NPHarvest – Sustainable recycling of phosphorus and nitrogen - Sweden Water Research

NPHarvest – Sustainable recycling of phosphorus and nitrogen

NPHarvest is a technology, developed by Aalto University, to extract phosphorus and nitrogen from highly concentrated wastewater streams such as digested black water or reject water from the digestion of sewage sludge. The technology has been tested on a pilot scale at RecoLab.

NPHarvest consists of a pre-treatment with calcium hydroxide which results in the precipitation of phosphorus in a sludge-like phosphorus product, followed by a nitrogen recovery step where ammonia passes through a hydrophobic gaspermeable membrane, reacts with an acid and forms an ammonium salt.

NPHarvest extracts 95% phosphorus and at least 50% nitrogen. Ammonium sulphate from NPHarvest is a pure product with a high nitrogen content, and it falls within the scope of the upcoming updates within the EU regulation for recycled fertiliser products (EU 2019/1009). The phosphorus product contained only 1% phosphorus with a contaminant content well below current limit values for sludge spreading on agricultural land. This phosphorus product does not currently fit into the categories of the new EU regulation. The largest environmental impact for NPHarvest was shown to origin from emissions of ammonia and production of calcium hydroxide and electricity. Future development of the technology should consider closed reactors to avoid direct air emissions and evaluate alternatives to the use of calcium hydroxide. In addition, drying of the ammonium salt should be done with energy-efficient techniques.

The project was partially financed by Swedish Water & Wastewater Association Development Fund (project number 20-120) and J. Gust. Richert Foundation.

Final report (in Swedish)

Högstrand, S., Uzkurt Kaljunen, J., Kjerstadius, H., Al-Juboori, R., Jönsson, K., Mikola, A., Peters, G. & Svanström, M. 2022. Rejektvattenrening med näringsåtervinning – Teknisk och miljömässig bedömning av NPHarvest-teknologin genom pilotförsök och livscykelanalys. In Swedish. Svenskt Vatten Utveckling. Rapport nr. 2022-12. (only available for Swedish Water and Waste Water Association until March 2023)