Recovery of nitrogen and phosphorus from human urine using membrane and precipitation process

The nitrogen (N) and phosphorus (P) contents in human urine have been recovered using struvite precipitation and N-stripping techniques. Struvite precipitation technique recovers mainly phosphorus whereas N-stripping technique only recovers nitrogen. In this study, we developed an NPharvest technique which recovered both nitrogen and phosphorus separately in the same process, enabling their use independently. The technique used Ca(OH)₂ to increase the pH of urine converting ammonium into NH₃ gas and simultaneously precipitating P with Ca. The NH₃ gas is passed through a gas permeable hydrophobic membrane (GPHM) and reacts with H₂SO₄ forming ammonium sulfate. Our result showed that more than 98% (w/w) of N and P can be harvested from urine in 8 h at 30 °C. The harvested ammonium sulfate contained 19% (w/w) N, and the sediment contained 1-2% (w/w) P. The extraction of N and P from 1 m³ of urine could give a profit of 1.5 €.