Modelling and optimization of simultaneous saccharification and fermentation of agro-food residues

In terms of productivity, bioethanol production from agri-food residues can be improved by carrying out simultaneously the two involved stages (enzyme hydrolysis and alcohol fermentation). This is because the shorter the process duration, the higher the overall productivity achieved. In this work, two kinetic models previously developed by the authors have been combined to obtain a general kinetic model for the simultaneous saccharification and fermentation of lignocellulosic materials. The validity of the combined model has been tested using three different agri-food residues: wheat straw, rice husks and exhausted sugar beet pulp. Later, the model has been used to calculate productivity under many different conditions and to optimize the industrial process. After this study, it is concluded that some important operating variables, such as the enzyme dose and the inoculum strength, must be well coupled to obtain the maximal yield from residues. Thus, the overall productivity obtained in the laboratory experiments was under 5 mg of ethanol per gram of solid waste and per hour, but the simulations in the optimal operating conditions predict productivities of up to twice that.