Co-digesting sugarcane vinasse and distilled glycerol to enhance bioenergy generation in biofuel-producing plants

Understanding co-digestion technologies from biofuel residues, such as vinasse and glycerol, is an important step in the search for operational improvements in anaerobic systems, enhancing energy recovery through biogas production. This study investigates the methane production from the mesophilic (30 degrees C) co-digestion of sugarcane vinasse and distilled glycerol from a kinetic perspective. Batch assays were conducted to assess the impacts of different proportions of both co-substrates on methane production. The energetic potentials of the biogas from three scenarios, namely vinasse mono-digestion (VM), glycerol mono-digestion (GM), and vinasse and glycerol co-digestion (VGC) were also investigated based on a micro (single sugarcane biorefinery) and macro (entire Brazilian ethanol production) scales. The highest methane yield (352 NmLCH4 g- 1CODrem) was observed in the 1:1 COD-based proportion with 97% of COD removal efficiency. The methane production rate was increased by 39% (169.3 NmLCH4 d-1) and 26% (152.8 NmLCH4 d-1) in reactors fed with 30% and 50% of glycerol, respectively, compared to the mono-digestion of vinasse (121.5 NmLCH4 d-1). On a biorefinery scale approach, the global energetic potential estimated for VGC (32.7 GWh) was 22% higher relative to VM (26.7 GWh) during the harvesting season, whilst extending VGC to the off-season could double VM bioenergy potential. From a global scale perspective, the successful implementation of VGC and GM scenarios in Brazilian sugarcane mills could increase the current bioenergy production from biogas by more than 1500%, meaning an additional electricity supply of 11.7 TWh that could completely replace nuclear power or coal use in Brazil.