The major part of this work is devoted to the examination of the degradation of Ponceau S (PS) in aqueous medium by using the photo-Fenton process. The influence of pH of the medium, oxidant dose (H2O2), ferrous ion dose and the presence of inorganic ions such as bicarbonate, sulphate and nitrate on degradation kinetics was also analyzed. Before that, the efficiency of this process was compared to three other advanced oxidation processes (AOPs) such as H2O2/UV, Fenton (Fe2+/H2O2), and solar photo-Fenton. It was found that all dye degradation kinetics obeyed a pseudo-first order, and their apparent rate constants were represented by the ratios: kapp (H2O2/UV/Fe2+) =0.295 kapp (sunlight/Fe2+/H2O2) =0.141 kapp (Fe2+/H2O2) = 0.111 kapp (H2O2/UV) =0.031.Under reference conditions (0.06 mM of PS in ultrapure water), photo-Fenton oxidation using 0.06 mM of Fe2+, 1mM of H2O2 and the pH optimal value of 3 yielded more than 94.3% in only10 min of dye degradation with an apparent rate constant of 0.2951 min-1. Elsewhere, the addition of the salts in aqueous medium has, in general, an inhibition effect on the decolorization kinetics due to controlled ionic interactions of metals with inorganic ions. The most adverse effect on PS disappearance rate was observed when bicarbonate ions were present in the treated medium.
The purpose of this study was to apply the experimental Box–Behnken design (BBD) to evaluate the effect and, therefore, the optimal values of three chosen factors on the efficiency of the UV/H2O2 process to decolorize Ponceau S (PS) aqueous solutions. The factors studied at three levels were the irradiated volume of dye solution, the dye solution turbidity and the H2O2 dosage. The equations generated, analysis of variance (ANOVA), contour plots and response surface plots were used to analyze the relationship between independent variables and the outcomes of experiments. The fitted model was significant, with an adjusted coefficient of determination (adj-R2 = 0.9835). The results showed that factors such as H2O2 dosage and irradiated volume were the main parameters that affected the decolorization efficiency of the PS aqueous solution, while the turbidity had a slight effect on the response. In addition, significant values were obtained for irradiated volume and H2O2 dosage interaction and square terms of all studied factors. Furthermore, the optimal conditions for decolorization of the PS aqueous solution were found to be an irradiated volume of 257.59 mL, a turbidity of 13 NTU and an H2O2 dosage of 1.76 mM.
The photocatalytic oxidation using the highly reactive hydroxyl radical from UV/H 2 O 2 system is one of the advanced oxidation processes (AOPs) that destroy or even mineralize organic pollutants, which are harmful to the environment. However, certain costs must be controlled by taking into account influencing factors such as the dose of irradiance, oxidant dosage, and the complexity of the background matrix, among others. The objective of this work was to optimize Ponceau S (PS) degradation efficiency by UV/H 2 O 2 process in artificial seawater by using central composite design (CCD). The three selected factors were the hydrogen peroxide concentration, the irradiated volume and the PS dosage. The regression analysis showed good fit of the experimental data to the second-order polynomial model with a correlation coefficient (R 2 ) of 0.9612. The optimal conditions were found to be: [PS] = 50.91 mg/L, [H 2 O 2 ] =2.24 mM, and irradiated volume = 600 mL. Under these conditions, the PS decolorization efficiency was equal to 72.47%.
Generation of anion sulfate radicals (SO4•−) and hydroxyl radicals (HO•) by UV/Persulfate and the UV/Peroxydate processes have been successfully studied to degrade Ponceau S dye. Under [PS] = 0.06 mM; [H2O2] = 2 mM; [S2O82-] = 2 mM, the UV/Persulfate process was effective (kapp = 0.163 min−1) than the UV/Peroxydate process (kapp = 0.054 min−1). The lack of dissolved oxygen, the excess of hydrogen peroxide (H2O2) dosage at 2 mM, and the alkaline pH of 10.01 significantly reduced the UV/Peroxydate efficiency. The scavenging effect of the hydrogenocarbonates and nitrates on the PS dye degradation by the UV/Persulfate process was significant, whereas chlorides had a slight influence. The composition of seawater in chlorides, sulfates, carbonates, and bromides decreased the photoactivity of the studied processes. The presence of phenol showed that the reactive affinity of the (HO•) is more superior to the SO4•−. The UV/Persulfate process achieved 82.35% of chemical oxygen demand removal against 59.56% for the UV/Peroxydate in about 100 min. This study demonstrated that the UV/Persulfate process is a viable option for PS dye degradation. To the best of our knowledge, this is the first report for studying the PS dye degradation under some varying new operational factors. However, the identification of by-products, their nature, and their concentration requires special attention.
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