BIOFUEL ETHANOL PRODUCTION BY MICROBIAL FERMENTATION OF RICE STRAW WASTES

Abstract

The present work aimed to study the ability of some microorganisms to produce bioethanol as economical and clean renewable energy source by using a microbial fermentation of rice straw wastes. For this purpose twenty four isolates of cellulolytic fungi were isolated from different sources mature and underdone compost and rice straw. These fungal cultures were tested for their ability to produce cellulytic enzymes using different media. The most efficient isolates were tested for cellulase activity of and their efficiency to produce fermentable sugars by saccharification of rice straw wastes, using several pretreatments. The factors affecting the reducing sugar productivity and production of bioethanol by Saccharomyces cerevisiae under static condition were also observed twenty four cellulolytic fungal of culture were isolated from different sources. The isolates were identified according to there morphological and taxonomic characteristics. The highest fungal cultures belonged to genus Aspergillus (17) isolates followed by Trichoderma (5) isolates and finally the genus Rhizopus (3) isolates. The maximum reducing sugars obtained by Aspergillus flavus (2103) at 2nd day of fermentation followed by Trichoderma viride c34 at 4th day of fermentation by using rice straw pre-treated by grinding together with 1% sulfuric acid as a carbon source were 1.863 and 1.230 (g/l) respectively. The highest decomposition rate of pre-treated rice straw by grinding together with 1% sulfuric acid was achieved by Aspergillus niger (2107) being 66.7% while the lowest value was achieved by Trichoderma viride c34 being 57.3 % while Aspergillus flavus (2103) gave the highest productivity of fermentable sugars being 62 % of rice straw. The efficiency of culturing methods revealed that the solid state process showed higher quantity of total sugars as compared to shake culture process. The optimum pH, temperature and inoculum size for producing the highest fermentable sugars were 5.0-5.5, 25-30° C and 4-5% respectively.

Key words: Rice straw, Bioethanol, Microbial fermentation, Celluilolytic fungi, Pretreatment of rice straw, Tricoderma viride, Aspergillus, Saccharomyces cerevisiae.