Nitrogen recovery from cHTG process water

Nitrogen is an essential nutrient for food production. However, the method currently used to produce nitrogen fertiliser is highly energy-intensive and dependent on fossil fuels. Our innovation focuses on recovering nitrogen from the process water produced during catalytic hydrothermal gasification and transforming it into valuable fertiliser products, thereby closing the nutrient loop and reducing reliance on fossil fuel-intensive synthetic fertilisers while reducing the waste from the gasification process.

The study explores three pathways for the process water:

1. Direct Use as Fertilizer: The quality of the process water is assessed to ensure it meets the required standards for direct agricultural application (e.g. heavy metals). Ammonium hydrogen carbonate is generally considered to be a poor-quality fertiliser due to its instability. Composition variability presents additional challenges for consistent and safe use.
    
2. Treatment for Nutrient Recovery: This option involves converting nitrogen into a more suitable form, such as ammonium sulphate or ammonium nitrate, and increasing its concentration or precipitating it as a solid. Several treatment pathways are evaluated, including physical processes (e.g. stripping), chemical or electrochemical processes (e.g. ion exchange) and biological treatment (e.g. nitrification).
    
3. Wastewater Treatment Plant: In this option (benchmark), process water is discharged to the wastewater treatment plant.