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Removal of the X‑ray Contrast Media Diatrizoate by Electrochemical Reduction and Oxidation
journal contribution
posted on 2013-12-03, 00:00 authored by Jelena Radjenovic, Victoria Flexer, Bogdan
C. Donose, David L. Sedlak, Jurg KellerDue
to their resistance to biological wastewater treatment, iodinated
X-ray contrast media (ICM) have been detected in municipal wastewater
effluents at relatively high concentrations (i.e., up to 100 μg
L–1), with hospitals serving as their main source.
To provide a new approach for reducing the concentrations of ICMs
in wastewater, electrochemical reduction at three-dimensional graphite
felt and graphite felt doped with palladium nanoparticles was examined
as a means for deiodination of the common ICM diatrizoate. The presence
of palladium nanoparticles significantly enhanced the removal of diatrizoate
and enabled its complete deiodination to 3,5-diacetamidobenzoic acid.
When the system was employed in the treatment of hospital wastewater,
diatrizoate was reduced, but the extent of electrochemical reduction
decreased as a result of competing reactions with solutes in the matrix.
Following electrochemical reduction of diatrizoate to 3,5-diacetamidobenzoic
acid, electrochemical oxidation with boron-doped diamond (BDD) anodes
was employed. 3,5-Diacetamidobenzoic acid disappeared from solution
at a rate that was similar to that of diatrizoate, but it was more
readily mineralized than the parent compound. When electrochemical
reduction and oxidation were coupled in a three-compartment reactor
operated in a continuous mode, complete deiodination of diatrizoate
was achieved at an applied cathode potential of −1.7 V vs SHE,
with the released iodide ions electrodialyzed in a central compartment
with 80% efficiency. The resulting BDD anode potential (i.e., +3.4–3.5
V vs SHE) enabled efficient oxidation of the products of the reductive
step. The presence of other anions (e.g., chloride) was likely responsible
for a decrease in I– separation efficiency when
hospital wastewater was treated. Reductive deiodination combined with
oxidative degradation provides benefits over oxidative treatment methods
because it does not produce stable iodinated intermediates. Nevertheless,
the process must be further optimized for the conditions encountered
in hospital wastewater to improve the separation efficiency of halide
ions prior to the electrooxidation step.