Sustainability-Inspired Upcycling of Organophosphorus Pollutants into Phosphatic Fertilizer in a Continuous-Flow Reactor

Abstract

With the increasing requirement for phosphorus resources and their shortage in nature, cyclic utilization of organophosphorus pollutants into phosphatic fertilizer might offer a sustainable approach to achieve the recycling of phosphorus. Herein, we first report the selective degradation of organophosphorus pollutants, via the synergistic effect of peroxymonosulfate (PMS) and sodium percarbonate (SPC), into phosphates (o-PO₄ ^3-), which are continually converted into phosphatic fertilizer by struvite precipitation on the continuous-flow reactor. Quenching experiments, electron paramagnetic resonance (EPR) results, electrochemical analysis, and density functional theory (DFT) calculation suggest that the transfer of electrons from SPC to PMS results in the synthesis of catalytically active species (i.e., ·OH, ·O₂ ^-, ¹O₂, and CO₃·^-) for hydroxyethylidene-1,1-diphosphonicacid (HEDP) degradation. For the real glyphosate wastewater, the PMS/SPC system exhibits excellent catalytic activity with 69.20% decrease in chemical oxygen demand (COD) and 37.80% decrease in the total organic carbon (TOC) after 90 min. Indeed, high performance liquid chromatography (HPLC) confirms that glyphosate is completely degraded in 90 min with the formation of 271.93 µmol/L of o-PO₄ ^3-, which is further converted into phosphatic fertilizer by the precipitation of struvite with 87.20% yield on continuous-flow reactor. Finally, biotoxicity of glyphosate to zebrafish and wheat seeds are significantly deceased after treatment of PMS/SPC system by zebrafish toxicology assays and germination tests of wheat seeds.

Keywords: Biotoxicity; Continuous‐flow reaction; Organophosphorus pollutants; Phosphatic fertilizer; Struvite.

Scheme 1

Chemical structures of HEDP and glyphosate.

Figure 1

a) HEDP degradation with different mass ratios of PMS and SPC. HEDP degradation in the presence of b) PMS and other oxidizing agent with 1:1 mass ratio and c) SPC and other oxidizing agent. d) HEDP degradation over single PMS, single SPC, and PMS/SPC system. e) Glyphosate or AMPA degradation over PMS/SPC system. f) pH Effect, g) anion effect (1 mM), h) anion effect (10 mM), and i) anion effect (20 mM) on HEDP degradation over PMS/SPC system. (Error bars are standard deviations from the statistics of three parallel experiments.)

Figure 2

a) HEDP degradation over PMS/SPC, PMS/Na₂CO₃, PMS/Na₂CO₃/H₂O₂, PMS/NaOH/H₂O₂, and PMS/NaOH system. b) Decomposition rate of PMS in HEDP degradation over single PMS, PMS/H₂O₂, PMS/SPC, PMS/Na₂CO₃, PMS/Na₂CO₃/H₂O₂, PMS/NaOH/H₂O₂, and PMS/NaOH system. c) Decomposition rate of H₂O₂ in HEDP degradation over single H₂O₂, single SPC, PMS/H₂O₂, PMS/SPC, NaOH/H₂O₂, Na₂CO₃/H₂O₂, and PMS/Na₂CO₃/H₂O₂ system. d) Inhibitor effects of NaN₃, TBA, CH₃OH, PhOH, and CHCl₃ on HEDP degradation over PMS/SPC system. e) ·OH, f) SO₄·⁻, g) ·O₂ ⁻, h) ¹O₂, and i) CO₃·⁻ EPR spectra of PMS/SPC system with TEMP and DMPO. (Error bars are standard deviations from the statistics of three parallel experiments.)

Figure 3

Optimal structure of HEDP with a) atomic number and b) electrostatic potential surface. Blue: positive; red: negative; orange spheres: P; gray spheres: C; red spheres: O; white spheres: H. c–f) Isosurfaces of the Fukui function (f⁻), f⁺, f⁰, and CDD by using Multiwfn 3.8 software.^{[ 49 ]} Blue: negative; green: positive. Isosurface value = 0.002 a.u of HEDP. H₂O was considered as the solvent during the calculation process.

Figure 4

Glyphosate degradation over PMS/SPC system a) under tap water, river water, and seawater and b) at various concentration of Cl⁻. c) The treatment of real glyphosate wastewater over single PMS, single SPC, or PMS/SPC system at 2000 dilution ratio. d) The treatment of real glyphosate wastewater over PMS/SPC system at different dilution ratio. e) The treatment of real glyphosate wastewater over different amount of PMS/SPC system at 1000 dilution ratio. f) The pH effect on the treatment of real glyphosate wastewater over PMS/SPC system at 1000 dilution ratio. g) The treatment of real glyphosate wastewater over PMS/SPC system under O₂ or Ar. h) The degradation rate of glyphosate and the formation rate of o‐PO₄ ³⁻ on the treatment of real glyphosate wastewater over PMS/SPC system at 1000 dilution ratio under pH = 11. i) Removal of TOC and COD of real glyphosate wastewater over PMS/SPC system. (Error bars are standard deviations from the statistics of three parallel experiments.)

Figure 5

a) Schematic diagram of glyphosate degradation and phosphorus recovery. b) Treatment of real glyphosate wastewater in continuous reaction system. c) Phosphorus recovery rate in continuous system.

Figure 6

a) XRD, b) SEM, c) Mg, d) O, e) P, and f) N EDX mapping of struvite recovered from real glyphosate wastewater.

Figure 7

Impacts of glyphosate (GLY) or degraded glyphosate (D‐GLY) on zebrafish embryonic development and neurodevelopment. a) 6dpf embryo survival rate (%) of zebrafish embryos exposed to 50 and 100 µmol/L GLY or D‐GLY aqueous solution. b) Hatching rate of zebrafish embryos exposed to 50 µmol/L and 100 µM GLY or D‐GLY aqueous solution. c) Heart rate per minute of zebrafish embryos exposed to 50 and 100 µmol/L GLY or D‐GLY aqueous solution. d) Tail coiling of per minute of embryos exposed to 50 and 100 µmol/L GLY or D‐GLY aqueous solution. e–g) Detection of distance moved, speed, turn angle in the locomotion test. h) Detection of speed per second in the intermittent vibration simulation test for zebrafish larvae exposed to 50 µmol/L GLY or D‐GLY aqueous solution. i) Movement distance within 1 s following vibrational stimulation. j–l) Total distance, speed, and acceleration during the intermittent vibration simulation test. Three independent replicate experiments, n = 40. Each value represents the mean ± SEM analyzed by one‐way ANOVA (*P < 0.05, **P < 0.01).