Coupling the biochemical and thermochemical biorefinery platforms to enhance energy and product recovery from Agave tequilana bagasse

Abstract The tequila industry is one of the pillar industries in many regions of Mexico, bringing wealth and economic development to rural areas. However, appropriate disposal and management of the tequila manufacturing residues such as the Agave tequilana bagasse (TB) represent not only an environmental challenge but also an economic opportunity. Previous works have unsuccessfully applied biochemical routes for complete TB valorization. Therefore, this study aimed to achieve the full conversion of TB to energy and products by coupling the biochemical and thermochemical biorefinery platforms. The biochemical platform included acid hydrolysis of TB, detoxification of the hydrolysates with activated carbon, and two-stage anaerobic digestion of the undetoxified and detoxified hydrolysates. The energy recovery (expressed as kJ of hydrogen and methane obtained) was optimized by applying a central composite design and using both hydrolysates as substrates. Results showed that hydrogen production with the detoxified hydrolysate outperformed 2 times the undetoxified one; however, the total energy recovery (hydrogen + methane) was not significantly favored with the detoxification process (35.04 and 37.15 kJ for the undetoxified and detoxified hydrolysate respectively), which was attributed to the robustness of the methanogenic process. Regarding the thermochemical platform, the acid hydrolysis of TB accelerated the microwave pyrolysis process and led to a higher oil yields (ca.1.5 times) with similar productions of furfural, phenol and their derivatives but significantly reduced the acetic acid formation compared to untreated TB. During the fluidized bed combustion tests, the Ca-rich TB’s ash mitigated the agglomeration formation and resulted in over 900 min operation with no sign of bed defluidization. This could offer great potentials in co-combustion with other problematic biomass fuels such as wheat straw, which had a defluidization time of 60 min. Overall, these results indicate that coupling the biochemical and thermochemical platforms for Agave tequilana bagasse can be a novel approach to refining gaseous and liquid products and extracting heat energy while disposing the bio-waste from tequila industry.