Wood wastes can be a lucrative commodity depending on local market conditions and available technology.
Relatively easy to recycle, wood wastes have many uses that make them valuable. In addition, technology for wood waste recovery and reuse is now commercially available, proven in use and relatively simple, according to Philip C. Badger, manager of the Department of Energy's Southeastern Regional Biomass Energy Program (SEBEP) at the Tennessee Valley Authority Environmental Research Center, Muscle Shoals, Ala.
Except for a small amount containing chemical preservatives, urban wood wastes (tree trimmings, brush, land-clearing debris, leaves and used pallets) are relatively benign. Typically, the wastes arrive at the landfill already sorted in monoloads, making recovery easier. If sorting is necessary, however, higher quality materials should be removed from the waste stream first to ensure the cleanest materials.
Potential wood waste markets include feedstock for wood composite materials, paper pulp, fuel for energy generation, animal bedding and litter, mulch, soil amendment or compost, landfill cover and road stabilization. Because of their bulk, the wastes cannot be cost-effectively transported long distances.
If it is used as an energy source, wood waste may be processed into briquettes, charcoal or pellets, as well as liquid or gaseous fuels. The value for fuel usage depends on the waste's energy content, cleanliness, particle size and transportation costs (see chart).
Energy content depends on moisture levels. For example, bone-dry, clean hardwood has approximately 8,500 BTUs per pound of energy, while freshly cut wood will produce only about 4,000 BTUs per pound.
Pallets and wooden packing materials stored indoors have an energy value of 7,500 BTUs per pound. Fortunately, wood dries rapidly with proper ventilation; dry wood, however, can spontaneously combust.
Dirt and other non-wood materials will decrease fuel value by increasing the waste wood's ash content, reducing combustion efficiency and contributing to equipment and slagging problems.
A sizable federal tax credit is available for producing and using gas from biomass like wood wastes. Non-financial benefits include reduced landfilling.
Since biomass fuels are formerly growing plants, carbon dioxide emissions are recycled and do not contribute to any net global climate change. With the exception of particulates, wood fuels produce far less emissions than other fossil fuels. Compared to coal, wood has approximately 70 to 90 percent less ash and can be used in agriculture or to stabilize sewage sludge for land application.
Two Alabama cities, Anniston and Decatur, have very successful programs for recycling woody materials. Anniston's wood waste processing center is operated by Miller Sand and Gravel as a public/private venture. It accepts all wood and yard trimmings delivered by individuals and businesses and also those collected by the city.
Primary products are green wood chips, mixed green/processed chips and compost made from leaves, yard trimmings and older wood chips. Products are sold to individuals, landscaping companies and for use in city parks and golf courses.
As an incentive, a $12.50 tipping fee is charged - versus the $22 fee at the landfill. Here, recycling has become market-driven rather than mandatory. To date, the project reportedly has produced more than $50,000 in revenue as well as avoiding more than $120,000 in col-lection and landfill costs.
In a program started in 1992, Decatur now collects about 14,000 tons of yard trimmings, glass clippings, stumps and pallets annually from the city's 18,000 house-holds and businesses. Chipped wood from pallets and large wood pieces are used as boiler fuel by Champion International Corp., Cortland, Ala.
Trimmings and grass clippings are processed into a mulch used by a local soil producer and by residents as compost material. Likewise, processed leaves vacuumed up in the fall are sold to another soil producer.
Since 1992, the program has recycled more than 45,000 tons of green and woody materials - 40 percent from residential collection - into $90,000 in revenues.