Enhanced Methane Production and Co-Digestion Characteristics of Various Organic Wastes through Thermal Hydrolysis Pretreatment

This study aimed to enhance methane productivity in the anaerobic digestion of sewage sludge through thermal hydrolysis pretreatment and to evaluate the synergistic effects of co-digestion. Biochemical Methane Potential tests were conducted using six types of organic waste, including sewage sludge, food waste, food waste leachate, livestock manure, and human excreta. The thermal hydrolysis pretreatment was performed at temperatures ranging from 120 to 220℃ for 30 minutes. As a result, the solubilization rate of secondary sludge increased to 23.9–54.8%. In particular, at 140℃ for 30 minutes, the methane yield improved from 104 mL CH<sub>4</sub>/g COD to 159 mL CH<sub>4</sub>/g COD (53% increase), while the COD conversion efficiency increased from 30% to 45.5%. After thermal hydrolysis, the methane yield of secondary sludge reached a maximum of 227mL CH<sub>4</sub>/g COD, representing approximately a 100% increase compared to unpretreated sludge. In the co-digestion experiments, the mixture of thermally pretreated secondary sludge (C site) and food waste leachate at a 7:3 ratio produced the highest methane yield of 261mL CH<sub>4</sub>/g COD, which was about 15% higher than that of mono-digestion. However, in some cases, the synergistic effects were not significant due to substrate dilution and an imbalance in the C/N ratio. These results indicate that thermal hydrolysis pretreatment enhances microbial accessibility by simplifying complex organic compounds in secondary sludge, while co-digestion provides complementary interactions among substrates. The optimal pretreatment condition identified in this study (140℃, 30 minutes) can serve as a basis for process design and energy recovery optimization in wastewater treatment plants and organic waste-to-energy facilities.