Optimization of Combined Alkaline-Hydrothermal Pretreatment for Enhancing Bio-methane Production from Paulownia fortunei Wood Using Response Surface Methodology

Abstract

Paulownia wood is recognized as a promising source of lignocellulosic resources as feedstock for biofuel production processes. However, the inherent resistance of lignocellulosic materials to biological degradation poses a significant challenge in the anaerobic digestion (AD) process. This study aimed to assess the impact of combined alkaline-hydrothermal (CAH) pretreatment with sodium hydroxide on enhancing bio-methane yield (BMY) from fast-growing Paulownia fortunei wood. The effect of pretreatment on morphological characteristics and biomass compounds was examined using FESEM, EDX, and XRD techniques. The process was analyzed and optimized using the RSM-CCD methodology. The investigated parameters included NaOH concentration (3, 6, and 9% w/w), pretreatment temperature (60, 120, and 180 °C), and time (30, 75, and 120 min.). The analysis of variance (ANOVA) results showed that all selected parameters had a significant effect on the BMY. Moreover, the optimal pretreatment conditions were a NaOH concentration of 7.91% w/w, a temperature of 170.9 °C, and a time of 86.6 min., leading to a BMY of 300.2 mL/g.VS. The EDX analysis revealed that carbon content in the CAH pretreated samples decreased by 9.98%, while oxygen content increased by 17.9%. Furthermore, the FESEM results revealed that the surface of untreated Paulownia wood is highly compact and inaccessible, whereas the open and disintegrated structure of the CAH pretreated sample could be responsible for the improvement of bio-methane yield.

Graphical Abstract