Effect of hydrothermal pretreatment on the biogas production performance of co-digestion of <i>Chlorella</i> and sludge

To address growing energy demand and promote environmental sustainability, the development of diverse biomass-based renewable energy is crucial. Co-digestion of <i>Chlorella</i> and sludge has been recognized as an effective strategy to improve methane production efficiency from biomass. This study aimed to explore the optimal ratio of <i>Chlorella</i> and sludge. On this basis, hydrothermal pretreatment was applied to the <i>Chlorella</i>-sludge mixture to investigate the temperature effects on co-digestion performance. This step aimed to optimize methane yield and identify the most suitable pretreatment temperature. The anaerobic digestion kinetics were evaluated by fitting experimental data to both the Fitzhugh first-order kinetic model and the Modified Gompertz model. Additionally, metagenome sequencing was performed on samples before and after hydrothermal pretreatment to elucidate the impact of pretreatment on microbial community dynamics during the acidogenesis phase of anaerobic digestion. The experimental results demonstrated that a 20-day co-digestion period with a VS <i>Chlorella</i> to VS sludge ratio of 2:1 yielded the highest biogas production, reaching 250.98 mL/g VS. After 30 min of hydrothermal pretreatment at 180 °C, the co-digestion efficiency of <i>Chlorella</i> and sludge reached the optimal level, with a cumulative methane production of 261.02 mL/g VS, which had a significant impact on microbial diversity.