Urine treatment technologies yielding fertilisers as an end-product: A review

The escalating demand for agricultural fertilisers has driven interest in alternative fertiliser production technologies beyond conventional resource-intensive industrial methods. Human urine accounts for approximately 1 % of domestic wastewater by volume, but contains 80 % nitrogen (N), over 50 % phosphorus (P), and more than 60 % potassium (K) of the wastewater, making it suitable for source-separation and a viable substrate for fertiliser production. This review examines more than 20 treatment technologies for source-separated urine with a focus on fertiliser production. The technologies reviewed include: membrane processes, physicochemical technologies, microbial electrochemical systems, and hybrid approaches. For each technology, the operating principles, nutrient recovery efficiency, advantages, and limitations are outlined. This review identifies seven urine-derived fertilisers: struvite, calcium phosphate, potash, ammonium sulphate (liquid and solid), solid fertiliser (which contains N, P, K, NaCl, and KCl), and nutrient- rich liquid (which contains N, P, and K) from existing literature. Urine-derived fertilisers showed better growth in weight and size of basil plants, and demonstrated superior N and P uptake on ryegrass and maize, compared to commercial fertilisers. While treating urine with a singular technology may not simultaneously generate N, P, and K, integrating technologies can yield more than one fertiliser product with improved process efficiency. The scope and potential scalability of various urine treatment technologies are explored by analysing lab, pilot, and large-scale investigations. Further life cycle analysis is required to support real-world adoption due to the lack of studies reporting the potential impacts of implementing large-scale urine treatment facilities.