Biofuel production from sugarcane molasses in thermophilic anaerobic structured-bed reactors

This work presents an alternative bioenergy-related management approach for sugarcane molasses through the application of anaerobic digestion (AD) in a two-stage continuous thermophilic (55 degrees C) system to produce biohydrogen (bioH(2)) and methane. The performance of the acidogenic stage (RH2) was assessed by maintaining a continuous and high organic loading rate (OLR; 120 kg COD m(-3) d(-1)), whilst the robustness of the methanogenic stage (RCH4) was investigated based on the increase of the OLR (1.0-25.2 kg COD m(-3) d(-1)). Molecular analyses and an energetic assessment were also conducted, to provide a holistic understanding of the two-stage AD system. Long-term bioH(2) production was achieved at low pH values (similar to 4.0) in RH2 by the co-fermentation of lactate and acetate, and a positive correlation between Clostridium and Leuconostoc genera was identified. Efficient methane production (323-350 NmL CH4 g(-1)COD) was only observed at low OLR (1.0-2.3 kg COD m(-3) d(-1)) in RCH4, although high COD removal levels (>70%) were observed at all operational conditions. Metabolite and molecular analyses indicated inefficient syntrophic and acetoclastic activities (accumulation of acetate, propionate and lactate), indicating that hydrogenotrophic methanogenesis was the prevailing methane-producing pathway in RCH4, specifically by the Methanothermobacter genus. Finally, the energetic potential (8560 kJ kg(-1)COD(applied)) of molasses outperformed the ones of vinasse by at least 25%, indicating that the high availability of biodegradable organic matter in molasses requires a low OLR to offer efficient bioenergy recovery levels.

Automated summary

This study presents an alternative bioenergy management approach for sugarcane molasses through two-stage anaerobic digestion system, showcasing efficient biohydrogen production in the acidogenic stage and effective methane production at low organic loading rates in the methanogenic stage. It was observed that efficient methane production was only achieved at lower OLR, indicating the prevailing hydrogenotrophic methanogenesis pathway in the system.