Bioethanol from agricultural wastes: an Italian lab-scale case study.

Simultaneous microbial hydrolysis of lignocellulosic material and fermentation of resulting sugars to desired products via a single process step is a promising strategy to allow cost-effective production of ethanol. The aims of this project were the isolation, characterization, improvement and possible modification of microrganisms in order to obtain a strain able to both convert cellulose/starch materials from agricultural residues into fermentable sugars and to produce ethanol by fermentation. In this perspective, 170 Saccharomyces cerevisiae strains, known for their fermentation abilities, were screened from our microbial collection and a programme of isolation of new microrganisms from different biological matrices was also started. Few strains of S. cerevisiae, potentially able to utilize cellulose and starch as a sole carbon source, albeit very slowly, were selected. This observation provides the basis for applying natural selection and breeding over an extended period to develop strains of S. cerevisiae with improved ability to use starch and/or cellulose. An alternative and economically interesting strategy consists in pre-treatment of agricultural residues (for example wheat bran) with chemical, physical or enzymatic agents, to get completely or partially degraded cellulose and hemicellulose and simple sugars. These treatments usually do not hydrolyse starch contained in residues. Nevertheless this mixture could be potentially used for ethanol production by the strains of S. cerevisiae previously selected and/or by other strains of Saccharomyces known as able to hydrolyse raw starch contained in the already treated residues. These preliminary results pave the way for the development of one-step bioconversion processing of agricultural wastes in biofuel.