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Electrochemical crystallization for recovery of phosphorus and potassium from urine as K-struvite with a sacrificial magnesium anode

Abstract

Declining earth resources, rising ore cost and increasing pollution are calling for recycling of wastewater in the context of the circular economy. In particular, urine is a potential source of phosphorus (P) and potassium (K), yet currently available methods for P and K recovery are limited in efficiency. Here, we designed an electrochemical crystallization system using sacrificial magnesium anodes to recover P and K in the form of K-struvite (MgKPO4·6H2O) from simulated urine at low (P/K = 0.25) and high (P/K = 0.6) phosphate levels, respectively. Results show optimal recoveries of 88.5% for P and 35.4% for K in the form of rod-shaped K-struvite at 3.5 mA/cm2, though higher current density reduced recovery due to side reactions and pH increase. Seeding prefabricated struvite crystals at 1.6 g/L into urine enhanced the recovery of K by 14.7% and of P by 23.7% compared to the control group. Overall, our findings show that electrochemical crystallization is promising to recover K-struvite fertilizers.

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Abbreviations

K:

Potassium

P:

Phosphorus

XRD:

X-ray diffractometer

SEM:

Scanning electron microscope

EDS:

Energy-dispersive spectroscopy

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Acknowledgements

We gratefully acknowledge the co-funding of this work by the National Natural Science Foundation of China (No. 52070130) and the Shuguang Project of Shanghai (Education and Scientific Research Project of Shanghai, 18SG45).

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Correspondence to Hongbo Liu.

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Shan, J., Liu, H., Long, S. et al. Electrochemical crystallization for recovery of phosphorus and potassium from urine as K-struvite with a sacrificial magnesium anode. Environ Chem Lett (2021). https://doi.org/10.1007/s10311-021-01333-5

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Keywords

  • Electrochemical crystallization
  • Sacrificial anode
  • Urine
  • Nutrient recovery
  • Struvite