Recycling Composted Organic Wastes on Florida''s Forest Lands
http://edis.ifas.ufl.edu/ ( Publisher's URL )
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Permanent Link: http://ufdc.ufl.edu/IR00001816/00001
 Material Information
Title: Recycling Composted Organic Wastes on Florida''s Forest Lands
Physical Description: Fact Sheet
Creator: Webb, Roger S.
Publisher: University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication: Gainesville, Fla.
Publication Date: 1991
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
Publication Status: Published
General Note: "Published January 1991, Reviewed March 2000."
General Note: "FOR 44"
 Record Information
Source Institution: University of Florida Institutional Repository
Holding Location: University of Florida
Rights Management: All rights reserved by the submitter.
System ID: IR00001816:00001


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FOR44 Recycling Composted Organic Wastes on Florida's Forest Lands 1 Roger S.Webb, Eric J. Jokela, and Wayne H. Smith2 1. This document is FOR 44, one of a series of the Department of Forest Resources and Coservation, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Published January 1991, Reviewed March 2000. Please visit the EDIS Web site at http://edis.ifas.ufl.edu. 2. Roger S.Webb, former Associate Professor, Department of Forest Resources and Conservation; Eric J. Jokela, Professor, Department of Forest Resources and Conservation; and Wayne H. Smith, Director and Professor, Center for Biomass Programs; Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean. The Problem The amount of solid waste generated daily is staggering: approximately 4 pounds per person, enough to cover every square mile of the country, including Alaska and Hawaii, with 270,000 pounds. The daily average for Floridians, 8 pounds per person per day, is twice the national average because the state's 40 million tourists and rapid growth supplement the waste stream. The current annual solid waste total for Florida, 13 million tons, is expected to increase by 38 percent over the next 5 years due to the large daily population increase, about 1000 people per day. Landfill disposal costs in Florida that meet current environmental protection requirements are approximately $50 per ton where sites are available, while incineration costs about $64 to 75 per ton. Composting is much less costly at approximately $30 per ton. In 1988, the Florida Legislature passed the comprehensive Solid Waste Management Act designed to significantly reduce the use of landfills for solid waste disposal while increasing recycling and incineration. While incineration is technically a feasible alternative, the price is great relative to high capital costs for construction, stack clean-up and maintenance, ash disposal and facility management, not to mention a negative public perception of resultant air and water pollution problems. Recycling, especially through composting the degradable organic solid fraction (60 to 70 percent) of the total solid waste stream, is experiencing a renewed interest. Key Reasons for Composting There is renewed public interest in composting for several important reasons: protection of public health conservation of resources safe disposal of wastes reduction of environmental stress attainment of favorable economics development of useful and beneficial products.


Recycling Composted Organic Wastes on Florida's Forest Lands 2 Background When the Industrial Revolution created large urban populations, waste disposal became a serious problem. Even into the early 1900s, the unrestricted open dumping of refuse was standard practice. Since sewage treatment was not widely practiced, the volume of sludge produced was small. Composting of organic wastes during this era related to conserving resources and protecting public health. As citizen awareness of the environmental impact and potential contamination associated with open dumping increased, public opinion in the mid-1900s forced the implementation of more effective and beneficial alternatives to managing municipal wastes. The concept of landfills as a sole means of waste disposal began to change because of rising public pressure, rapid increases in waste generation, and decreasing availability of inexpensive, suitable dumping sites. One alternative to landfilling, incineration, was expensive and undesirable due to the effects of air pollutant emissions upon public and environmental health. Safe waste disposal became a significant impetus for renewed interest in composting. During this period, additional environmental concerns arose from the increased output of wastewater sludges resulting from improved sewage treatment technology. Composting sewage sludge is an economically attractive means of disposal and of resource recovery due to relatively moderate costs involved and the nature of the sludge itself. Through composting, the organic component of sludges as well as valuable plant nutrients are recovered, conserved, and rendered safe to use. What Is Composting? Composting is the biological decomposition of the organic constituents of wastes under controlled