Production of compost from organic wastes. (1990)

Organic wastes such as livestock manure, sewage sludge, municipal refuse, bark and saw­ dust, should be applied onto cropland as organicfertilizers in order to maintain stable high yields as well as reduce pollution. The composting process under controlled conditions is able to con vert these waste materials into high-quality organic fertilizers. Characterization of the maturing process during composting was studied, to improve the quality of compost and to make clear the degree of maturity. Some chemical indices such as BOD, VFA, CEC, nitrate nitrogen, the ratio of reducing sugar and the C/N ratio, and biological indices such as a germination test, can ex­ press the degree of maturity of the compost. Other properties of composts are also mentioned, such as the content of nutrients, heavy metals and phytotoxic substances. The appropriate appli cation of well-matured compost is recommended as a way of increasing crop growth and soil pro ductivity. INTRODUCTION odors, to kill weed seeds and pathogenic or­ ganisms, and finally, to produce a uniform orThe application of organic fertilizers onto ganic fertilizer suitable for land application. cropland increases soil fertility and productivBiological activity involves the microbio­ ity. Most organic fertilizers are processed logical decomposition of organic matter. from organic wastes such as livestock manure, Many kinds of microorganisms are involved, sewage sluage, municipal refuse, bark and including bacteria, fungi, protozoa, and inverte­ sawdust, crop residues and on. kind brates such as so This nematodes, worms and insects. of conversion of waste materials into useful Populations of all these microorganisms fluctu­ ones is helpful in conserving fertilizer reate, according to whether conditions favo­ are sources, as well as controlling environmental rable or not. pollution. The composting process is the Controlled conditions are important for main method used to produce stable, highcomposting, to distinguish it from other natu­ quality organic fertilizers from organic wastes. ral biological decomposition processes such as This techniqte is becoming more popular, a rotting and putrefaction. Control of the com­ trend likely to continue in the future. In this posting process can shorten the period required paper, principles and methods of composting, for decomposition and stabilization of the or­ and of evaluating the quality of compost from ganic matter, and can produce stable, high­ various organic wastes, particularly animal quality organic fertilizer. wastes, are described, with special reference to the current status of research in Japan. CONDITIONS FOR COMPOSTING PRINCIPLES Composting is a process by which organic wastes are converted into organic fertilizers by means of biological activity under controlled conditions. The objectives in composting are to stabilize the putrescible organic matter in raw wastes, to reduce offensive The carbon-nitrogen ratio (C/N) of waste material is an important factor in successful composting. During composting, microorgan­ isms require carbon as an energy source and nitrogen to maintain and build body cells. A suitable C/N ratio for composting is between 20:1 and 30:1. A higher C/N ratio slows down the composting process, because there