Liquid manure, fermentation residues and the high nitrate pollution of groundwater

The almost uninhibited spreading of liquid manure, solid manure and fermentation residues from biogas plants - trivialised as "commercial fertiliser" - has led to clearly excessive nitrate values in the groundwater in many places in Germany.

For this reason, the EU has already brought an action against Germany in 2016; the resulting stricter fertilizer ordinance, which should lead to a reduction in nitrate pollution, is far from sufficient to ensure compliance with the EU limits.

Following a ruling by the European Court of Justice (ECJ) last year, the federal government is now threatened with fines of EUR 860,000 per day. A further restriction of the possibility of spreading liquid manure on agricultural land is therefore to be expected.

This will inevitably lead to higher costs for farmers, as liquid manure will have to be transported over ever greater distances in regions where there is (still) no surplus of nutrients. A dairy cow typically produces 25 tonnes of manure per year. At costs of up to EUR 20/tonne for manure disposal, as is currently possible in regions with intensive livestock farming, this means additional costs of EUR 500 per dairy cow per year.

The fermentation of manure ingredients and solid manure in biogas plants can offer farmers an economical alternative to the removal of the manure. The energy obtained from the fermentation residues can be used to operate the biogas plant and to recover the nutrients it contains, e.g. by vacuum evaporation or other separation processes. This not only saves on disposal costs, but also reduces the costs for the procurement of substrates (up to now typically maize) and fertiliser costs, as the fermentation residues are processed into high-quality NPK fertilisers which can replace purchased industrial fertilisers.