Evaluating Methane Production from Anaerobic Mono- and Co-digestion of Kitchen Waste, Corn Stover, and Chicken Manure

Anaerobic mono- and co-digestion of kitchen waste (KW), corn stover (CS), and chicken manure (CM) under mesophilic (37 degrees C) conditions were conducted in batch mode with the aim of investigating the biomethane potential (BMP), biodegradability, methane production performance, and stability of the process. An initial volatile solid concentration of 3 g VS L-1 with a substrate-to-inoculum (S/I) ratio of 0.5 was first tested, and two S/I ratios of 1.5 and 3.0 were evaluated subsequently. The modified Gompertz equation was used to assist in the interpretation of the conclusions. The results showed that BMP and specific methane yields were 725 and 683 mL g(-1) VSadded for KW, 470 and 214 mL g(-1) VSadded for CS, and 617 and 291 mL g(-1) VSadded for CM, respectively. Therefore, KW had the highest biodegradability of 94% as compared with CS (45%) or CM (47%). For KW mono- and co-digestion with CS, CM, or their mixture, methane production performance was better at an S/I ratio of 1.5 than that of 3.0. For CS, CM, and their mixture, S/I ratios of both 1.5 and 3.0 were suitable. A synergistic effect was found in the co-digestion process, which was mainly attributed to a proper carbon-to-nitrogen ratio and the reduced total volatile fatty acids-to-total alkalinity ratio, thus providing better buffering capacity and supporting more microorganisms for efficient digestion.