Use of hydrothermal pretreatment for enhanced anaerobic digestion of PBAT and PBS: Biogas production and energy balance

Abstract

Biodegradable plastics (BPs) have been identified as a viable feedstock for anaerobic digestion (AD), offering a promising solution to meet the current renewable energy demand. However, certain types of BPs still require pretreatment technologies to enhance their biogas production potential. This study aimed to evaluate the feasibility of hydrothermal pretreatment (HTP) at 150, 175, and 200 °C for either 1 or 3 h in improving the AD performance for treating polybutylene adipate terephthalate (PBAT) and polybutylene succinate (PBS). The pretreatment enhanced solubilization efficiency of both BPs, and in particular, PBS was completely solubilized after HTP at 200 °C for 3 h. The CH₄ yields of PBAT and PBS increased to 550 L CH₄/kg VS and 580 L CH₄/kg VS, respectively. However, HTP of BPs at 200 °C for 3 h resulted in a significant decline in CH₄ yield, likely due to the generation of recalcitrant materials. A strong correlation was observed between solubilization efficiency and CH₄ yield for PBS, whereas PBAT exhibited a lower correlation. In the energy balance analysis (EBA) of the AD process combined with HTP, HTP was a major contributor to energy consumption, and a positive net energy balance (E_net) was obtained under all conditions, except for PBAT treated with HTP at 150 °C for 1 h. The peak energy output (E_output)/energy input (E_input) ratio was 5.9 for PBAT and 6.8 for PBS, indicating that the E_output could sufficiently offset the E_input. Thus, HTP is considered a feasible method for treating PBAT and PBS when integrated with the mesophilic AD process.