H. Borazjani, S.V. Diehl, H.S. Stewart and K. Brasher
BioCycle May 2004, Vol. 45, No. 5, p. 42
University projects compost furniture waste with litter, phenolic plywood, swine manure and mortalities, and PCP-treated wood poles.
Disposal of by-products from the two largest industries in Mississippi – forest products and poultry – can pose economic problems for companies and environmental troubles for everyone. According to U.S. Census data, over 890 wood product manufacturers operate in Mississippi covering all aspects of the industry including furniture, paper and sawmills. A survey of 376 wood products manufacturing companies conducted by the Mississippi State University Food and Fiber Center revealed that 12.2 million tons of wood and bark residues were produced in Mississippi per year with less than 75 percent of the residue tonnage utilized for energy or other purposes.
In 1997, the total number of broiler, breeder and pullet farms in the state was 2,250, with broiler farms numbering 1,800. The average number of houses per farms was 4, 2, and 3 for broiler, breeder, and pullet farms, respectively. A typical broiler house will produce 125 to 150 tons of litter material annually generating 225,000 to 270,000 tons of waste for disposal. The normal practice is to apply the litter to pastureland as fertilizer. However, in areas of concentrated poultry production, over fertilization of land can contribute to excess nutrient runoff into the surface and groundwater supplies. Scientists at the Mississippi Forest Products Laboratory have been researching composting wood waste since 1996, beginning by composting furniture wood waste with manure. This research was expanded in 1998 by funding from the USDA Wood Utilization Research grant to study composting of phenolic-bonded softwood plywood, and other forest products related wood waste.
This article presents a brief overview of completed and ongoing composting research at Mississippi State University’s Department of Forest Products on different wood waste sources and poultry litter and also looks at some other Mississippi State University composting research with different source materials.
COMPOSTING FURNITURE WOOD WASTE WITH BREEDER LITTER
Mississippi Forest Products Laboratory and Department of Poultry Science staff conducted a six-month outdoor composting study funded by a Southeast Mississippi Conservation and Development grant. Sawdust from furniture waste was amended with 10 percent and 20 percent poultry breeder litter. Unamended wood waste provided the controls. All treatments and controls were replicated three times. Samples were collected at days 0, 45, 90, and 180. Wood waste sawdust amended with 10 percent and 20 percent showed significant reduction in weight after 90 days. This reduction in weight was over 40 percent for both treatments by day 180. All treatments showed a reduction in toxicity by day 90. Further reduction in toxicity occurred only with wood waste sawdust amended with 20 percent breeder litter. In comparison with day 0, pH levels improved to near 6.5 for all treatments.
Results of this study indicated that composting of furniture manufacturing waste with breeder litter could be an economical, simple, safe and viable option for disposal and utilization of these two major wastes. The composted material was well suited to be used as soil amendment or potting media.
USE OF CHICKEN LITTER TO COMPOST HARDWOOD RESIDUALS
In this study, funded by USDA wood utilization research, chicken manure was added to hardwood sawdust collected from a Mississippi sawmill. The chicken litter was added in 10, 20, and 30 percent increments. Unamended hardwood sawdust provided the controls. Composts were aerated and watered weekly. All percentages of added chicken manure treatments were well composted and showed significant weight loss in 90 days. The compost is currently being evaluated as a commercial potting media for nurseries in South Mississippi.
Hardwood residues are the most unutilized wastes in Mississippi. Large piles of residues at wood processing companies can result in leaching causing a potential environmental hazard for aquatic specimens in streams. A market currently exists for pine bark residues with the nursery industry; however, there is no major current market for unused hardwood bark and sawdust.
COMPOSTING OF PHENOLIC-BONDED PLYWOOD WASTE
In this study, a pilot-scale composting operation was set up at the Mississippi Forest Products Laboratory to test different amendments to plywood sawdust obtained from a furniture company in Mississippi. Eighteen containers were filled with equal amounts of plywood sawdust for this experiment. Sawdust was amended with chicken manure, cow manure, horse manure, cotton gin waste, and inorganic fertilizer solution. Three unamended sawdust filled containers provided the controls. The compost cans were placed outdoors for six months. Treatments were aerated once or twice per week depending on rainfall; moisture content was kept at 60 percent. At the end of 180 days, all treatments showed a decrease in toxicity and weight.
The chicken litter treatment compost was comparable to commercial potting media for growing row crops such as corn, soybean and cotton in a greenhouse evaluation. Total North American production of plywood and oriental strand board (OSB) is expected to grow from 40.3 billion sq ft in 2002 to 45 billion sq ft in 2007. Composting phenolic plywood seems to be a good logical replacement for landfilling.
