Abstract
Dyes have always been considered in the context of recalcitrant organic pollutants in water. The present research has focused on the decolorization of Direct Blue 71 (DB71) using photocatalysis process of nano-ZrO2/UV/ Persulfate. Response surface method with central composite design was applied to determine the effects of four main factors (time, ZrO2 dosage, persulfate dosage and pH) on decolorization of DB71. The results indicated that the obtained quadratic model had a high R-squared coefficient based on the analysis of variance (ANOVA). Time had the highest effect (45.5%) on decolorization of DB71. The optimum condition predicted for complete decolorization was pH=7, 0.4 g ZrO2, 0.75 mM persulfate and 40 min reaction time. Verification experiments confirmed that there was good agreement between the experimental and predicted responses. The studied photocatalytic process could oxidize and destruct the structure of the DB71, and average oxidation state (AOS) significantly increased from −1.5 to +1.33, indicating the presence of more oxidized by-products and, consequently, improvement of biodegradability. The quenching tests showed that sulfate radical was the major agent in DB71 decolorization. It can be concluded that nano-ZrO2/ UV/Persulfate is a very effective process for decolorization of colored wastewater.
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