Brewer's Spent Grain as a Valuable Substrate for Low Cost Production of Fungal Cellulases by Statistical Modeling in Solid State Fermentation and Generation of Cellulosic Ethanol

Abstract

Brewer's spent grain (BSG), a brewery waste was used as a substrate for cellulase production employing a laboratory isolate of Aspergillus sp. SS-25 under solid state fermentation as well as for cellulosic ethanol production. The cultural parameters and media components were statistically optimized for enhancing the cellulase yields employing Plackett-Burman design model. A near-optimum medium formulation for maximum cellulase production by the fungus was determined that increased the CMCase, FPase and β-glucosidase yields by 3.1, 3.6 and 2.1 folds, respectively. Predicted results showed that supplementing malt spent grain with 20% (w/w) wheat bran, 2% each of potato peels, peptone, soyabean meal, tryptone, malt extract, 0.14% NH4SO4 0.002% CoCl2, 0.0006% FeSO4 0.1% MnCl2, 0.1% NaNO3, 0.03% urea, 0.03% NH4Cl, maintaining 70% moisture content and incubation at 30°C for 6 days induced maximum production of all the components of cellulase system yielding 295, 90 and 80 IU/g respectively for CMCase, FPase and β-glucosidase against the predicted yields of 289, 94 and 82 IU/g dry solids. The enzyme preparation worked well in degrading the cellulose fraction in steam pretreated BSG into glucose revealing 75% cellulose conversion efficiency by way of yielding 134 mg glucose/g of BSG. The fermentation efficiency of glucose was found to be 91% producing 78μl ethanol/g of BSG.