Adding catalysts can usually substantially enhance pollutant
removal
during laboratory semi-batch ozonation experiments with continuous
ozone gas bubbling. However, it is unclear whether the enhanced pollutant
abatement is mainly caused by the higher •OH yields
(moles of •OH formed per mole of O3 consumed)
or the higher O3 utilization efficiency in the presence
of the catalyststwo effects that can or cannot be effectively
transferred to large-scale applications, respectively. To distinguish
these two effects during the laboratory experiments, this study compared
oxalate removal by conventional ozonation (in the absence of catalysts)
and catalytic ozonation with three carbon nanotube catalysts based
on the consumed O3 doses during the different processes.
In addition, the results of several previous studies that had evaluated
varying catalysts (e.g., NiCo2O4, MnFe2O4, and MnO2) for pollutant removal by catalytic
ozonation were revisited based on the consumed O3 doses
measured in these studies. The results show that while all the catalysts
considerably accelerated O3 transfer/consumption and pollutant
removal during catalytic ozonation than during conventional ozonation,
many of them did not enhance the extent of pollutant removal when
the same O3 doses were consumed during the two processes.
This finding suggests that in the laboratory experiments, these catalysts
only enhanced the O3 utilization efficiency but did not
significantly enhance the •OH yield from O3 decomposition during catalytic ozonation relative to conventional
ozonation. Therefore, they may not be able to enhance pollutant removal
during large-scale applications to the same extent as has been shown
in the laboratory experiments. These results indicate that to more
realistically predict the performance of catalysts for large-scale
applications, the extent of pollutant removal should be evaluated
based on the transferred/consumed O3 doses during the laboratory
experiments.
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