BioCycle June 2010, Vol. 51, No. 6, p. 28
Technology developed for tanneries is being utilized to extract oil from organic waste streams to improve compost process efficiencies and create biofuels revenue streams.
FOR the past 10 years, Bio Waste Solutions Ltd. (BWS) has operated a composting facility at its 4,000-acre farm in Bonby, North Lincolnshire in the United Kingdom (U.K.). The facility originally employed windrows to compost green wastes but switched to in-vessel composting after receiving odor complaints from its neighbors.
Problems with the in-vessel composting system started shortly after the facility began taking in food wastes containing fats, oil and grease (FOG). FOG floating to the tops of the composting containers accumulated into oil slicks. “Bacteria could not operate in the oily product causing problems in achieving the required temperatures and ultimately a poor end product for spreading to land,” explains Lew Dodd, BWS co-owner.
The aerobic process was also considerably slowed by the presence of oil in the raw material, adds Richard Thornhill of Agritec Systems Ltd. (ASL), inventor of the oil extraction technology: “This forced the operators to avoid processing wastes containing oil. Since these waste streams commanded the highest tipping fee this was a considerable financial burden.”
FOG is imminently compostable and actually good in certain proportions but you can have too much of it, says Robert Spencer, an environmental planner specializing in compost facility development and operation. “The problem is the compost gets too wet,” he explains. “With any composting technology you have optimum moisture content.”
FOG can cause operational problems at composting facilities, Spencer adds. “It can be a real mess,” he says, clogging pipes, pumps and screening equipment and getting on conveyors. There also are safety hazards, as FOG can make tipping floors slippery, interfering with equipment operation and causing workers to fall. “There are odor issues too, depending on how rancid the grease is,” he notes.
BWS found a solution to its oil problems at nearby Cranswick Fine Foods, a pork processing facility in Hull, U.K. The composter noticed that the waste from Cranswick did not cause oil problems when processed. Further investigation revealed that Cranswick was using technology developed by ASL to extract oil from its waste before shipping the material to BWS.
ASL partnered with BWS to install a 3 metric tons/hour oil extraction system at the compost operation. For the past two years, the firms have jointly run and profited from the system.
Thornhill originally invented the oil extraction technology to process tannery fleshing (the muscle and fat) removed from cow hides as part of a U.K. effort to eradicate bovine spongiform encephalopathy (BSE) or mad cow disease. Disposal of this material is strictly controlled by U.K. law. “Historically this has been expensive to landfill or incinerate,” he explains. “This was costing tanners money and Agritec developed a process that was satisfactory to the U.K. state vet service.” It also yielded savings to the tanners.
The technology extracts up to 95 percent of the available FOG from organic waste streams such as the source separated organic fraction of municipal solid waste, food processing waste, animal offal and DAF sludge (wash water from meat processing operations containing fats and proteins). The oil extracted is used as biodiesel feedstock, animal feed or renewable oil for power generation.
The amount of oil produced is dependent on the types of waste processed. Food residuals typically yield 6 to 40 percent oil content; food manufacturing wastes, 10 to 50 percent; poultry offal, 26 to 35 percent; and livestock DAF sludge, 5 to 30 percent. Systems range in size from 3 to 15 metric tons/hour and are approximately 10-feet wide, 50-feet long and 12-feet high.
Before processing, the waste is run through a picking line to extract glass and plastics. Metal contaminants are removed by scanning with a metal detector. Remaining materials are fed into the system’s macerator, which reduces the materials to about three-sixteenths of an inch, forming a slurry composed of 10 to 15 percent solids. The slurry is steam-heated in a kettle and cooked in an inline cooker. The process of size reduction and heating, along with some other physical steps, releases the oil from the waste stream. The prepared slurry is then fed into a three-phase horizontal centrifuge, which separates the mixture into oil, wastewater and solids.
“There is no chemical alteration and the technology does not use catalysts,” says Peter Behrle, CEO of Renewable BioSystems, LLC (RBL) in Fairfield, New Jersey, which obtained the exclusive North American license to manufacture and market the system in 2008. RBL is a spinoff of Control & Power Systems.
Incoming waste streams may be mixed to obtain the desired solids content for the slurry. For example, liquid waste from a soup factory is blended with food waste that comes into the BWS facility at 20 to 25 percent solids to produce slurry of 10 to 15 percent solids, explains Martin Zalite, RBL president. The BWS system processes 25 to 40 tons per day of feedstock composed of wastes from pizza, pie and ready meal processing facilities, sludge from wastewater treatment plants and other wastes that the facility is licensed to process.
Wastewater and solids exiting the system are recombined and composted in BWS’s in-vessel composting systems. “It takes five to seven days to compost the material after the de-oiled materials are delivered to them,” Behrle says. “Removing FOG reduced processing time by about two days.”
BWS produces 20,000 metric tons/year of compost that is field applied to its 4,000-acre farm, eliminating the need for commercial fertilizers. “They are getting to the point now where they have too much and are experimenting with a drying and granulating process to be able to bag it,” Zalite says. “The initial thought is to sell it to neighboring farmers.”
BOOSTING REVENUE STREAMS
Up to 40 tons of oil extracted each week is sold to a purveyor of used FOG. The oil is either converted to biodiesel, sold into the animal feed business or sold as direct fire fuel. As of mid-March the oil was selling for about 22 cents/pound, Zalite says.
In addition to speeding processing time and reducing odors, the ASL system at BWS is proving profitable “The tipping fees for the oily residuals are double or triple that for nonoily vegetable type materials.”
The system was easily incorporated into BWS’s operations and requires no additional staffing, Dodds says. “The technology is old technology in a new application so the process works very well.” Removing 10 percent of the feedstock volume prior to composting also increases available capacity for composting.
The smaller 3 tons/hr system consumes about 50-kw of power and 400 lbs/hr of steam, whereas the largest one – 15 tons/hr – requires 250-kw of electricity and 2,500 lbs/hr of steam. Systems cost from $1.5 to $3 million. Payback is estimated between one and two years.
RBL is marketing the system in North America to livestock production facilities, composting operations and anaerobic digestion facilities. Other potential applications include food processing plants, renderers and transfer stations. When the technology is installed at livestock plants, the water is typically put back through the livestock plant’s wastewater treatment system. “The solids can be further processed and turned into protein meal (animal feed),” Behrle explains.
ASL is sending samples of the protein solids exiting an ASL system at the pig slaughterhouse in Germany to an anaerobic digestion facility that processes green waste. “The anaerobic digestion plant reports that the material from the Agritec plant speeds up the digestion process and increases the gas output,” Thornhill says. “Their comment is that it’s like adding a turbocharger to the process.” More details will be available once the testing is completed.
One of RBL’s challenges and strengths is that they are complementary to a variety of processes, explains Priscilla Hayes, program coordinator for the Solid Waste Resource Renewal Group (SWRG) at Rutgers University. “They can improve every process.” But businesses like Trenton Fuel Works, which is trying to build a cellulosic ethanol facility, and Peninsula Compost, which builds and operates composting facilities, must first be successful with their core business before they can make investments into technologies like oil extraction.
For its part SWRG is trying to bring together companies like RBL with investors, municipalities and regulators to encourage “the pieces to come together.” Hayes notes: “We are trying to do whatever it takes. We are trying to connect as many people as we can to move things forward.”
Diane Greer is a Contributing Editor to BioCycle.
June 21, 2010 | General
Oil Extraction Expands Feedstock Processing Options
BioCycle June 2010, Vol. 51, No. 6, p. 28