EBA. Digestate as driver of the agroecological transition in Europe
A recent article published by Ghent University in collaboratiuon with the European Biogas Association, shows that digestate has a high fertiliser value and has the potential to meaningfully contribute to carbon storing in agricolture.
Anaerobic digestion (AD) is best known for the biogas it produces, as this can be converted into green energy (biomethane in primis). However, AD also produces digestate which is an excellent fertiliser containing all nutrients and micronutrients necessary for farming. As with energy recovery from biogas, the issue of digestate recovery should be a systematic part of AD project to exploit all its potential benefits. Indeed, the digestate has a double agronomic interest: making mineral elements available to plants and contributing to carbon storage in our soils.
The paper “Assessment of the Carbon and Nitrogen Mineralisation of Digestates Elaborated from Distinct Feedstock Profiles” analyses the nitrogen and carbon mineralisation rates of five of the most representative feedstock streams in the European biogas sector (pig manure, poultry manure, energy crops, sewage sludge, food waste). Nitrogen mineralisation is a biological process and vital part of soil fertility by which organic nitrogen is converted to inorganic forms which can be absorbed by plants. In agriculture, nitrogen is applied to crops in the form of fertiliser, helping them grow stronger and better. The paper shows that digestates have a high fertiliser value due to their content of nitrogen. In agriculture, nitrogen is essential to make sure plants are healthy as they develop and nutritious to eat after they are harvested. In addition to their fertilising properties, digestates have a strong potential to store carbon in the soil. The close monitoring of the mineralisation rates allowed the authors to predict the carbon sequestration potential of digestates.
The paper shows the importance of the carbon removal imprint on current and future EU policies relating to agricultural systems makes it even more pertinent to examine digestate not only from a fertilising point of view but also as a possible contributor to carbon storage.