIE Beers and John Willis have learned a number of valuable lessons over their years of designing rotary drums. For example, BW Organics has been reluctant to build drums larger than 32 cy capacity (50-feet long by 10-feet in diameter) based on their knowledge of the structural problems that seem to plague larger rotary vessels. “Once you get into longer drums you have to have thicker steel shells, more support points and your costs escalate rapidly,” says Willis. “So far we have not had shell cracks, with many of our units running full-time for over 10 years. Our answer to additional capacity is to put additional units in parallel to the first drum, simply extending the infeed and discharge conveyors to go to more than one unit. We also like the redundancy of having more than one drum, so if one is down the other continue to process material.”
The drums have low electrical requirements; most units are chain driven. Instead of support rollers, the drums are cradled at both ends with a plastic liner that offers minimal resistance as the drive chain turns the unit. Because the drums are designed to turn more slowly than the larger drums on the market, more attention is paid to preprocessing the waste. “For applications where we process cow and hog mortalities, we include a shredder and a mixer upfront,” says Beers. “In fact, for all our units we recommend a mixer so that the correct recipe is going into the drum, and then the bugs take over and break down the waste.”
One change being offered is four direct drive motors and gears with four support rollers in place of the chain drive. Acknowledging that large drive chains are difficult to wrestle with if they have to be replaced – which they do on a periodic basis – BWO started offering the direct drive motors as an alternative. Each of the four motors can range from one to six HP, depending on the size of the drum and how fast the customer wants it to turn. “We are building four more units with this new multipoint drive system,” adds Beers. “One unit is for the Toyota Corporation’s project in the Galapagos Islands, one for a dairy in Washington State, one for a turkey processor in upper New York State and one for a prison in Georgia.” The newest BWO model is a one-cy/day “Combo” unit that sells for around $28,000. It is trailer-mounted, and includes a feed hopper and mixer so it can be moved around for demonstrations or to process at different locations.
INTEREST in recycling dairy manure into bedding for cows is increasing The Cornell Waste Management Institute (CWMI) in Ithaca, New York is in the middle of a two year study on the use of dried manure solids (DMS) as dairy bedding. The project started in June 2007 and runs through February 2009. Given that New York dairy farmers spend between $65 and $100/cow annually purchasing bedding material – usually wood shavings/sawdust or sand – there are substantial financial savings from using DMS, defined as the semisolid (approximately 25 percent solids) material derived from a manure stream run through a separator. Dairy farmers report enhanced cow comfort from use of DMS. The CWMI project will document practices on six dairy farms using a variety of methods, including a rotary drum compost unit.
A write-up of the project on the CWMI website site (http://cwmi.css.cornell. edu) provides the following information: “Some farms are using manure solids directly from a separator, others are drying them or using partially composted manure in the barns. Minimizing handling saves time and money but questions remain as to effectiveness in the Northeast climate. In the study, bedding samples are collected and analyzed seasonally though the project period for verification of pathogen levels as documentation of bedding quality.”
John Willis of BW Organics notes the company is seeing more of its clients prepare manure bedding in a drum. “The advantage of putting dairy manure through a rotary vessel is that you can sanitize the manure in just a few days since temperatures easily get up over 131°F, something that is important for control of mastitis infections in lactating cows,” explains Willis. “We are working with a large dairy farm in Texas where the manure is composted in outdoor windrows, and then used as bedding. The farmer continues to have higher somatic cell counts, a measurement of bacterial health, than he would like, so we are working with him to design a manure/water separator that would then feed a rotary composter. It is possible for the manure to go directly out of the drum to bedding, or it could be further processed in windrows, something we are evaluating.”

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