Technological solutions for converting surplus into a resource
Over the past 10–15 years, the biogas industry in the European Union has grown explosively. Germany, the Netherlands, Denmark, Italy and France have invested heavily in biogas plants as part of their energy security, climate policy and the implementation of the Green Deal. The result is clear: biogas production has increased, but with it has come a by-product – millions of tonnes of digestate. It was at this point that the system began to fail.
The first bottleneck was the EU Nitrate Directive (91/676/EEC), which severely limits the application of organic nitrogen to no more than 170 kg N/ha. In many regions, significant areas are classified as “nitrate vulnerable zones”, where additional application of even high-quality digestate is legally blocked. Formally, the fields are “oversaturated”, although the real need for organic matter in the soil often remains unmet.
The second problem is the physical form of digestate. In liquid form, it has high humidity, significant mass, and low transportability. Long-distance transportation becomes economically unviable, effectively tying the digestate to the place of production.
The third factor is the territorial imbalance. Biogas and livestock farming are concentrated locally, while crop-growing regions capable of efficiently utilizing nutrients are often beyond economically achievable logistics. The effect of a “nutrient jam” arises.
The fourth component is regulatory inertia. In a number of countries, digestate is still legally treated as waste or semi-waste, and not as a full-fledged fertilizer product. The procedures for bringing it into compliance with Reg. (EU) 2019/1009 are complex and slow, while biogas plant tanks are already being filled.
That is why the terms digestate surplus, nutrient overload, and regional accumulation problem are increasingly appearing in European reports.
However, the key realization is that the problem is not the digestate itself, but the lack of deep processing.
One of the most promising directions for solving this problem is the thermal conversion of the solid fraction of digestate into biochar. Pyrolysis or torrefaction allows to reduce the volume and weight of the product, stabilize macronutrients and carbon, bind potential pollutants and obtain a material with high sorption and agronomic value.
It is this biochar that becomes the ideal basis for organic and organo-mineral fertilizers such as GREENODIN BLACK, which combine a stable carbon skeleton, digestate nutrients, and microbiological and humification activity.
In this form, nutrients cease to be a problem of accumulation and become a long-term resource for restoring soils, increasing their fertility and carbon stability.
Paradoxically, what is currently creating tension in the EU could be a technological breakthrough for Ukraine, given the military defeat, soil degradation, organic matter shortages, and the need for independent sources of agricultural productivity. Digestate, processed into biochar and integrated into products like GREENODIN BLACK, ceases to be a “biogas waste” and becomes an element of a new circular agricultural economy.
The key technological solution to overcome the problem of digestate accumulation is its thermal conversion into biochar. It is pyrolysis that allows converting an unstable, logistically difficult product into a highly stable carbon matrix suitable for creating new generation organic and organo-mineral fertilizers, in particular GREENODIN BLACK.
General principles of the process: pyrolysis of digestate is carried out without access of oxygen, in an inert atmosphere or with pyrogas recirculation, with control of temperature and heating rate, which is critical for preserving phosphorus and potassium and forming an active porous structure of biochar.
The temperature profile of digestate pyrolysis involves:
Approximately 3% N in the final product is the optimal balance between plant nutrition and the absence of “salty” soil overload. At the same time, the enhanced version involves adding up to 5% glauconite before impregnation, which acts as a sorption “anchor” for NH₄⁺ ions, increasing the stability of nitrogen and prolonging its availability in the soil.
In such a technological scheme, digestate ceases to be a problematic waste and turns into a controlled agricultural resource, integrating into the line of fertilizers such as GREENODIN, which work not as a “one-time feed”, but as a long-term element of restoring and enhancing soil fertility and carbon balance.
Greening agro is not a fad, but a reaction to the fact that excess nutrients are becoming a source of soil and water pollution, and biodiversity loss.
Digestate with biochar and glauconite is an innovative organo-mineral composite for reducing nutrient losses, prolonged plant nutrition, and increasing soil fertility.
Soil degradation and water pollution are increasingly merging into a combined environmental crisis, especially in arid and post-industrial regions.
