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

Abstract Urine with its abundant macronutrients (N-P-K) is an ideal resource for the production of fertiliser. However, the odour 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 hour. The HLSE process had vapor flux at 1.3 kg m−2 h−1 as well as high solar to vapor 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.