Asker, Norway: New research studies from Aarhus University (Denmark) on NEO (Nitrogen Enriched Fertiliser) demonstrate a substantial reduction in ammonia emissions from field application and chemical stability of NEO for six months.

The research studies explores plasma treatment as a solution for enhancing the fertilizer value of digestates from biogas plants, while reducing the nitrogen emissions associated to the biogas digestate. Aarhus University (AU) Foulum holds the largest biogas test centre in the world.

Read about the project here.

Long term storage and field application 

In March 2022 a collaboration started between the University and N2 Applied to assess N2 Applied’s plasma technology alongside the AU Foulum biogas plant’s existing operations for additional value creation and reduced emissions. 

The first study1 – led by Postdoc Jared Onyango Nyang’au – analysed the chemical stability of NEO, in long term storage, and after field application.  

The work demonstrated that, when treated to a pH of 5, the pH of NEO at the end of a six-month period was still below 6.  

-This is important as a pH of 6 and above has the potential to lead to ammonia emission. The work concludes that integrating plasma treatment with biogas plants is a promising solution for agriculture, says Kenny Brown, Senior Researcher – Agronomy and Environment at N2 Applied. 

Reduction of ammonia emissions 

Johanna Pedersen, a Tenure Track researcher, undertook work to measure the ammonia emissions from applying NEO to the field to mimic fertiliser application. This work demonstrated ammonia emissions reductions from 70-89% when implementing the plasma technology. Interestingly, it was also demonstrated that the surface soil pH was lower after NEO application.  

-Maintaining this low pH explains the positive effect of plasma treatment in ammonia emissions from field application, says Kenny Brown. 

Using the NEO produced at Foulum, field trial studies were completed by Martin Nørregaard Hansen, Chief consultant in Crops and environmental research at SEGES Innovation. The work was completed as part of a running ‘Landsforsøg’. Landsforsøg (field trial studies) are a series of yearly field trials carried out by the Crop and Environment Innovation Centre at SEGES Innovation in Denmark. The results of the studies are used to inform Danish farmers on the latest technology advancements in their fields. 

Field trial: The machines used to measure the field emission at the research studies conducted at Aarhus University in Denmark. Kenny Brown, Senior Researcher – Agronomy and Environment at N2 Applied, and Johanna Pedersen, Tenure Track Researcher, Department of Biological and Chemical Engineering at Aarhus University.  

NEO vs organic slurries 

The field trial studies produce yield responses and mineral fertilizer equivalent (MFE) values of different types and treatments of organic fertilisers. The MFE value describes the efficiency of the nitrogen content of an organic fertiliser compared to the nitrogen efficiency of a chemical fertiliser.  

-For example, if an organic fertilizer has a MFE value of 50, it means that 100 kg of nitrogen in the organic fertilizer gives equivalent nutrient and fertilizer value as 50 kg of nitrogen in a chemical fertilizer. The MFE calculation is using Total Nitrogen, which includes both organic nitrogen and plant available nitrogen, explains Kenny Brown. 

The trial in 2022 investigated 6 different organic slurries. One of these were solid-liquid separated digestate. The fertilization effect of this type of slurry was studied with and without subsequently NEO treatment. This year the MFE value of the separated digestate was 20, whereas the MFE value was 53 when the digestate was treated by the NEO treatment.  

The fertilization effects of the NEO treatment of separated digestate were repeated in 2023. This year the NEO treatment increased the MFE of separated digestate from 61 to 96. The results demonstrates that the fertilization effects of NEO treated separated digestate can be almost as high as the fertilization effects of a chemical fertiliser. *The translated tables from the 2022 and 2023 LANDSFORSØGENE reports can be found at the bottom of this text. 

The two years of trial results were vastly different, but positive for separate reasons, explains Kenny Brown. 

– The trial 2022 demonstrated the potential of NEO to protect yields in years where the environmental conditions mean organic slurries perform particularly badly. Whereas the 2023 result demonstrated that NEO performs as well as a commercial fertiliser, where the untreated slurry lose 39 percent of their fertilising potential. When the organic to mineral nitrogen ratio is considered, NEO is shown to outperform the chemical fertiliser in terms of applied mineral nitrogen, says Kenny Brown. 

The collaboration at AU Foulum is part of the GUDP MAG project: ‘Metoder til reduktion af Ammoniaktab og øget metanudbytte fra biogasGylle’, or Methods for reducing ammonia loss and increased methane yield from biogas digestate. This project investigates and assesses further introduction and development of the processes and techniques that can reduce ammonia emissions related to biogas operations. 

– These separate research articles demonstrate that plasma treatment enriches the digestates with nitrogen, stabilizes pH, and reduces emissions during field application, and is a better fertiliser. This mean less nitrogen is lost as a pollution both in storage and on the field. And when considered with the additional benefits to the wider environment it highlights the positive impacts plasma treatment can have on the agronomic and environmental potential of a farm says Kenny Brown at N2 Applied. 

Additional information about the trials 

Translated tables taken from the Landsforsøgene reports from 2022 and 2023. The tables describe the application of the slurry treatments,  the chemical properties of the slurry aswell as the MFE achived for all treatments. 

Refrence list 

  1. Nyang’au, J. O., Sørensen, P. & Møller, H. B. Effects of plasma treatment of digestates on pH, nitrification and nitrogen turnover during storage and after soil application. Environ. Technol. Innov. 34, 103578 (2024).
  2. Pedersen, J., Labouriau, R. & Feilberg, A. Effect of slurry separation and air-plasma treatment on NH3 and VOC emissions from field applied biogas digestate and pig slurry to grassland. Biosyst. Eng. 247, 257–266 (2024).
  3. SEGES Innovation. Landsforsøgene 2022. https://www.landbrugsinfo.dk/public/b/1/7/landsforsogene.
  4. SEGES Innovation. Landsforsøgene 2023. https://www.landbrugsinfo.dk/public/b/1/7/landsforsogene.