Open mixed cultures for bioethanol production from lignocellulosic materials

This study investigates the feasibility of a new process for the production of bioethanol from lignocellulosic wastes. In the investigated process, conversion of lignocellulosic materials to ethanol is obtained by using microorganisms for all the required process stages, i.e. lignin and cellulose hydrolysis and carbohydrates conversion to ethanol. The aim is therefore to avoid the use of expensive chemical-physical pretreatments for lignin and cellulose hydrolysis, replacing them with cheaper and more environmentally sustainable microbial processes. A key aspect of the investigated process is the use of open mixed microbial cultures, instead of pure cultures of selected microorganisms.

This presentation will discuss the main challenges to be overcome for the development of the investigated process and will present experimental data on glucose and cellulose fermentation by open mixed microbial cultures. Lab-scale bioreactors, inoculated with soil as a source of microorganisms, were operated under anaerobic conditions and fed with either glucose or cellulose (two different particle sizes) as only carbon sources. Ethanol yield up to approx. 20% of the theoretical value was obtained with glucose. In the cellulose-fed reactors, cellulose hydrolysis occurred and it was found to occur faster with the smaller particle size.