Combined Utilization of Agro-Industrial Wastewaters for Non-lignocellulosic Second-Generation Bioethanol Production

Abstract

Bioethanol is one of the most important renewable fuels, and its production from biomass is a potential substitute for fossil fuels. Second-generation technologies cover a wide range of biomass resources, from agriculture to forestry and waste materials. Although lignocellulosic residues represent an attractive feedstock for ethanol production, their processing is not economical due to problems arising from the recalcitrant nature of the biomass and the need for pretreatment. The main purpose of this work was to evaluate the feasibility of the direct use of three agro-industrial wastes as low-cost feedstock for ethanol production: wastewaters of the sugar-sweetened beverage industry as carbon source, purges of fermentation tanks of the brewery industry as inoculum and corn steep water from the corn starch processing industry as nitrogen source. Fermentations were performed in batch mode under anaerobic conditions, and the concentrations of sugar, biomass and ethanol were monitored over time. The process was optimized using surface-response methodology. Spent brewer’s yeast and corn steep water supplementation at ratios of 12.4 and 8.4% v/v, respectively, were optimal for ethanol production. In these conditions, the sugar available in the soft-drink wastewater was completely depleted in less than 8 h, with an average ethanol yield of 0.45 gethanol/gsugar. The process developed could become an alternative bioprocess for production of non-lignocellulosic bioethanol.