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 °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 °C), on the methane production from dairy digesters were evaluated and compared with 35 °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 °C were about 70% and 87%, respectively, of the values from FS digesters at 35 °C. The results suggest that anaerobic digesters treating dairy manure at 28 °C were nearly as efficient as digesters operated at 35 °C, with 70% of total methane achievable at 22 °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.