Environmental Benefits
Many environmental problems of current concern are due to the high production and local accumulations of organic wastes that are too great for the basic degradation processes inherent in nature. Until recent years the utilization of organic wastes and manures in agricultural soils was not problematic because the production was small enough to be used in limited quantities. With adequate appli cation rates, organic wastes are a valuable resource as a soil fertilizer, providing a high content of macro- and micronutrients for crop growth, and they represent a low cost alternative to inorganic fertilizers. Environmental problems arise when the local production and accumulation of manures through intensive strategies is too great, resulting in difficulties in finding sufficient land areas for disposing of the enormous amounts of organic wastes produced. Indiscriminate spreading of large quantities of such organic wastes can damage soil fertility, can cause water pollution and odors, and may present a health risk. The potentially adverse effects of such indiscriminate applications include overfertilization, particularly with N, P, and K; ammonia toxicity for the soil biota; accumulation and concentration of heavy metals in the soil surface and soil biota; gradual increases in soil alkalin ity; salt accumulation in dry conditions; establishment of anaerobiosis and anoxic decomposition pathways; input and dispersal of human pathogens; and ground water pollution.
These important environmental problems can be avoided if organic wastes are treated appropriately before their disposal or use. In this way, aerobic biodegradation can be involved to produce either a high-quality final product or simply to reduce environmental problems through a rapid processing of the waste without increased costs. Through the end of the aerobic degradation process the oxygen demand is low, the organic materials are converted to more stable products, carbon dioxide, and water are released, and heat is evolved. Under field conditions, the degradation process takes place slowly at the soil surface, without reaching high temperatures and mainly under aerobic conditions. This natural process of break down can be accelerated by heaping the material into windrows to avoid heat losses and thus allowing temperature increases (thermophilic composting) or by using specific species of earthworms as agents for turning, fragmentation, and aeration (vermicomposting).
The humified composts and vermicomposts rapidly attain equilibrium with the soil ecosystem without causing some of the major disruptions commonly associated with raw organic wastes. These products are valuable in agriculture as nutrient sources and in soil improvement. Currently, the science of thermophilic composting is well known and applied widely to organic-waste management.
The cultivation of earthworms in organic wastes has been termed vermiculture, and vermicomposting, the managed processing of organic wastes by earthworms to produce vermicompost, has progressed considerably in recent years. Vermicomposting has been shown to be successful for processing sewage sludge, paper industry waste, urban residues, animal waste, horticultural residues from plants, and food industry waste.