conditions. It is the aspect of control that separates composting from natural rotting or decomposition processes which occur in an open dump, sanitary landfill, or unmanaged waste pile. Composting systems are distinguished on the basis of three criteria: oxygen usage (aerobic vs. anaerobic); temperature; and technological approach. Aerobic composting uses aerobic microorganisms which require the presence of oxygen to support the decomposition process. In anaerobic composting, microorganisms accomplish decomposition in the virtual absence of oxygen (air). Typically, aerobic decomposition, in contrast to anaerobic types, is quicker, progresses at higher temperatures, and does not produce foul odors. The main advantage of anaerobic decomposition is that it may be conducted with minimal operator attention and accordingly, the operation may be sealed from the environment. However, most modern composting operations attempt to maintain an aerobic environment. Since composting depends on biological processes to decompose organic components of solid waste, the efficiency and performance of the compost system depends upon maintaining conditions that favor the growth of the inherent microorganism populations. There are five essential factors of the physical, chemical, and biological characteristics of the compost pile: appropriate microbial population(s) sufficient aeration temperature moisture content carbon availability. The types and numbers of microbial populations important in the composting of agricultural residues and wastes, sewage sludge, and the non-toxic organic fraction of municipal solid waste are seldom constraints to the composting process. Those infrequent situations where the microbial population would become a limiting factor would be where: there was a limited variety of microbial species, the wastes had been sterilized before entering the composting process; and the microbes had been exposed to toxic or antibiotic effects due to the chemical nature of the residues.


Recycling Composted Organic Wastes on Florida's Forest Lands 3 Mixing the compost pile at intervals aerates it, but it is often difficult to determine the exact periods to turn the pile. Consequently, aeration is usually conducted in excess, which is not particularly harmful to the composting process, except that an optimum temperature is harder to maintain and excessive evapotranspiration may cause moisture to become a limiting factor. High temperature maintained during the composting process serves 1) to promote efficiency and effectiveness by accelerating the process and 2) to destroy pathogenic microorganisms. High compost pile temperatures, in conjunction with satisfactory levels of the other important composting factors, indicate the likelihood of successful composting. While cool temperatures retard composting, and may even halt the process if the temperature falls too low, a maximum temperature which limits composting has yet to be determined. Moisture content is an important composting factor and may easily become the limiting constraint if not monitored during composting. While dry compost is easier to manipulate and store without causing a nuisance, a moist mixture is necessary to sustain the biological decomposition vital to the composting process. Only after composting has been completed should drying be considered as a necessary prerequisite to storage or sale. Due to the organic portion of sewage sludge and the subsequent composting activities involving this material, the wood chips and sawdust which are mixed with sludge as bulking and moisture absorption agents provide only negligible carbon. Since carbon in wood is made available to degrading bacteria at only a very slow rate, it contributes little to the total carbon fraction. The availability of carbon necessary to feed degradative microorganisms comes almost completely from the organic material to be composted. When Is Compost Safe to Use? Typical temperatures in a well-managed compost pile range from 50 to 65 C, which easily exceeds the thermal death limits of many mesophilic microorganisms pathogenic to animals. Unfortunately, many of the fungal pathogens of plants favor higher temperatures. True tolerance to any temperature must be related to the thermal death-point of the life cycle stage of the particular pathogen of interest. Generally, reproductive stages are more resistant to high thermal death-points than are vegetative states. Additional destruction of pathogenic microorganisms occurs over time due to the physical and chemical changes, e.g., alteration of pH, resulting from the combined activities of microbial populations within the compost system. Also, pathogenic microorganisms exhibit relatively strict nutrient requirements, needing fresh host tissue. Due to competition for this substrate by myriad numbers of competing microorganisms in the compost pile, the pathogens cease growth and either die or alter their physiological activities by forming survival mechanisms such as resting spores. Obviously, a major consideration for using composted organic matter is that it be free of most or all animal and plant pathogenic microorganisms