Decomposed biosolids (e.g., leaves, crop residue, animal waste) have long been used to recycle plant nutrients and enhance soil fertility. It is one of the
Barry Commoner speaks to protesters outside a hotel in New Jersey where Exxon stockholders met in 1989. (Corbis-Bettmann. Reproduced by permission.)
humus rich soil component derived from plant breakdown and bacterial action most ancient of agricultural innovations, as is evidenced by an ancient Telgu proverb "Leaf manure produces luxuriant growth" (Donahue et al., p. 154). Despite its long history, the scientific principles and systematic explanation of the techniques involved were not described until 1935 when Sir Albert Howard, working in Indore, Madya Pradesh, India, described the so-called Indore method of composting in which plant and animal waste is converted into humus. The process was developed between 1924 and 1931 for two reasons: to eradicate parasites from biosolids and maintain soil fertility. It was realized that "improved varieties by themselves could be relied upon to give an increased yield in the neighborhood of 10 percent, improved varieties plus better soil conditions were found to produce an increment up to 100 percent, or even more" (Howard, p. 39). The process involves creating an admixture of animal and plant wastes with a base for neutralizing acidity, and managing the admixture so that microbial processes are most effective at humifying the biosolids. The fermenting processes are allowed to occur in a shallow pit to avoid loss of water. The pit is surrounded by a cutoff drain to prevent run on and by a thatch of roof to keep rains out and reduce the risk of inundation.
Thus, composting is the biological reduction of biosolids into a soil-like, nutrient-rich material. The composted product is safe and easy to handle, and does not induce nitrogen deficiency in recipient plants by nitrogen stabilization in the compost. It suppresses disease infestation by partial sterilization and detoxifies pollutants. Principal types of organic wastes used in composting are animal manure, yard waste, municipal solid waste, paper mill sludge, municipal sewage, and fermentation waste. An important precaution when creating a usable end product is to exclude those materials that contain weed seed or cuttings which may sprout and become weed, or infested material that may spread pathogens to recipient crops. These organic materials are decomposed into humus outside of the soil by a process called humifica-tion that normally occurs within the soil. The application of biosolids directly to soil may have adverse impacts on soil quality and plant growth. With decomposition of biosolids and their humification the compost pit minimizes the adverse impacts. Techniques have also been developed for making satisfactory compost from sewage sludge. Of concern here is the risk that heavy metals in municipal sludge will contaminate cropland.
Composting is a hygienic way of recycling nutrients in the organic byproducts of agriculture, urban, and industrial activities. It represents safe storage and easy handling, and is an economic source of plant nutrients. It is an important strategy for handling a significant volume of by-products. The quantity of biosolids available for composting in the United States is large (see table). Properly used, it is a major resource for enhancing soil quality and improving environments. Compost material is principally used for the reclamation of drastically disturbed (e.g., mined) soil and other degraded ecosystems, and for landscaping and agriculture. Rather than cause environmental pollution, properly composted organic material can be a major asset in the enhancement of soil fertility, restoration of degraded soils, and sequestration of carbon. Carbon sequestration implies removal of carbon dioxide from the atmosphere either biotically through photosynthesis as plant products or abi-otically by capturing from industrial sources. Subsequent storage of the carbon thus captured into long-lived pools such as soil, forestry products, geological strata, or ocean.
COMPOSTING PROCESS MATERIALS FLOW DIAGRAM
COMPOSTING PROCESS MATERIALS FLOW DIAGRAM
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