Carbamazepine (CBZ), a persistent emerging contaminant, has become a worldwide concern because of its potential toxicity and frequent occurrence in groundwater. In this work, degradation of CBZ in the Fe(II)/citrate/UV/persulfate (PDS) and Fe(II)/citrate/UV/peroxymonosulfate (PMS) processes at neutral pH was investigated. CBZ degradation was enhanced by adding a small amount of Fe(II) and further enhanced by premixing Fe(II) with citrate in both processes at neutral pH. The enhancement was only additive in the Fe(II)/citrate/UV/PDS process, while it is synergistic in the Fe(II)/citrate/UV/PMS process, as the observed CBZ degradation was higher than the sum of that by the citrate/UV/PMS and Fe(II)/citrate/PMS processes. The synergism in the Fe(II)/citrate/UV/PMS process was furt...[ Read more ]

Carbamazepine (CBZ), a persistent emerging contaminant, has become a worldwide concern because of its potential toxicity and frequent occurrence in groundwater. In this work, degradation of CBZ in the Fe(II)/citrate/UV/persulfate (PDS) and Fe(II)/citrate/UV/peroxymonosulfate (PMS) processes at neutral pH was investigated. CBZ degradation was enhanced by adding a small amount of Fe(II) and further enhanced by premixing Fe(II) with citrate in both processes at neutral pH. The enhancement was only additive in the Fe(II)/citrate/UV/PDS process, while it is synergistic in the Fe(II)/citrate/UV/PMS process, as the observed CBZ degradation was higher than the sum of that by the citrate/UV/PMS and Fe(II)/citrate/PMS processes. The synergism in the Fe(II)/citrate/UV/PMS process was further investigated. CBZ degradation increased with the increasing concentrations of Fe(II), PMS, and the citrate/Fe(II) ratios. The optimum treatment conditions were obtained using response surface methodology (RSM) in terms of two responses, CBZ removal efficiency (Y₁) and cost for unit CBZ removal (Y₂). On condition of achieving over 70% of Y₁, the optimum conditions for the lowest Y₂ were: a UV dose at 265.5 mJ/cm² and concentrations of Fe(II), PMS and citrate at 12.2 μM, 100 μM and 26.4 μM, respectively. Under the optimum conditions, the predicted Y₁ and Y₂ were 71.44% and 0.0102 HK$/%/m³, respectively. These values matched the experimental results well and indicated that RSM successfully predicted the optimum conditions for the degradation of CBZ. In addition, the presence of NOM and alkalinity inhibited the degradation of CBZ, while NH4⁺, Cl^- and Br^- did not affect the degradation of CBZ.

The synergism of the CBZ degradation was mainly attributed to the regeneration of Fe(II) from the Fe(III)-citrate complex, [Fe₃O(cit)₃H₃]^2-, driven by the UV irradiation in the Fe(II)/citrate/UV/PMS process. In general, the degradation of CBZ can be treated as a two-stage process with the generation of SO₄^•– and •OH as main reactive oxygen species in the process. In the first stage, about 11% of CBZ was degraded within the first second due to the fast reaction between Fe(II) and PMS. While in the second stage, UV and the regenerated Fe(II) activated PMS to produce SO₄^•– and •OH that contributed to the CBZ degradation, which followed the pseudo-first order kinetics at a rate constant of 1 × 10^-3 s^-1.