ENZYMATIC-HYDROLYSIS OF PRETREATED RICE STRAW

California rice straw is being evaluated as a feedstock for production of power and fuel. This paper examines the initial steps in the proce ss: pretreatment of rice straw and enzymatic hydrolysis of the polysac charides in the pretreated material to soluble sugars. Rice straw was subjected to three distinct pretreatment procedures: acid-catalyzed st eam explosion (Swan Biomass Company), acid hydrolysis (U.S. DOE Nation al Renewable Energy Laboratory), and ammonia fiber explosion or AFEX ( Texas A & M University). Standard conditions for each pretreatment wer e used but none was optimized for rice straw specifically. Six commerc ial cellulases, products of Genencor International (USA), Novo (Denmar k), Iogen (Canada) and Fermtech (Russia) were used for hydrolysis. The Swan- and the acid-pretreatments effectively removed hemicellulose fr om rice straw, providing high yields of fermentable sugars. The AFEX-p retreatment was distinctly different from other pretreatments in that it did not significantly solubilize hemicellulose. All three pretreatm ent procedures substantially increased enzymatic digestibility of rice straw. Three commercial Trichoderma-reesei-derived enzyme preparation s: Cellulase IOOL (Iogen), Spezyme CP (Genencor), and Al (Fermtech), w ere more active on pretreated rice straw compared than others tested. Conditions for hydrolysis of rice straw using Cellulase IOOL were eval uated. The supplementation of this enzyme preparation with cellobiase (Novozyme 188) significantly improved the parameters of hydrolysis for the Swan- and the acid-pretreated materials, but did not affect the h ydrolysis of the AFEX-pretreated rice straw. The three pretreatment te chniques were compared on a basis of a total yield and distribution of fermentable carbohydrates released by enzymatic hydrolysis (the highe st possible substrate concentrations were used, 150 g/l for the Swan- and the acid- and 100 g/l for the AFEX-pretreated straw enzyme loading of 6.7 filter paper units (FPU) and 6.7 cellobiase units (CBU) per gr am of dry straw was the same for all pretreated materials). A combined yield of monosaccharides produced by a pretreatment step and by enzym atic hydrolysis was found to be 46, 42 and 37 g/l for the Swan-, the a cid- and the AFEX-pretreated rice straw, respectively. (C) Elsevier Sc ience Ltd.