Degradation of ibuprofen in soil systems by persulfate activated with pyrophosphate chelated Fe(II)

The removal of ibuprofen (IBP) by persulfate (PS) activated with pyrophosphate (SP) chelated Fe(II) was investigated. Results showed that the chelation of SP with Fe(II) can significantly trigger PS to improve IBP degradation in soil systems. Response surface methodology was applied to optimize the dosage of Fe(II)-SP and PS. The optimal dosage was Fe(II)-SP: PS = 1:10 to achieve an IBP degradation efficiency of 72.1% at an initial IBP concentration of 48.4 μM kg⁻¹. The effect of humic acid (HA) on IBP removal was also studied. A low HA concentration accelerated IBP removal efficiency, whereas a high HA concentration suppressed IBP oxidation. pH significantly impacted IBP treatment, and maximum removal was obtained at pH 5.45. The quenching test indicated that HO[rad] and SO₄^[rad]− coexisted in soil systems, although SO₄^[rad]− predominated. The steady-state concentrations of SO₄^[rad]− and HO[rad] were calculated. The effects of inorganic anions showed that Cl⁻ was concentration-dependent and HCO₃⁻ negatively influenced IBP removal from soil. A single PS addition improved the degradation efficiency of IBP, whereas a sequential injection of Fe(II)-SP was conducive to IBP oxidation. Fe(II) exhibited efficient ability to activate PS at an early stage, whereas the separate coupling of PS with seven other metal ions was less efficient. IBP transformation by-products were identified, and a reasonable oxidation pathway was schemed in accordance with gas chromatography-mass spectrometry (GC–MS) results. Soil properties were not severely impacted, and scanning electron microscopy (SEM) showed that HA was more easily oxidized than humin in soil systems.