Thermophilic biogas plant for dairy manure treatment as combined power and heat system in cold regions

A 60-m3 anaerobic digester was installed next to a free barn, and was operated with dairy manure at a digester temperature of 55 °C. The average loading rate in the digester was 6.75 kg/m3/day with a hydraulic retention time of 13 days. In the coldest season with an average ambient temperature of − 23 °C and manure temperature of 2 °C the average biogas production was 150 m3/day with 56% methane. Generated biogas was used to run a 15 kW generator to produce electricity, and the produced heat was collected as hot water used to maintain the digester temperature at a stable level. Daily electrical power consumption averaged at 85 kWh for the plant, while daily electricity production from generated biogas averaged at 105 kWh. Therefore the biogas plant could provide about 20 kWh/day for the farm operation.