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European Biogas Association explores digestate’s contribution to healthy soils

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The European Biogas Association (EBA) has launched a comprehensive white paper exploring the potential of digestate in fostering healthy soils and advancing sustainable agricultural practices across Europe.

The further expansion of biogas production in Europe will see the generation of increasing amounts of digestate. Making the most of this valuable resource will provide significant advantages for farmers, local communities, and producers alike, including a reduction on the use of synthetic fertilisers and an alignment with EU carbon farming policies. Increasing the health of soils will also bring a considerable boost to both food production and the capturing of carbon.

The new paper explores these subjects in detail, highlighting the different types of digestate, agricultural properties and applications. It also examines the associated environmental, climatic, and soil health impacts, while also considering market strategies.

What is digestate?

During the anaerobic digestion process, biogas is produced alongside another valuable stream, called digestate. While a portion of the organics from the raw feedstock is converted to biogas during the process, the mineral fraction remains largely intact in the digestate, making it an appealing organic-mineral fertiliser.

Raw feedstocks for anaerobic digestion are largely composed of biodegradable organic matter, poorly degradable or stable organic fraction and nutrients. First, about two thirds of the biodegradable organic matter is turned into biogas, heavily reducing its share in the digestate. Second, for the stable organic fraction, the same amount is present in the digestate and raw feedstock. This stable organic fraction is particularly beneficial for soils as it serves as precursor for humus material, thus improving the clay-humus complex of soils. Thirdly, as biogas is composed of methane and carbon dioxide, fertiliser elements (N,P,K) are preserved in the digestate. Moreover, some of these elements are transformed in the AD reactor to the benefit of plant growth. For example, the organic nitrogen in the substrate is partly mineralised into ammonium, a readily available source of nitrogen for plants.

Regulatory framework

The white paper highlights several policies governing digestate at EU level include the Waste Framework Directive, the Animal By-Products Regulation, the Fertilisers Regulation, and the Nitrates Directive

Certain member states have their own specific regulations and guidelines pertaining to digestate management to address local environmental and agricultural needs (the UK regulations are available to view here). 

The EBA calls for clear legislation to maximise the benefits of digestate and to help farmers take advantage of the associated opportunities, highlighting that regulatory barriers persist, limiting its’ application. Digestate from manure can, for example, only be applied under 170 kg of nitrogen per hectare per year, whereas synthetic fertilisers can be used above this limit to reach the nitrogen requirement for each specific crop. They also point out that as long as the resource is classified as waste, its’ value is diminished, hindering its broader acceptance and utilisation.

Positive impact on environment, climate, and soil health

In summary the EBA state that digestate has the potential to support Europe’s agricultural sector in its’ transition to regenerative prac­tices and offers an attractive, sustainable alter­native to commonly used synthetic fertilisers. In addition, its’ utilisation enables a reduction in synthetic fer­tiliser usage as stipulated by the Farm to Fork strategy, has a positive impact on soil management and restoration, addresses mineral imbalances, and tackles the deficiency of organic matter in soils. Moreover, it facilitates efficient carbon capture, aligning with ongoing developments in EU car­bon farming policies.

The EBA’s white paper can be downloaded in full here.

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