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New report: Best available technologies for pig manure biogas plants

Leaching of nitrogen and phosphorus from intensive pig production can be reduced if the large quantities of manure are used for biogas production and if the digestate is spread in springtime when the crops grow and utilize the natural fertilizer efficiently. According to a new report from Baltic Sea 2020, the right setup of technologies for biogas production and proper treatment of the digestate can benefit both water quality and climate.

The study aims to reduce leaching of nutrients to the Baltic Sea from intensive pig production. The strategy is to identify and describe best available technologies to digest pig manure and efficiently recirculate the nutrients as fertilizer to the crop production. Digestion makes nitrogen better available for the plants and a more efficient fertilizing can be achieved, provided that dosage of nutrients is according to plants need.

According to Thorkild Qvist Frandsen from AgroTech, nutrient flow calculations show that the readily available nitrogen in one ton of pig manure increases from 2,6 kg to 3,4 kg during digestion. More nitrogen can therefore be taken up by the plants and less leaches to surrounding waters. The risk for leaching of nutrients to air and water increases if manure is spread during autumn when the plant uptake is less efficient. The risk increases a bit with digested manure.

Lena Rodhe from JTI - the Swedish Institute for Agricultural and Environmental Engineering argues that covered storage is needed to avoid emissions of ammonia, and large enough to allow for spreading the digestate in springtime. She states that a spreading technology which quickly incorporates the digestate into the soil should be used.

The report also recommends separation of slurry or digestate in order to facilitate dosing of nutrients in accordance to crop needs. The resulting solid fraction should be stored as short time as possible in covered containers to reduce the risk for evaporation of ammonia and laughing gas (N2O).
Knud Tybirk from Agro Business Park states that an efficient use of the valuable nutrient resource in livestock manure requires the right dosage of the digestate to the fields. This requires standard values for the concentrations of nutrients in livestock manure. Though, he stresses that these are unfortunately not yet available in all countries around the Baltic Sea.

The report ”Best Available Technologies for pig manure biogas plants in the Baltic Sea Region” was produced in collaboration between experts from AgriFood Research - Finland, Agro Business Park - Denmark, AgroTech – Denmark and the Swedish Institute for Agricultural and Environmental Technology. The project is initiated and financed by Baltic Sea 2020. The full report can be downloaded at

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