AN UNSTRUCTURED MATHEMATICAL-MODEL FOR GROWTH OF PLEUROTUS-OSTREATUS ON LIGNOCELLULOSIC MATERIAL IN SOLID-STATE FERMENTATION SYSTEMS

Inedible plant material, generated in a Controlled Ecological Life Sup port System (CELSS), should be recycled preferably by bioregenerative methods that utilize enzymes or micro-organisms. This material consist s of hemicellulose, cellulose, and lignin with the lignin fraction rep resenting a recalcitrant component that is not readily treated by enzy matic methods. Consequently, the white-rot fungus, Pleurotus ostreatus , is attractive since it effectively degrades lignin and produces edib le mushrooms. This work describes an unstructured model for the growth of P. ostreatus in a solid-state fermentation system using lignocellu losic plant materials from Brassica napus (rapeseed) as a substrate at three different particle sizes. A logistic function model based on ar ea was found to fit the surface growth of the mycelium on the solid su bstrate with respect to time, whereas a model based on diameter, alone , did not fit the data as well. The difference between the two measure s of growth was also evident for mycelial growth in a bioreactor desig ned to facilitate a slow flowrate of air through the 1.5 cm thick mat of lignocellulosic biomass particles. The result is consistent with th e concept of competition of the mycelium for the substrate that surrou nds it, rather than just substrate that is immediately available to si ngle cells. This approach provides a quantitative measure of P. ostren tus growth on lignocellulosic biomass in a solid-state fermentation sy stem. The experimental data show that the best growth is obtained for the largest particles (1 cm) of the lignocellulosic substrate.