Integrated mild hydrothermal and in situ enzymatic pretreatment improves food waste hydrolysis and net bioenergy recovery

This study prepared compound enzymes using food waste (FW) as the sole substrate, and further integrated mild hydrothermal pretreatment with in situ enzymatic pretreatment to enhance FW hydrolysis and biomethane production. Results showed that the integrated 120 °C hydrothermal and enzymatic pretreatment achieved the best performance in terms of FW dissolution and biodegradability, in which the Δsoluble chemical oxygen demand (ΔSCOD) increased by 99.55%-101.37% and the humification index (HIX) was reduced to 0.198. Peak-differentiation-imitating and two-dimensional correlation spectroscopy (2D-COS) revealed that integrated pretreatment could loosen protein structures, while starch was the most susceptible FW component. These changes led to the enrichment of phylum Chloroflexi and genus Methanosaeta, as well as enhanced synthesis of key hydrolases and upregulation of central metabolic pathways during anaerobic digestion (AD). Ultimately, the highest biomethane yield reached 517.80 mL/g volatile solids (VS), representing an increase of 41.52% compared to the control. Energy balance illustrated that integrated pretreatment could reverse heat deficit into heat surplus, increasing the maximum total net energy recovery (ΔE_total) by 97.38%. Overall, integrated pretreatment strategy provides a sustainable and energy-positive route for FW valorization with strong potential to advance waste-to-bioenergy technologies.