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...[
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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 (Y
1) and cost for unit CBZ removal (Y
2). On condition of
achieving over 70% of Y
1, the optimum conditions for the lowest Y
2 were: a UV dose at 265.5 mJ/cm
2 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 Y
1 and Y
2 were 71.44% and 0.0102
HK$/%/m
3, 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, [Fe
3O(cit)
3H
3]
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 SO
4•–
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 SO
4•– 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.
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