Fertiliser recovery from source-separated urine via membrane bioreactor and heat localized solar evaporation

Urine with its abundant macronutrients (N-P-K) is an ideal resource for the production of fertiliser. However, the odor and pathogens in the raw urine must be removed to meet the public acceptance of urine collection systems and to enable its safe reuse as a fertiliser. In this work, real urine was collected and treated through a pilot-scale gravity-driven membrane bioreactor (GDMBR) to remove the malodorous organics and to nitrify almost 50% of the ammonia into nitrate. The stablised urine was subsequently distilled via low-cost heat localized solar evaporation (HLSE) to produce a non-odorous solid fertiliser. The developed HLSE with a small footprint can attract bulk solution into a vertical insulated space and quickly heat it up to 68 °C within 1 h. The HLSE process had vapour flux at 1.3 kg m^-2 h^-1 as well as high solar to vapour conversion efficiency at 87%. Based on the EDX mapping and XRD analysis, the generated crystals are mainly NaNO₃, NH₄Cl, NaCl, NH₄H₂PO₄ and K₂HPO₄, which are ideal nutrients for vegetation. In this study, the produced urine-derived fertilisers have a better performance on the growth of the leafy basil than the all-purpose commercial fertilisers. Generally, the GDMBR-HLSE is a promising cost-effective and green technology for nutrients recovery from urine.