Many farmers in Flanders use a chemical air scrubber in their stables to reduce ammonia emissions. Also in biogas installations, where manure is dried, the exhaust air can be 'washed' with sulphuric acid. The by-product of this air scrubbing is discharge water containing ammonium sulphate.
With the UNIR project, Vlaco and Biogas Bree are investigating the possibilities of allowing this ammonium sulphate to break through as a replacement for chemical fertilisers in various crops.
Specifically, we want to filter and homogenise the ammonium sulphate from the discharge water, centralise its storage, optimise the usual spraying system and investigate other fertiliser application methods. In doing so, we also aim to demonstrate and disseminate the results, economic benefits and field trial observations to as large an (agricultural) audience as possible.
Partners Agropolis (VZW Boterakker), André Schelfhout (maïsteler), Bodemkundige Dienst België, Vlaco vzw, Vlaams Coördinatiecentrum Mestverwerking vzw, Broekx Landbouw- en grondwerken, Boerenbond
We can conclude that the ammonia sulphate from chemical air scrubbers is a very valuable product, certainly in typical arable farming regions and for the (larger) arable farmer with a good logistic supply. Where farmers already fertilise with fertiliser pellets, the transition to drain water may be more difficult.
An alternative way forward is to crystallise the drain water. However, this is an expensive and complex affair that can only be done on a large scale given the investment burden. Another option is to process ammonia sulphate into compost or dried digestate.