Speaker
Description
Soilless cultivation of plants during long-term crewed space missions will be essential to produce vital supplies such as clean water, food, and oxygen while sequestering atmospheric CO2. Fertilizer replenishment during these missions will be cost-prohibitive, so nutrients will need to be recycled from waste. Human urine is being explored as a source of nitrogen and phosphorus for plants, as it contains high concentrations of both. During urine storage, its urea gets hydrolyzed, which increases the pH and triggers the precipitation of circa 30% of the phosphorus contained in the urine. No study has yet offered a thorough analysis of the speciation of this precipitated phosphorus, nor of its solubility for use as a nutrient source for plants in hydroponics.
Our research investigates precipitates issued from stored human urine and from treated human and synthetic urine. We report the complete phosphorus speciation of the urine precipitates, using X-ray diffraction, Fourier-transformed infrared, and solid-state nuclear magnetic resonance spectroscopies. We also address the extractability of phosphorus from urine precipitates using anion exchange membranes and nutrient solution at pH≈6 as predictors of phosphorus availability for plant uptake. Finally, we assess the availability of phosphorus from urine precipitates to hydroponically grown lettuce.
We found that urine precipitates are predominantly composed of well-crystallized struvite ((NH4)MgPO4·6H2O), as well as of kovdorskite (Mg2PO4·3H2O), and amorphous calcium phosphate (Ca3(PO4)2ˑxH2O). Circa 70% of the phosphorus contained in the urine precipitates was extractable for plant nutrition, most of it derived from magnesium phosphate minerals. Plant experiments are underway aiming to confirm that this 70% of extractable phosphorus contained in the precipitates is available to lettuce grown in hydroponics.
To conclude, our research offers a valuable approach to nutrient recovery in space or any closed system, while improving the current understanding of waste recycling for terrestrial crop production.
| Keywords | Plant nutrition; nutrient recovery; organic waste; human urine; hydroponic cultivation |
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