COMPOSTING AND HOG FARMS
Wayne Frank, former Assistant Professor in waste management with MSU’s Animal and Dairy Sciences department, led a team that developed an alternative waste disposal system that keeps swine odor levels down and provides a value-added product for additional on-farm revenue. The three-year research project was funded in part by the Mississippi Farm Bureau Federation.
In traditional systems, swine waste is collected into lagoons and diluted with water. The effluent is then applied to surrounding pastures as a fertilizer. The ban on new construction of waste lagoons meant a new method of management and disposal was needed.
The team’s answer to that need is a modified deep-litter system, which consists of a two-inch layer of sawdust maintained on solid, sloped concrete pen floors. As the pigs move around the pens, sawdust is mixed in with animal waste which moves down the slope and is collected in a pit. The litter is then composted for row crop and horticulture production.
Since the moratorium on new hog production facilities, another obstacle has fallen into the path of all livestock producers. “About the only other approved method to dispose of animal mortalities is in a landfill,” Frank says, “and that is a short-term solution, which is expensive to the producer. Plus, the mortalities have to be transported off-farm to the landfills.”
Researchers found composting to be the answer to this challenge as well – leading to inexpensive but efficient methods of on-farm composting and opportunities for additional on-farm revenue. In-vessel composting with some method of rotation is the best method for Mississippi’s humid climate. Options are as simple as building a homemade composter from steel road culverts placed on house trailer axles or purchasing used asphalt- or cement-mixing trucks. Commercial composting containers are more expensive and can handle up to 50 tons of compost per day.
“Composting reduces the volume of waste by 50 percent, and it reduces odors as the finished product has a more pleasant earthy smell,” Frank sums up. “It also kills all known pathogens and stabilizes nutrients, which means there are no runoff concerns. Nutrient runoff from composted materials would typically only occur when there is so much water that the compost floats away with the flow.”
MICROBIAL DECOMPOSITION OF PENTACHLOROPHENOL TREATED WOOD
Of the 36 million pentachlorophenol (PCP) treated utility poles estimated to be in service, about 1.5 million are removed annually. Disposal of these poles has created a substantial burden on utility companies. PCP-treated wood is not currently considered a hazardous waste in most states and can be discarded in landfills. However, decreasing landfill space and possible decrease in the disposal limit for PCP-treated wood (based on the Toxic Characteristic Learning Procedure) suggest a need for alternative disposal methods.
Research at Mississippi Forest Products Laboratory examined soil to enhance the microbial depletion of two different PCP concentrations in wood flakes from a treated utility pole. Treatments in the first study consisted of wood flakes containing 1,540 g/g PCP mixed with, and without, soil or microorganisms. By the end of the study, the PCP concentration was reduced by approximately 40 percent in treatments containing wood or wood plus bacterium and reduced by 68 percent in wood inoculated with fungus. PCP reduction was 40 percent, 88 percent, and 95 percent in treatments containing wood plus autoclaved soil and wood plus autoclaved soil plus a bacterium or fungus respectively. In nonautoclaved soil treatments, PCP concentration was reduced by 88 percent or greater with or without added bacterium or fungus. The addition of nonautoclaved soil significantly enhanced the degradation of PCP compared to autoclaved soil. Degradation was initially faster in fungal than bacterial inoculated soil treatments but was equal at the end of the study. The reduction in PCP concentration also corresponded to a reduction in toxicity. Treatments for the second study consisted of PCP treated wood flakes (15,000 g/g), wood flakes plus nonautoclaved soil, and wood flakes plus nonautoclaved soil plus added bacterium or fungus. The PCP concentration in the wood flakes was reduced by 32 percent in treatments containing soil plus bacterium and 45 percent in treatments containing soil plus fungus. Results from both studies indicated that nonautoclaved soil addition significantly enhanced microbial degradation of PCP in wood.
Hamid Borazjani is a professor in the Department of Forest Products at Mississippi State University. His research interests include bioremediation of organic chemical wastes in soil, water, wood, and sludges. Susan Diehl is an associate professor in the Department of Forest Products. Her research interests include bioremediation of soil and water contaminated with organic wood preservatives. Harold Stewart is a former assistant research professor at Mississippi State University. His research primarily deals with tool wear and wood machining. Karen Brasher is publications editor and web designer for the College of Forest Resources and the Forest and Wildlife Research Center at Mississippi State University.