Efficient removal of ciprofloxacin in aqueous solutions by zero-valent metal-activated persulfate oxidation: A comparative study

The removal mechanisms of ciprofloxacin (CIP) in an aqueous solution using the persulfate (PS) oxidation system activated by zero-valent metals (ZVMs), such as zero-valent iron (ZVI), zero-valent aluminum (ZVA), and zero-valent copper (ZVC), were compared. The CIP removal followed the pseudo-first-order kinetics in all the PS oxidation processes mediated by the ZVMs. The influence of factors of the PS oxidation system, such as pH, and concentrations of both ZVMs and PS, was analyzed. Our results indicate that ZVI/PS process resulted in the highest removal of CIP at 84.5 +/- 1.3 % (k(obs) = 29.8 x 10(-3) min(-1)) within 60 min with pH(o) of 3.0, a molar dosage of PS at 2.25 mM and concentration of ZVI at 126 mg L-1. However, CIP was only removed to the extent of 73.3 +/- 2.5 % with k(obs) = 21.9 x 10(-3)min(-)(1) by ZVA/PS with pH(o) of 3.0, [PS](0)= 2.25 mM and concentration of ZVA at 81 mg L-1. Finally, for ZVC/PS system, the removal efficiency of CIP was lowest at 59.9 +/- 3.2 % with constant rate k(obs)= 15 x 10(-3) min(-1) when optimum conditions were initial pH of 4.0, [PS](0) = 2.25 mM and dosage of ZVC at 192 mg L-1. Based on X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) spectra, Fe2+ and Fe3+ ions from ZVI, Al3+ ions from ZVA, and Cu+ and Cu2- ions from ZVC were released by PS oxidation. Moreover, active radicals (HO*, SO4*(-)) determined as primary agents to total oxidation performance, were generated through the activation of PS by intermediate ion metals.