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Drain water reused as fertiliser

The UNIR project by Biogas Bree collects drain water from the chemical air washers of biogas installations and pigsties in Limburg in a centralised manner, and guarantees standardised treatment. It brings together farmers like André Schelfhout in a machine ring, with users sharing an optimised sweep hose and ammonium sulphate fertiliser. This allows for the recovered nitrogen to replace the imported mineral fertiliser, which reduces the environmental footprint of nitrogen fertiliser.

In Flanders approximately 12,000 m³ of drain water - that equals about 500,000 kg of nitrogen - is produced by chemical or biological air washers. These quantities increase every year, partly because of the stricter emission standards. This increase in recovered, highly efficient nitrogen and sulphur goes hand in hand with a high demand for fertiliser, and on the other hand, paradoxically it comes with enormous imports of chemical nitrogen. The opportunity to recover and reuse nitrogen and sulphur locally as ammonium sulphate, which does not contain phosphor, is no easy feat. About three quarters of Flemish agricultural plots are grass, corn, grass/corn, and potato and beet fields. These crops require relatively high to high nitrogen levels. Corn alone is cultivated on 20% of all agricultural fields in Flanders. The north east of Limburg is the area with the highest levels of corn cultivation, so there is great potential for the use of ammonium sulphate. UNIR offers four circular solutions.

  • Central storage of drain water will result in a more homogeneous product that is readily available.
  • Filtering through a tried and tested filtering system to remove impurities, guaranteeing optimised use.
  • Optimised side dressing via sweeping hoses is more efficient, does not damage the soil and does not ‘burn’ the crops.
  • Involving both farmers (via Agropolis, an incubator for agro-innovation, and Boerenbond, the Farmers’ league), contract workers, platform organisations of biogas plants and manure processors is an important step forward, boosting the potential of local agricultural chains.

Biogas Bree

Partners Agropolis (VZW Boterakker), André Schelfhout (maïsteler), Bodemkundige Dienst België, Vlaco vzw, Vlaams Coördinatiecentrum Mestverwerking vzw, Broekx Landbouw- en grondwerken, Boerenbond