Degradation of sulphamethazine by means of an improved photo-Fenton process involving a hydrogen peroxide systematic dosage

Modelling of the photo-Fenton process with flexible hydrogen peroxide dosage: Sensitivity analysis and experimental validation

The supply of hydrogen peroxide (H₂O₂) controlling the amount of highly oxidant hydroxyl radicals is the most critical operational issue for the photo-Fenton process. Accordingly, this study addresses the development of a model for photo-Fenton processes including a flexible H₂O₂ supply given as a function of time. The model is aimed at its future exploitation in treatment optimization and the determination of the optimal profile for H₂O₂ supply. The work has adopted a photo Fenton model previously reported that includes the inlet flow (fed-batch) and describes the system dynamics under a flexible dosage. Thus, model global sensitivity analysis (GSA) and parameter estimation were performed using Simulink® to examine the behavior of the model under flexible H₂O₂ dosage. GSA was carried out using partial rank correlation methods and the Latin hypercube sampling to assess to which extent variations of the model parameters affect each measured response (H₂O₂, total organic carbon, TOC, and dissolved oxygen, O₂ -the experimentally available information). Hence, the model is discussed in regard of its hypothesis and chances for reducing its complexity. This resulted in the rejection of two reactions of the initial model. Next, a set of 12 kinetic, stoichiometric and operative parameters was estimated through the fitting of H₂O₂, TOC, and O₂ profiles. Discussion on model fitting includes computational issues, the role of initial values for the estimation process, the goodness of fit criteria, and the sampling method. The model was fit to experimental data with assorted H₂O₂ supply profiles and validated, and Root Mean Square Error (RMSE) below 0.009 mM, 0.42 mM, and 0.127 mM were obtained for TOC, H₂O₂ and O₂, respectively. Therefore, this work contributes a practical model aimed at providing model-based optimization for the H₂O₂ dosage profile of the photo-Fenton process.

Feasibility of resource utilization of the refractory evaporation concentrate of gas field wastewater exhibiting high salinity: Application of UV/Fenton, desulfurization, distillation and crystallization process after pre-treatment

The evaporation concentrate of gas field wastewater (EC-GFW) is a new type of refractory actual wastewater produced by the three-effect evaporation of gas field wastewater, exhibiting extremely high salinity and complex organic components. This study proposed a set of processes consisting of AOPs, precipitation, distillation, and crystallization for the systematic treatment of EC-GFW. In this paper, the optimal conditions for the processes after pre-treatment were investigated. The optimal operating parameters of UV/Fenton process were determined to be 180 min of reaction time, 4 of initial pH, 0.6 mol/L of H₂O₂ dosage, 10:1 of n(H₂O₂): n(Fe²⁺) value, and 30 W of UV power. Fenton's reagent was added in two steps (0 min and 90 min) for effective utilization. The results showed that the TOC (Total organic carbon) removal efficiency during the two-stage oxidation reached 93% with TOC in the effluent of 132 mg/L. Then, 82.3% of sulfate ions were removed by the desulfurization process using 50 g/L of CaCl₂ within 10 min at a pH of 5 before distillation. It was found that the TOC in the influent of distillation played a decisive role in the quality of the effluent and purity of the crystalline salt, which was expected to be controlled lower than 132 mg/L. The final condensate could utilize to reuse, 99% of main pollutants of which have been removed, reducing the pressure of water supply on site. Simultaneously, the industrial-grade NaCl with extensive application prospect can be recovered. The harmless disposal and resource utilization of EC-GFW was achieved on a laboratory scale, providing the data support and theoretical guidance for treating EC-GFW at gas field project site.

Sulfaquinoxaline Oxidation and Toxicity Reduction by Photo-Fenton Process

Sulfaquinoxaline (SQX) has been detected in environmental water samples, where its side effects are still unknown. To the best of our knowledge, its oxidation by Fenton and photo-Fenton processes has not been previously reported. In this study, SQX oxidation, mineralization, and toxicity (Escherichia coli and Staphylococcus aureus bacteria) were evaluated at two different setups: laboratory bench (2 L) and pilot plant (15 L). The experimental design was used to assess the influence of the presence or absence of radiation source, as well as different H2O2 concentrations (94.1 to 261.9 mg L-1). The experimental conditions of both setups were: SQX = 25 mg L-1, Fe(II) = 10 mg L-1, pH 2.8 ± 0.1. Fenton and photo-Fenton were suitable for SQX oxidation and experiments resulted in higher SQX mineralization than reported in the literature. For both setups, the best process was the photo-Fenton (178.0 mg L-1 H2O2), for which over 90% of SQX was removed, over 50% mineralization, and bacterial growth inhibition less than 13%. In both set-ups, the presence or absence of radiation was equally important for sulfaquinoxaline oxidation; however, the degradation rates at the pilot plant were between two to four times higher than the obtained at the laboratory bench.

Assessment of the UV/Cl2 advanced oxidation process for the degradation of the emerging contaminants amitriptyline hydrochloride, methyl salicylate and 2-phenoxyethanol in water systems

Three emerging contaminants (amitriptyline hydrochloride (AH), methyl salicylate (MS) and 2-phenoxyethanol (PE)) frequently found in wastewaters were selected to be individually degraded in ultra-pure water by the advanced oxidation process (AOP) constituted by the combination of UV radiation and chlorine. The influence of pH, initial chlorine concentration and nature of the contaminants was firstly explored. The trend for the reactivity of the selected compounds was deduced: AH > MS > PE. A later kinetic study was carried out focused on the evaluation of the first-order rate constants and the determination of the partial contribution to the global reaction of the direct photochemical pathway and the radical pathway. In a second stage, the simultaneous oxidation of mixtures of the selected contaminants in several types of water was also performed by the same combination UV/Cl₂. The efficiency of this combined system UV/Cl₂ was compared to other oxidants such as the UV/[Formula: see text] and UV/H₂O₂ AOPs, and the influence of the operating variables was discussed. Results confirmed that the UV/Cl₂ system provides higher elimination efficiencies among the AOPs tested. The presence of dissolved organic matter and bicarbonate ions in the water matrix caused a decrease in the treatment efficiency.

Degradation of antidepressant drug fluoxetine in aqueous media by ozone/H2O2 system: process optimization using central composite design

The main objective of this work is the modelling and optimization of antidepressant drug fluoxetine degradation in aqueous solution by ozone/H2O2 process using central composite design. The operational parameters were ozone concentration, initial hydrogen peroxide concentration, reaction time and initial fluoxetine concentration. A good agreement between the predicted values of fluoxetine removal and experimental results were observed (R2=0.976 and Adj-R2=0.955). Pareto analysis indicated that all selected factors and some interactions were effective on the removal efficiency. It was found that the reaction time is the most effective parameter in the ozone/H2O2 process. The maximum removal efficiency (86.14%) was achieved at ozone concentration of 30 mg L(-1), initial H2O2 concentration of 0.02 mM, reaction time of 20 min and initial fluoxetine concentration of 50 mg L(-1) as the optimum conditions.