Thermophilic anaerobic biodigestion of vinasse in combined acidogenic-methanogenic systems to enhance bioenergy recovery in first generation sugarcane biorefineries

Abstract

The difficulties associated to the trade and use of fossil fuels in the recent decades resulted in the development of alternative energy sources, considering an ever-increasing demand for energy, especially in the automotive sector. Among the alternative sources, we highlight the industry of biofuels, especially the one related to the production of ethanol. Ethanol production is based on the fermentation of sugars found in biological materials (eg sugarcane, corn, etc.) and on the distillation of the alcoholic media formed during the fermentative process. Stillage is characterized as the main wastewater resulting from this process, with high concentrations of organic matter as well as acidic and corrosive characteristics. Currently almost the entire volume of stillage generated in Brazilian distilleries is directed to the fertigation of sugarcane, due to its fertilizer character. However, the polluting potential of stillage characterizes its disposal in the ground as problematic, considering probable negative impacts over the soil and water resources in case of excessive dosages. Considering the available treatment technologies, we highlight anaerobic digestion, a process that associates the reduction in the polluting potential of effluents to the generation of energy through biogas. Thus, in this work we intend to study aspects of the environmental adequacy and energetic reuse of stillage, considering the application of anaerobic digestion. The main objective of this research includes analysing the feasibility of the possible technological routes for the energy reuse of biogas, based on the processes related to the enrichment of syngas in a biorefinery. We intend to assess the stability and the production (yield) of hydrogen and methane in anaerobic reactors in series, respectively acidogenic (packed fixed bed) and methanogenic (packed and orderly fixed bed), applied to the treatment of stillage, operated in bench scale. The experimental results will be subsequently included in the flowchart of the biorefinery, so we can analyze the best scenario for the reuse of biogas (methane and hydrogen or methane only). Furthermore, we will evaluate the microbial diversity in the anaerobic reactors and the energetic potential, ie the energy recovery capacity of the biogas generated in the reactors. In the last step we will compare the energetic potential of stillage to the energy consumption associated to the production of ethanol.