Pig poo powers biogas plant

German plant builder WELTEC BIOPOWER has collaborated with Finnish partner Doranova to complete a biogas plant near Turku in south-western Finland, a region characterised by livestock farms. The 250 kW plant — belonging to a group of three pig farmers — runs entirely on liquid manure.

Environmental policy in Finland is increasingly based on sustainable nutrient recycling, with agriculture playing an important role in regions with intensive animal husbandry. While manure and slurry might be regarded as waste in other parts of the world, the Fins rely on the advantages of the so-called black gold. Fertilisation with this organic substance improves the structure of soil and increases carbon storage in the ground. Moreover, an upstream biogas process delivers climate-neutral energy and ensures better plant availability of the fertiliser.

The farm structure and location of the Finnish pig farmers present an ideal setting for the anaerobic digestion project. Currently, about 40,000 t of pig manure is available as input material for the stainless steel digester, which has a capacity of 4903 m³.

The heat generated by the 250 kW CHP unit is used to preheat the liquid manure, which is first buffered in an upstream slurry pit. To minimise the loss of heat in the harsh Finnish winter, WELTEC equipped the digester cladding with an extra-thick insulation layer. This will result in a more efficient digestion process.

The fully automated operation culminates in the separation of the digestate. By compressing the nutrients, the transportability is increased and this helps to balance any regional nutrient surpluses and reduce the entry of these nutrients in the Baltic Sea and other bodies of water.