Flower City Mushrooms LLC (FCM) has conducted a pilot scale project to examine the technical and economic feasibility of using spend sawdust, wheat straw and corncob organic mushroom substrates to produce fuel ethanol.
Two strategies were employed to evaluate changes in fiber content and water soluble carbohydrate concentrations as a precursor to ethanol in a fermentation process. The first strategy was to analyze the samples to compare fiber content and water soluble carbohydrates before inoculation, after mycelial growth and after fruiting. The second strategy involved microscopic inspection of the substrate at various stages for evidence of lignin destruction and weighing of dried substrate solids before and after enzymatic hydrolysis to determine the percentage of solids that were hydrolyzed.
The results of this research reveal that the mycelial growth of white rot fungi did in fact degrade the lignin by approximately 50% in the case of Lentinula edodes on hardwood sawdust substrate and by approximately 25% in the case of Pleurotus sjaor caju on wheat straw. Concurrent with lignin reduction, fiber content was reduced by an average of 28% on the sawdust substrate and by 41% on the wheat straw substrate and simple sugar concentrations increased by 500% on the straw substrate and 400% on the wheat straw substrate. Enzymatic hydrolysis of these substrates using the Genecor Cellulose Enzyme CP further increased simple sugar content by approximately 150%. The results of this work indicate that conversion of 10,000 pounds of spent mushroom substrate would produce only 51 gallons of fuel ethanol using the shiitake/sawdust substrate formulation and only 82 gallons of fuel ethanol using the oyster/wheat straw substrate formulation, in both cases making it an economically infeasible pursuit.