Costs of slurry separation technologies and alternative use of the solid fraction for biogas production or burning – a Danish perspective

The purpose of this paper is to analyse different separation concepts in order to evaluate the overall costs based on a systems approach from stable to field. When livestock are produced in livestock intensive areas the distribution of manure without creating a surplus of nutrients is often a problem. Separation of the slurry into a liquid nitrogen rich fraction and a more solid phosphorus rich fraction, which is exported away from the farm, may alleviate this problem. Separation offers an alternative to transporting the slurry further away, renting more land or buying more land. The need for P-balance is stricter in Denmark than before, but developments in feeding, changes in regulation and the reduction of livestock numbers in Denmark have made separation less favourable. This article compares dominant separation technologies in Denmark, such as decanter and flocculation, as well as source separation, in order to establish the overall costs. Key parameters are livestock density, transport distance, price of additional land and cost of separation. The conclusion is that unless land prices or prices on slurry agreements are very high, traditional handling of animal manure has the lowest costs. Decanter separation can be the cheapest if area is limited and co-operation with neighbours is possible as large volumes reduce separation costs per tonne. Flocculation is the best if much P has to be removed from the farm in the solid fraction. Separation will in the future in many cases be combined with biogas production as the solid fraction gives a much higher gas production per tonne than slurry.