| Inedible plant material, generated in a Controlled Ecological Life Support System (CELSS), should be recycled preferably by bioregenerative methods that utilize enzymes or microorganisms. This material consists of hemicellulose, cellulose, and lignin, with the lignin fraction representing a recalcitrant component that is not readily treated by enzymatic methods. Consequently, the white-rot fungus, Pleurotus ostreatus, is attractive since it effectively degrades lignin and produces edible mushrooms. An unstructured model has been developed for the growth of P. ostreatus in a solid-state fermentation system using lignocellulosic plant materials from Brassica napus (rapeseed) as a substrate at three different particle sizes. A logistic function model based on area was found to fit the surface growth of the mycelium on the solid substrate with respect to time, while a model based on diameter, alone, did not fit the data as well. The difference between the two measures of growth was particularly evident for mycelial growth in a bioreactor designed to facilitate a slow flowrate of air through the 1.5 cm thick mat of lignocellulosic biomass particles. The result is consistent with the concept of competition of the mycelium for the substrate that surrounds it, rather than just substrate that is immediately available to single cells. This approach provides a quantitative measure of P. ostreatus growth on lignocellulosic biomass in a solid-state fermentation system. The application of this model, together with an understanding of the metabolism of Pleurotus, led to the development of a novel bioreactor that facilitated perfusion of humidified, oxygen-enriched air through the plant biomass. 87% disappearance of the plant material was achieved after the 60 day fermentation period, upon the onset of mushroom growth. This type of biological subsystem has exciting potential to treat inedible plant materials on a stand alone basis. |
