9.7. Effect of the presence of other substances
In addition to the aforementioned experimental parameters, the
presence of certain chemical substances in the oxidation medium
of photocatalytic ozonation systems can either promote or inhibit
the oxidation process and increase or decrease the oxidation effi-
ciency. Beltran et al. [68] and Garcia-Araya et al. [39] described
that the inhibitory influence of phosphate ions on photocatalytic
ozonation of sulfamethoxazole and diclofenac in water was due
to their reactions with hydroxyl radicals (as a scavenger) as well
as their role in the deactivation of the photocatalyst surface. Likewise, Santiago-Morales et al. [3] reported a lower efficiency of
hydroxyl radical formation during photocatalytic ozonation of
wastewater (compared to that of pure water), due to the presence
of bicarbonates and other radical scavengers such as phosphate
and, chloride in the wastewater. However, Tong et al. [88],
Oppenländer [96], and Zhang and Jian [97] indicated the high reaction rate constant of pollutant molecules with hydroxyl radicals or
other oxidative radicals (>10
9
L/mol s) could minimise the effect of
radical scavengers such as phosphate, bicarbonate or carbonate
ions which usually reacted with these radicals at reaction rate constants of 10
6
–10
7
L/mol s. Unexpectedly, Arana et al. [71] reported
the presence of phosphate ions in aqueous solution stimulated
photocatalytic ozonation of p-nitrophenol