9. Effects of experimental variables
9.1. Effect of pollutant concentration in water
The pollutant concentration in water is an important factor for
determining the oxidation efficiency and the synergistic effects of
photocatalytic ozonation processes. Rey et al. [51] indicated the
synergistic effects of photocatalytic ozonation on the mineralisation
of metoprolol were greater at a higher initial concentration
of this pollutant (compared with low concentrations). The variations
in the synergy parameter can also change the oxidation
mechanisms in the photocatalytic ozonation medium [9]. In most
reported cases, increasing the initial concentration of pollutant(s)
in water led to an increased oxidation rate by photocatalytic ozonation,
which was due to increased availability of pollutants for oxidative
reactions with active oxidising species, either adsorbed on
the photocatalyst or in the bulk solution. For example, the degradation
of fuel oxygenation additives in water by photocatalytic ozonation
showed that a 10-fold increase in the initial concentration of
methyl t-butyl ether (MTBE), ethyl t-butyl ether (ETBE) and t-amyl
ethyl ether (TAEE) in aqueous solution increased their degradation
rate by 14, 7.5 and 6.5 times, respectively. These differing increases
in initial oxidation rates were attributed to the different adsorption
levels and reaction rates of these fuel additives with ozone and
hydroxyl radicals [82]. Similar results were reported by Beltran
9. Effects of experimental variables
9.1. Effect of pollutant concentration in water
The pollutant concentration in water is an important factor for
determining the oxidation efficiency and the synergistic effects of
photocatalytic ozonation processes. Rey et al. [51] indicated the
synergistic effects of photocatalytic ozonation on the mineralisation
of metoprolol were greater at a higher initial concentration
of this pollutant (compared with low concentrations). The variations
in the synergy parameter can also change the oxidation
mechanisms in the photocatalytic ozonation medium [9]. In most
reported cases, increasing the initial concentration of pollutant(s)
in water led to an increased oxidation rate by photocatalytic ozonation,
which was due to increased availability of pollutants for oxidative
reactions with active oxidising species, either adsorbed on
the photocatalyst or in the bulk solution. For example, the degradation
of fuel oxygenation additives in water by photocatalytic ozonation
showed that a 10-fold increase in the initial concentration of
methyl t-butyl ether (MTBE), ethyl t-butyl ether (ETBE) and t-amyl
ethyl ether (TAEE) in aqueous solution increased their degradation
rate by 14, 7.5 and 6.5 times, respectively. These differing increases
in initial oxidation rates were attributed to the different adsorption
levels and reaction rates of these fuel additives with ozone and
hydroxyl radicals [82]. Similar results were reported by Beltran
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