Hydrothermal Pretreatment of Agave Bagasse for Biomethane Production: Operating Conditions and Energy Balance

In this study, agave bagasse (a lignocellulosic residue) was pretreated by steam explosion to increase the solubility of carbohydrates in the hydrolysates. The operational variables studied were pressure (0.28, 0.47, and 0.67 MPa, corresponding to 116, 142, and 154 degrees C, respectively) and pretreatment time (5, 10, 15, and 20 min). The conditions that favored the highest solubilization of glucose (66 + 4 mg L-1), arabinose (160.31 + 3.2 mg L-1), and the chemical oxygen demand (COD, 4395.71 + 22.44 mg L-1) were 154 degrees C and 10-min. On the other hand, the maximum solubilization of total carbohydrates (TC, 2177.99 + 197.22 mg L-1) and xylose (43 + 2.8 mg L-1) was obtained at 154 degrees C and 15-min. Pretreatments catalyzed with H2SO4 at 154 degrees C and 10-min resulted in 3, 2.7, and 100-times TC, glucose and xylose concentrations, respectively, as compared to the uncatalyzed pretreatment. However, concentrations of potential inhibitor compounds (i.e., acetic acid, furfural, and hydroxymethylfurfural) increased as well, 26, 120 and 18-times, respectively. A biochemical methane potential (BMP) test of the hydrolysates resulting from the 154 degrees C-10 min conditions was used to calculate the energy balance of their conversion to methane. When considering only the energy invested in the pretreatment, the process showed an efficiency of 247%, thus being energetically feasible. The integration of methane production to the tequila processes could be implemented using the steam flow already present in the process, improving energy efficiency and reducing the environmental impact of this industry.