The rate of composting is believed to depend on a number of rate limiting steps, which include production and release of hydrolytic enzymes needed for the breakdown of substrates; diffusion of solubilized substrate molecules, and oxygen transport and availability within the composting mass (Huang, 1980). Optimisation of the composting process depends on the management of a number of variables such as; (a) nutrient balance; an important component of which is the carbon/ nitrogen balance. A ratio of 25-30:1 is believed to be optimal, in addition to the presence in adequate amounts of all other macro- and micro- nutrients needed by the vast array of micro-organisms that take part in composting (Jimenez and Perez 1991); (b) particle size; the optimum particle size in compost varies with the aeration rate employed, but sizes of 12-5 0mm are considered appropriate for most processes (Biddlestone and Gray, 1985); (c) moisture content; levels of 50-70% are considered optimum (Inaba et al., 1996). Moisture content influences oxygen transfer and attainable temperature in compost (Tiquia et al., 1996; Nakasaki et al., 1985a,b). Airflow rates of 0.6-1.8 m3 air day-1 kg-1 volatile solids are considered adequate. More recently, composting is being considered as a means of developing inocula for the bioremediation of contaminated soils (Laine and Jorgensen, 1996), in addition to its established use for growing edible mushrooms (Miller et al., 1990).
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