Intellectual Property

Granular Fertiliser from Anaerobic Digester

Granular Fertiliser from Anaerobic Digester

Researchers at Queen's University, Belfast have developed methods to convert the waste liquor from anaerobic digestion (AD) into an organic granular fertiliser. The nutrients contained within the AD waste liquor are concentrated onto the solid which can be stored and transported easily, and later used as a fertiliser.



AD processes produce a large amount of waste liquor, which is commonly used as a raw liquid fertiliser on land, with associated problems of run-off, leaching and eutrophication of water courses, or which, can be costly disposed of in wastewater treatment plants. With the increased capacity in AD technology forecast, these simple disposal techniques are unsustainable.

Using, this innovative approach, the large number of nutrients contained within the AD liquor are concentrated and adsorbed onto a powdered adsorbent, which is then processed to form a low-cost, organic, granular fertiliser.

granules fertiliser  

Diagram representing the technology converting AD liquor to granular fertiliser


  • Produces an organic granular fertiliser with excellent the storage/handling properties, which can compete on nutrient capacity on a cost basis with expensive imported commercial synthetic fertilisers.
  • Nitrogen, phosphorous, potassium (N,P,K) from AD liquor are concentrated and adsorbed, allowing for a significant multi-component adsorption of nutrients.
  • Process can be adapted for waste liquors from a range of AD feedstocks.
  • Transforms a problematic waste stream from an expanding industrial sector into a valuable and locally developed "green" product, adding to the considerable benefits associated with AD.
  • Synthetic fertilisers represent a significant cost input to the agricultural sector and the cost is directly linked to fossil fuels costs which have risen by over 100% in the past year.
  • No commercial AD liquor treatment systems currently available that will produce a granular organic fertiliser.


Presently digestate liquor is described or seen as a waste, which has a negative impact on the development of AD projects in the ‘renewable energy from waste’ sector. This process can be adapted for waste liquors from a range of AD feedstuffs. This treatment system can be seen as a "bolt-on" end-of-process technology for existing AD technology suppliers.

Patent Status

An initial UK patent application (GB1113313.9) has been filed with a priority date of 02/08/2011.


Project part financed by the European Regional Development Fund under the European Sustainable Competitiveness Programme for Northern Ireland.


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