Reduction of Greenhouse Gas Emissions by Replacing Fertilizers with Digestate

Digestate from a biogas plant can be a valuable organic and mineral fertilizer. Quantitative proportions of co-substrates used in three agricultural biogas plants in Poland were analyzed. The composition of digestates was examined and large differences in the content of macronutrients were found, especially N and K. On the basis of the factors used to calculate emissions from the production and use of artificial fertilizers, the GHG reduction resulting from replacing mineral fertilizers with digestate was calculated. In terms of 1 Mg of fresh digestate, this reduction may not seem large, as it amounts to 27.9-61.6 kg of CO2 eq, but it should be taken into account that digestate contains little dry matter. The annual amount of digestate used on an area of 1 ha allows avoiding GHG emissions of 25.8-44.5 Mg CO2 eq.