Microbial biotechnology — Integrated studies on utilization of solid organic wastes

Abstract

The biotechnological exploitation of microbes is becoming more and more important both for industrial purposes and in the treatment and utilization of solid organic waste materials. Agricultural and industrial organic residues contain substantial amounts of cellulose and have the potential of serving as growth substrates for either ruminants or microorganisms. However, due to the intimate association of the cellulose with hemicellulose and lignin, the cellulose is not readily available as a carbon source unless the lignin component of the residues is modified or removed. Mushrooms can transform various solid organic wastes which are inedible by man into a highly valued food protein for direct human consumption. The biological efficiency ranges from 10 to 100%. The solid-state fermentation of lignocellulose-containing agricultural and forest wastes by white rot fungi results in a product which can be used as animal feed. The average rumen digestibility of decomposed wood is between 30 and 60%, as opposed to a maximum of 3% for undecomposed wood. After the mushrooms have been harvested, the spent compost, besides being rich in nitrogenous material, contains partly degraded lignocellulosic components. When this is combined with animal dung or human excreta in a biogas digester, it yields not only biogas but also a good quality soil conditioner. It is suggested that an integrated approach by means of microbial biotechnology for the production of mushrooms, feeding material, biogas and biofertilizer is a feasible approach for rural and urban solid-waste utilization and disposal.