when applied in situations which might perpetuate or encourage spread of diseases. For example, a farmer producing root crops or leafy vegetables to be consumed raw should use only sewage sludge or animal wastes that have been composted for at least one year. If the farmer cannot wait that long, then that compost should be pasteurized before applying to these crops. Also, the requirements for the use of "safe" compost are less vigorous for orchard crops where the main concern becomes microbial contamination of fallen fruit. The requirements for compost safety are further relaxed when the end use is for application on grain or cereal crops, or especially forested areas. Yet, there is a need for some basis of determining compost grade for specific uses, i.e., well-sorted, easily degradable materials like yard wastes versus the myriad potential components in poorly-sorted municipal solid waste. Recycling Organic Wastes in Forests Composting has been demonstrated to be an economically feasible and ecologically compatible method of recycling organic wastes. Where long-term composting is either unnecessary or impractical, applying solid organic waste in forests may be an acceptable means of waste disposal and nutrient recycling. The passage of the Solid Waste Management Act of 1988 encouraged


Recycling Composted Organic Wastes on Florida's Forest Lands 4 environmentally acceptable ways, such as composting and landspreading degradable organic wastes, to reduce, reuse, and recycle wastes that ordinarily would be incinerated or disposed in landfills. A report by the Environmental Protection Agency noted that approximately 70 percent of the solid waste generated daily per person in the United States is appropriate for use in biological decomposition systems. In a study conducted by University of Florida researchers (3), slash pine growth and elemental tissue concentrations were determined for a forest plantation treated previously with municipal garbage composted with sewage sludge. The compost was composed of about 76 percent easily-degradable household organic wastes which were separated from salvageable or non-degradable waste, ground to reduce particle size, wetted with sewage sludge, and aerobically composted. Compost was broadcast and disked into the soil or placed in plowed furrows and immediately bedded. Sixteen years after treatment, tree diameters (dbh) were measured and pine stem and foliage samples were collected for nutrient and heavy metal analyses. Growth results indicated that total pine stem wood biomass (dry weight) experienced a 70 percent increase compared to the untreated control group. Although growth increased with increasing application rates of the composted garbage, differences among the three rates were insignificant. However, the duration of increased slash pine basal area increment growth per tree was directly related to compost application rate; the greater the application rate, the longer the increased growth was observed. Despite the large amounts of garbage compost applied, no significant long-term effects upon elemental tissue concentrations from pine needles and stem tissue were observed. Levels of heavy metals such as cadmium and chromium were insignificantly different compared to standard needle composition data. Accordingly, nitrogen and phosphorus rates were significantly different for treated trees and concentrations of these two important elements increased as garbage compost application rates increased. Since these two elements commonly limit the growth potential of pine on many Florida soils, it is probable that the growth responses observed were due mainly to enhanced availability of these elements in the compost-treated plots. Differences in micro element concentrations were also significantly greater for treated trees but these were not thought to be biologically important. Subsequent soil profile analysis revealed no evidence that nutrients released from the compost moved below the native spodic horizon, except for calcium. From this study of pine growth and the associated soil characteristics, applying garbage compost greatly improved pine productivity without deleterious effects from heavy metals present in the compost. These encouraging results may hopefully expand the use of landspreading composted organic wastes and relieve some of the mounting waste disposal problems created by Florida cities. Increased use of this technique would effectively recycle important nutrients to fertilize forested areas while minimizing any negative impact on site quality. However, further research is required to evaluate the effects of landspreading composted organic wastes upon water quality. Literature Cited 1. Anonymous. 1989. The biocycle guide to composting municipal wastes The JGC Press, Inc., Emmaus, Pa. 195 pp. 2. DeBertoldi, M., M. P. Ferranti, P. L'Hermite, and L. Zucconi. 1986. Compost: production, quality and use. Elsevier Appl. Sci., NY. 853 pp. 3. Jokela, E. J., W. H. Smith, and S. R. Colbert. 1990. Growth and elemental content of slash pine 16 years after treatment with garbage composted with sewage sludge. J. Environ. Qual. 19:146-150.