Evaluation of three reagent dosing strategies in a photo-Fenton process for the decolorization of azo dye mixtures

Abstract

Three reagent dosing strategies used in the solar photo-assisted decolorization of a mixture of sulfonated dyes consisting of acid blue 113, acid orange 7 and acid red 151 were evaluated. Results demonstrated that the dosing strategy influenced both reagent consumption and the biodegradability and toxicity of the effluent. In one strategy (E1), the Fenton's reactants were dosed in a punctual mode, while in the other two strategies (E2 an E3), the reactants were dosed continuously. In the E2 strategy the reactants were dosed by varying the duration of the injection time. In the E3 strategy, the reactants were dosed during 60min at a constant rate, but with different concentrations. All cases showed that feeding the reactor between 40% and 60% of the maximal dose was sufficient to decolorize more than 90% of the mixture of azo dyes. The E1 strategy was less effective for aromatic content reduction. Conversely, the continuous addition of the reagents (E2 and E3 strategies) improved the aromatic content removal. E3 strategy was substantially more appropriate than E1 strategy due to improved the effluent quality in two key areas: toxicity and biodegradability.