Effect of thermophilic and hyperthermophilic hydrolysis on mesophilic anaerobic digestion of food waste

Food waste (FW) has a high content of water and is easily biodegradable; thus its treatment through anaerobic digestion (AD) is an attractive method. Even though theoretically thermophilic AD is preferred over mesophilic AD due to higher rate of organic solids destruction and biomethanation, as well as higher reduction of pathogens, most anaerobic digesters are operated under mesophilic conditions as the operational parameters such as cost, process stability, and structural requirements are simpler. In order to reach the advantages of both mesophilic and thermophilic AD processes, thermophilic/hyperthermophilic hydrolysis can be performed prior to mesophilic biomethanation in the same digester. Therefore, this research aims at investigating the effect of thermophilic/hyperthermophilic pretreatment on mesophilic biomethanation of FW through batch experiments. Synthetic FW was pretreated at thermophilic (500C, 600C) and hyperthermophilic (700C, 800C) temperatures for 12, 24, 36, 48 hours, and then placed at mesophilic (32-340C) conditions. Thermophilic pretreatment enhanced the mesophilic biomethanation of FW, whereas hyperthermophilic (700C and 800C) pretreatment did not result in an enhanced biomethane production. Specific biomethane production of untreated FW amounted to 433.6±4.3 ml/gVS, whereas the highest biomethane yield of 627.2±7.1 ml/gVS was achieved when applying a pretreatment at 500C for 12h prior to the mesophilic digestion.