Effect of temperature on methane production from field-scale anaerobic digesters treating dairy manure

Temperature is a critical factor affecting anaerobic digestion because it influences both system heating requirements and methane production. Temperatures of 35-37 degrees C are typically suggested for manure digestion. In temperate climates, digesters require a considerable amount of additional heat energy to maintain temperatures at these levels. In this study, the effects of lower digestion temperatures (22 and 28 degrees C), on the methane production from dairy digesters were evaluated and compared with 35 degrees C using duplicate replicates of field-scale (FS) digesters with a 17-day hydraulic retention time. After acclimation, the FS digesters were operated for 12 weeks using solids-separated manure at an organic loading rate (OLR) of 1.4 kg VS m(-3) d(-1) and then for 8 weeks using separated manure amended with manure solids at an OLR of 2.6 kg VS m(-3) d(-1). Methane production values of the FS digesters at 22 and 28 degrees C were about 70% and 87%, respectively, of the values from FS digesters at 35 degrees C. The results suggest that anaerobic digesters treating dairy manure at 28 degrees C were nearly as efficient as digesters operated at 35 degrees C, with 70% of total methane achievable at 22 degrees C. These results are relevant to small farms interested in anaerobic digestion for methane reduction without heat recovery from generators or for methane recovery from covered lagoon digesters. (C) 2015 Elsevier Ltd. All rights reserved.