Prospecção de biomassas lignocelulósicas para co-produção de etanol de segunda geração e biossurfactante empregando processos químicos e enzimáticos

Abstract

Oil depletion, climate change and environmental issues have increased the interest in the use of alternative and renewable sources for the production of energy and products that cause less pollution than petrochemical products. The conversion of biomass into specialty chemicals and fuels has been the focus of industry and researchers over the past decade, so that agro-industrial waste generation can be minimized, environmentally effective technologies developed, and the production of compounds generated from sustainable routes of biofuel increased. In this context, the re-use of lignocellulosic biomass for the production of ethanol and biosurfactants represents a way to reduce environmental pollution and increase the production of compounds generated from sustainable routes. In this doctoral thesis, the production of different crude enzyme complexes (CEC) generated in solid-state fermentation (SSF) using Aspergillus niger was evaluated. The CEC produced was used for the simultaneous production of ethanol and biosurfactant in co-fermentation in the presence of Saccharomyces cerevisiae e Pseudomonas aeruginosa. The CEC that generated higher concentrations of ethanol (8.4 g/L) and biosurfactant (9.1 g/L) was obtained from the extraction using two SSF, fermented medium consisting of steam-exploded sugarcane bagasse and rice bran. This CEC was also used to produce ethanol and biosurfactant in submerged fermentation with steam-exploded sugarcane bagasse and S. cerevisiae e Candida glaebosa; 5.8 g/L of ethanol and 6.6 g/L of biosurfactant were obtained in 48 hours of fermentation. Subsequently, the ability of yeasts S. cerevisiae and C. glaebosa to produce these two substantes in pre-treated rice husk was investigated. With previous studies, it was found that in CEC, the biosurfactant was produced during SSF. Therefore, this production was investigated with the use of A. niger in SSF with different substrates. The highest concentrations of biosurfactant obtained were 7.6 g/L at 72 h of fermentation, with the substrate consisting of exploded sugarcane bagasse and rice bran, and 10.1 g/L at 48 h of fermentation with substrate consisting of wheat bran and rice bran. With this evaluation, the use of these CECs in submerged fermentation with different pre-treated biomasses and the yeasts S. cerevisiae and C. glaebosa for the production of ethanol and biosurfactant was investigated. A study was carried out with levulinic acid (LA) and P. aeruginosa for the production of biosurfactant and it was observed that P. aeruginosa had difficulty in converting the LA in rhamnose. Then, the ethanol production of S. cerevisiae was evaluated with enzymatic hydrolysis and alcoholic fermentation (SHF), varying pH, hydrolysis time and temperature, aiming to increase ethanol production. The best operating conditions studied were 18 h of hydrolysis, at 40 °C and at pH 4.0, generating an ethanol concentration of 19.8 g/L. Using these operating conditions, the CEC was concentrated in a rotary evaporator at temperatures of 50 and 60 °C, and a volume reduction of 25% and 50%. The most favourable condition was the concentration of CEC at 50 °C with a reduction of 50%, and a yield of 21.0 g/L of ethanol. Finally, CEC of three different SSF media and their combinations for ethanol production was evaluated. It was observed that the different combinations of solid media for CEC production influenced the time and concentration of ethanol. The CEC composed of the two solid media of sugarcane bagasse and rice bran was the test that resulted in the highest concentrations of ethanol: 17.6 and 18.5 g/L at 24 and 48 h, respectively.