Ammonia capture from human urine to harvest liquid N-P compound fertilizer by a submerged hollow fiber membrane contactor: Performance and fertilizer analysis

Abstract

In this study, we developed a submerged hollow fiber membrane contactor (HFMC) to recover ammonia from human urine to get compound N-P fertilizers. The ammonia capture performance, water vapor transmembrane performance, ion rejection performance and the liquid fertilizer components using 1–4 mol/L H3PO4 as the stripping solution was comprehensively investigated. Increasing H3PO4 concentration did not significantly affect the ammonia capture performance but the water vapor transfer and fertilizer components. The ammonia mass transfer coefficients were in a range of 1.95×10−6±4.77×10−8 to 2.28×10−6±6.71×10−8 m/s and the ammonia flux fluctuated between 17.80 and 20.80 g/m2·h. The water vapor flux increased with the increase of stripping solution concentration and the time elapsed. The N content (21.29–55.24 g/L) was in the range of the commercial products while the P2O5 content (99.41–281 g/L) was slightly higher, which can be used in the soils or plants with a high demand for phosphorus. The liquid fertilizers were all mixtures of (NH4)2HPO4 and NH4H2PO4, but the distribution ratio slightly changed with the different initial H3PO4 concentration. The economic assessment showed that harvesting liquid N-P fertilizer from human urine using HFMC can make a profit of $7.089/L.