The application of the photo-Fenton process to the treatment of saline wastewater contaminated with hydrocarbons is investigated. Aqueous saline solutions containing raw gasoline were used as a model oil-fieldproduced water. The dependence on concentrations of the following reagents has been appropriately evaluated: hydrogen peroxide (100-200 mM), iron ions (0.5-1 mM), and sodium chloride (200-2000 ppm). The reactions were monitored by measurement of the absorption spectra and total organic carbon (TOC). Experimental results demonstrate that the photo-Fenton process is feasible for the treatment of wastewaters containing hydrocarbons, even in the presence of high concentrations of salt. The effect of the salt in this process is described through a series of reactions. A simple feedforward neural network model was found to correlate well the observed data for the degradation process.

The inhibition of the photo-Fenton (Fe2+/Fe3+, H2O2, UV light) degradation of synthetic phenol wastewater solutions by chloride ions is shown to affect primarily the photochemical step of the process, having only a slight effect on the thermal or Fenton step. Kinetic studies of the reactions of oxoiron (IV) (FeO2+) with phenol indicate that, if FeO2+ is formed in the photo-Fenton degradation, its role is probably minor. Finally, it is shown that, for both a synthetic phenol wastewater and an aqueous extract of Brazilian gasoline, the inhibition of the photo-Fenton degradation of the organic material in the presence of chloride ion can be circumvented by maintaining the pH of the medium at or slightly above 3 throughout the process, even in the presence of significant amounts of added chloride ion (0.5 M).

The photo-Fenton process (Fe(2+)/Fe(3+), H(2)O(2), UV light) is one of the most efficient and advanced oxidation processes for the mineralization of the organic pollutants of industrial effluents and wastewater. The overall rate of the photo-Fenton process is controlled by the rate of the photolytic step that converts Fe(3+) back to Fe(2+). In this paper, the effect of sulfate or chloride ions on the net yield of Fe(2+) during the photolysis of Fe(3+) has been investigated in aqueous solution at pH 3.0 and 1.0 in the absence of hydrogen peroxide. A kinetic model based on the principal reactions that occur in the system fits the data for formation of Fe(2+) satisfactorily. Both experimental data and model prediction show that the availability of Fe(2+) produced by photolysis of Fe(3+) is inhibited much more in the presence of sulfate ion than in the presence of chloride ion as a function of the irradiation time at pH 3.0.

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The photo-Fenton reaction (Fe2+/Fe3+, H2O2, UV light) is strongly inhibited by high concentrations of added chloride ion. In this work, the effect of added chloride ion on the photocatalytic step that converts Fe(III) back to Fe(II) is studied by nanosecond laser flash photolysis over a wide range of pH (1.0-3.3) and concentrations of Fe(III) (0.1-1.0 mM) and chloride ion (0.05-0.75 M). An explicit mechanistic model based on the preferential formation of the less-reactive Cl2*- radical anion via two routes (competitive photolysis of the iron(III)-chloride complex to chlorine atoms instead of the desired hydroxyl radical and pH-dependent scavenging of the hydroxyl radical by chloride ion) is proposed. This model, which fits the laser flash photolysis data for the production and decay of Cl2*- over the entire range of conditions investigated, suggests that inhibition of the photocatalytic step of the photo-Fenton process in the presence of chloride ion can be circumvented by maintaining the pH of the medium at or slightly above 3.0 throughout the reaction.

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