Integrated production of ethanol and biogas from sugarcane bagasse: obtaining biogas from pretreatment liquor and vinasse

Abstract

The search for alternative biofuels to fossil-based fuels is essential for the transition of society towards a sustainable bioeconomy. Among the possibilities, bioethanol and biogas can be highlighted, particularly in countries like Brazil, where there is an abundance of raw materials for their production. Second-generation ethanol has been the focus of numerous studies over the past decades, with its feasibility being linked to production in biorefineries using fermentable sugars present in lignocellulosic biomass. For the economic viability of the biorefinery, however, aspects such as the generation of multiple products from the material streams produced in the process must be considered. After the pretreatment and enzymatic hydrolysis stages, for example, streams containing lignin are generated, along with vinasse obtained from alcohol distillation. Lignin, due to its high calorific value, can be used for energy generation in boilers, while vinasse is commonly used for fertigation of sugarcane. Alternatives for the use of these streams could result in greater profitability of the process, enhancing its economic viability. In recent years, studies have been carried out at the Laboratory of Biopolymers, Bioreactors, and Process Simulation (LBBSIM) at the School of Engineering of Lorena - University of São Paulo (EEL-USP) aiming to evaluate biomass pretreatments assisted by hydrodynamic cavitation, which offer advantages such as achieving high efficiencies under mild temperature and pressure conditions. These pretreatments typically result in liquors rich in lignin degradation products, which, however, are of low concentration and low molecular weight, preventing their precipitation in acidic media, thus limiting their use for energy generation. Therefore, this project proposes the evaluation of biogas production from the organic compounds present in the liquor obtained from the pretreatment of sugarcane bagasse by a process assisted by hydrodynamic cavitation, mixed in different proportions with vinasse. Initially, the liquor will be obtained under conditions previously defined by the research group, and it will be characterized in terms of its composition, particularly regarding BOD, COD, volatile solids (VS), and C/N ratio. Then, the liquors will be studied to determine their potential for biomethane production, with the biogas production experiments being conducted considering the organic load (BOD/COD/VS) and taking into account the co-digestion of the liquor with vinasse. It is expected that, through the execution of this project, a contribution will be made to the improvement of lignocellulosic biorefineries, with the development of national technology for biofuel production. (AU)