Resumo

Nowadays, intense research on alternative, renewable energy sources has been triggered by fossil fuels depletion allied to concerns on climate changes and waste management, as well as on the supply of food and energy for a growing world population. Agricultural residues and municipal wastes are potential abundant, cheap and renewable resources for second-generation ethanol production, containing appreciable amounts of cellulose and hemicelluloses that may be depolymerized to sugar monomers by enzymatic hydrolysis. However, the high costs of enzymes and the low efficiency of the enzymatic treatments developed up-to-date, often requiring costly pre-treatment steps, remain as bottlenecks for the development of cost-effective cellulosic ethanol production processes. In this study we investigated the efficiency of mixtures of Trichoderma reesei cellulases and crude extracts from Humicola insolens and Colletotrichum graminicola cultured under solid-state fermentation in low cost media, for the hydrolysis of different waste papers and raw sugarcane trash (RSCT). Colletotrichum graminicola was cultured at 30ºC for 9 days in wheat bran containing 0.9% (w/w) milled corncob and 0.4% (w/w) (NH4)2SO4, with initial moisture of 2.2 mL/g, simultaneously producing 378.1 U/g xylanase, 162.8 U/g ß-glucosidase and 127.3 U/g ß-xylosidase. Humicola insolens was cultured for 4 days at 40ºC in wheat bran, with initial moisture of 1.0 mL/g, producing 15 U/g ß-glucosidase. RSCT at 1% (w/v) final concentration was hydrolyzed in 50 mmol L^-1 acetate buffer, pH 5.0, containing 10 mmol L^-1 sodium azide, at 50°C and 180 rpm. Waste papers were hydrolyzed at the same conditions, but at 45ºC and 140 rpm. A mixture of T. reesei cellulases and C. graminicola crude extract hydrolyzed RSCT with a glucose yield of 33.1% after 48h without any pre-treatment. On the other hand, mixtures of T. reesei cellulases and H. insolens crude extract hydrolyzed untreated magazine paper, towel paper, printed office paper and cardboard with 100% glucose yield after 25h, 25h, 48h and 48h, respectively. The low-cost crude culture extracts from H. insolens and C. graminicola thus show good potential to compose efficient cocktails for the hydrolysis of waste papers and lignocellulosic residues, respectively, and eventually for the development of a practicable cellulosic bioethanol production process.