As waste managers continue to segment the waste stream, a small but growing volume of materials is being directed towards biomass-to-energy technologies rather than the landfill.
For example, old pallets, furniture manufacturing scraps, green waste and landfill gas (LFG) can all be turned into energy fuel or energy-intensive chemicals.
In the Northeastern United States, biomass represents more than 95 percent of all renewable energy consumed - meeting approximately 5 percent of the region's total energy demand.
In this 11-state region, 28 million tons of wood are burned yearly in residential woodstoves, wood-fired industrial boilers and electric generation plants. Of this amount, one-fifth is comprised of waste wood purchased to fuel industrial and commercial furnaces, boilers and gasifiers.
From an elementary school in Vermont, to a correctional facility in New York and a cogeneration plant in Pennsylvania, wood energy systems use a variety of feedstocks from green wood chips to sawdust and old pallets. These facilities are finding out that having reliable sources of waste wood is more economical than purchasing forest-harvested wood.
The use of wood energy in the industrial sector creates 11,400 jobs and generates $667 million in economic activity annually in the Northeast alone, according to the Northeast Regional Biomass Program, Washington, D.C.
However, many available bio-mass resources have barely been tapped. For example, used pallets, which pose a disposal problem because of their bulk, can represent an energy resource.
In 1990, 460 million pallets were produced in the United States - many used once then discarded. Pallet-derived fuels are increasingly popular compared to urban wood waste sources because pallets have a low moisture content (about 15 percent) and generally are free of paints, stains or other treatments. Most industrial and commercial wood energy plants that would use pallets are direct-fired wood furnaces or wood waste boilers.
Meanwhile, new biomass-to-energy technologies are becoming available. At the McNeil Power Generating Station, Burlington, Vt. - the site of an existing 50-megawatt wood-fired power plant - the U.S. Department of Energy is testing an indirect wood gasifier. By burning wood, the indirect gasifier produces biogas which heats a boiler that provides steam, powering a gas turbine and generating 15 megawatts of electricity.
Another viable biomass energy source is LFG. In Groton, Conn., methane from the town landfill will be used to power a fuel cell. The fuel cell reportedly will produce about 140 kilowatts of electricity - enough to power 100 homes - with no air emissions.
Biomass resources also are used to produce liquid energy fuels such as ethanol, methanol and biodiesel. Used widely as oxygenated additives in gasoline, ethanol (made from corn) and methanol (made from natural gas) both can be manufactured from municipal solid waste or wood.
In Quincy, Mass., Twin Rivers Technologies produces biodiesel fuels from renewable biological sources such as waste products, like restaurant yellow grease..
Petroleum diesel is blended for use in heavy-duty trucks and buses - typically 20 percent bio-diesel and 80 percent petroleum diesel. Using biodiesel reportedly does not require engine modifications to meet federal air quality standards for tailpipe emissions (see diagram).
For more information contact the Northeast Regional Biomass Program, 400 N. Capitol St., N.W., Suite 382, Washington, D.C. 20001. (202) 624-8454.