Use of local resources as co-substrates in a farm-scale biogas plant

Abstract

Biogas production is an established technology that is suitable for small-scale decentralized solutions, for example, on dairy cattle farms where manure is formed all year round. Cattle slurry can be co-digested with other organic biomasses to boost the production of renewable energy. The aim of this study was to outline the suitability of locally available co-substrates that are characteristic to the northern rural area in Lapland, Finland. Twelve different co-substrates originating from agriculture, reindeer meat production, fisheries and food processing were studied for their chemical characteristics and biochemical methane potential (BMP) in laboratory tests. As a result, all the tested co-substrates had a higher BMP than the cattle slurry, which could be a useful boost for farm-scale energy production. The BMP was the highest for used vegetable oil (851 l/kg VS) followed by the rainbow trout by-products (728 l/kg VS). BMP was the lowest for spoiled grass silage (265 l/kg VS) and the rumen contents of reindeer (289 l/kg VS). All substrates had high concentrations of the main nutrients, and small fish especially were rich in phosphorus (7.4 g/kg) and nitrogen (24.2 g/kg). Nutrient rich co-substrates increase the fertilizer value of digestate and the nutrient self-sufficiency of the farm.