Treatment in a biogas plant has several positive effects for the environment. One of which is the treated organic waste output, called digestate. This decomposed material can replace appropriate amounts of synthetic mineral fertiliser. Synthetic mineral fertiliser adds nutrients to the cycle while digestate uses the nutrients already available in the cycle. The carbon – nitrogen rate (C/N-rate of 8-10) of the digestate means that nitrogen is easily available for the crops. The use of digested material after the biogas production process removes not only phosphorous and nitrogen from the sea and enables carbon fixation, it also serves as fertiliser for crop plants and supports the nutrient cycle.
Digestate is sustainable because high amounts of phosphate can be delivered back without loss into the nutrient cycle and, as mentioned, nutrient sources from outside the cycle can be replaced – reducing the total nutrient load. Moreover, the fertilisation with digestates delivers lower amounts of climate relevant gases into the atmosphere compared to the input of raw liquid manure. In the long term the output of digestates promotes a positive topsoil development with good soil fertility and the digestate contains easily-available nitrogen, phosphorous and potassium for the crops. By this regard the digestate from biogas plants can contribute to a functional recycling management and a generation of permanent, sustainable and near-natural nutrient cycles is possible (in terms of permanent agriculture – permaculture).