A biogas plant is an installation that allows, thanks to natural fermentation processes, to utilize the by-products of agricultural activity or agri-food processing. As a result, gas is created, often converted into electricity or heat or purified into biomethane, and the by-product is a digestate, which has fertilizing properties similar to slurry, but unlike it, is characterized by a less bothersome aroma.
Biogas plant at the University of Life Sciences in Poznań
Since 2019, the biogas plant has been operating at the Agricultural and Fruit Farm Experimental Farm in Przybroda (Poznań district), which belongs to the Poznań University of Life Sciences. In addition to managing the farm's by-products and producing fertilizer and heat for the villagers, the installation is a place where university employees conduct research.
According to Iwona Cieślik, spokesperson for the Poznań University of Life Sciences, scientists have analyzed the possibility of using nearly 20 types of digestate, a by-product of biogas plants. The question of whether we can create expensive fertilizers locally, additionally using so-called double recycling and managing unnecessary waste, while supporting the growth of cultivated plants, was answered in a film produced by the university by Prof. Witold Grzebisz from the Department of Agricultural Chemistry and Environmental Biogeochemistry of the Poznań University of Life Sciences.
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The film was made as part of the project "The best of nature 2.0. Integrated Program of the University of Life Sciences in Poznań". The project is co-financed by the European Union under the European Social Fund, Operational Program Knowledge Education Development, Measure 3.5 Comprehensive programs of higher education institutions.
Prof. Grzebisz on fertilization with digestate
As Prof. Witold Grzebisz says, biogas is the first stage of recycling in agriculture. The second is the management of digestate, which, as he emphasizes, should not be called waste, but a by-product. We should pay attention to three aspects – increasing yield, reducing costs and acting pro-environmentally.
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How should a farmer prepare for investing in a biogas plant?
The scientist emphasizes that the use of digestate should be thought out and planned. It is best to fertilize it after harvest, on the stubble, when it can easily mix the fertilizer with the soil and reduce nitrogen losses. Another solution is composting or mixing with other fertilizers to achieve a better composition.
– For example, we have a mushroom substrate that is good, but it will be even better if we add digestate to it. We can produce biofertilizers and this is the area that should be considered. Another issue is that we can dry it, but if we dry it, we use the energy that we have produced. Using digestate and its derivatives always gives a positive effect from the production point of view, because we want to obtain a higher yield, and also from the point of view of the quality of this yield – says Prof. Grzebisz.
Fertilizer prototype testing
The aforementioned project was intended to increase the fertility of poor soils and obtain larger and more stable yields on them. For this purpose, 18 fertilizer mixtures were composed, meeting the needs of different plants. They consisted of digestate, which is a nitrogen-rich biostimulant, and ash from organic waste, which is a source of calcium, magnesium, potassium, phosphorus, sodium, zinc, copper, manganese and iron.
The fertilizers were tested in the laboratory on four types of soil, where lettuce and radish were sown. The soil fertility and its changes over time were tested for 28 days. Then, two-year field tests were carried out. Fertilizers based on digestate allowed to obtain yields at least at the same level as mineral fertilizers, while being cheaper. In the case of corn, the cob grain content was found to be twice as high. Three mixtures were selected for further tests, and their introduction to the market will require further research.
