Optimization of parameters applied to degradation and mineralization of p-nitrophenol using advanced oxidative processes

Advanced oxidative processes are widely used in the degradation of organic compounds. The degradation and mineralization of the PNF was evaluated by means of an experimental factorial design, using photolysis (UV) and 28 photo-peroxidation (UV/H 2 O 2 ). With the results optimized, degradation kinetics was performed and the 29 experimental data adjusted to mathematical models. In the UV system, it was possible to degrade just over 65% 30 and mineralize 15% over 7 h of reaction; however, with the addition of the oxidizing agent H 2 O 2 , it was possible 31 to obtain 100% removal of the contaminant, suggesting that there was no formation of intermediate compounds. 32 Kinetics results fitting the first order model and the velocity constants revealed that degradation is extremely faster 33 in the UV/H 2 O 2 system (k 1 , UV/H2O2 = 0.0580 min -1 > k 1 , UV = 0.0018 min -1 ).


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Degradation of the quality of aquatic systems due to the disposal of toxic liquid waste is a significant  Saka and Tekintas 2020). In Brazil, the maximum level of phenols allowed is only 0.5 mg L -1 (Brasil 2011 (Table 1). In the UV-only experiments, the PNF concentration (10-100 mg L -1 ) and height of 85 the water depth (1.5-3.5) were the variables evaluated, while in UV/H 2 O 2 , the PNF (10-150 mg L -1 ) and H 2 O 2 (10-86 100 mg L -1 ) concentrations were evaluated. For photo-peroxidation, the liquid blade was fixed at 2.5 cm (best UV 87 result

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The experimental data was treated using the Statistica 12.0 (StatSoft, Tulsa, USA) and the results were 106 validated with analysis of variance (ANOVA). The response surface methodology (SRM) obtained an optimization 107 of the advanced oxidation processes, with 95% confidence (p-value < 0.05).

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where Ci and Ce are the initial and equilibrium concentration of PNF (mg L -1 ), t is the reaction time (min). The 115 velocity constants k 1 (min -1 ), k p1 (min -1 ) e k 2 (L mg -1 min -1 ) refer to the FO, PFO and SO models.

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In the Pareto diagram (Fig. 3), it is possible to visualize the influence of the studied variables in the applied 151 treatments. As a planning response, for the degradation in the UV-only system (Fig. 3a),  (Table SM1) confirms 182 that these results are statistically significant (Fcalc> Ftab) and reliably represent the results (Fig. SM1).

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The optimal range for degradation in the UV/H 2 O 2 process (Fig. 4b)

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In the Pareto diagram (Fig. 6), it can be seen that, in the mineralization process using the UV-only system 238 ( Fig. 6a), there was no significance for the studied variables, PNF concentration and water depth, within the 239 conditions evaluated. For the UV/H 2 O 2 tests (Fig. 6b)

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In ANOVA (Table SM3), it appears that, in the UV-only system, the mineralization was not significant 248 (F calc <F tab ) and did not present a good correlation of the data (Fig. SM3), thus it was not possible to obtain an 249 equation capable of predicting the removal of TOC. However, in the UV/H 2 O2 system, ANOVA (Table SM4) 250 confirms the reliability of the results (Fig. SM4)

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The experimental results for PNF degradation obtained in the treatments with UV-only and UV/H 2 O 2 289 were adjusted to the first order, pseudo-first order and second order models. In Fig. 8, it is possible to observe that 290 the mathematical models evaluated showed good adjustments to the experimental data. In Table 3