TOC Abatement Research Articles

Synthesis by sol–gel of WO3/TiO2 for solar photocatalytic degradation of malathion pesticide

In this study, TiO2 modified with WO3 (2wt.%) was prepared by the sol–gel method, and its photocatalytic activity (PCA) under solar irradiation was evaluated using malathion as the model contaminant. The catalyst was synthesized using tetra butyl orthotitanate (TBT) and ammonium p-tungstate (ApT) as precursors. For comparison, bare TiO2 was also prepared by the sol–gel process. The resulting photocatalysts were characterized by XRD, BET, DRUV–vis, FE-SEM, TEM and STEM. The synthesized TiO2 materials exhibited a crystalline anatase phase with an average particle size of 20nm. Results of malathion degradation using solar light, indicated that 2%WO3/TiO2 showed better catalytic performance than sol–gel TiO2, achieving a complete degradation after 2h, while TOC abatement was 63% after 5h. These results suggest that 2%WO3/TiO2 catalyst is a promising material for solar photocatalytic treatment of water contaminated by pesticides.

Advanced oxidation of the commercial nonionic surfactant octylphenol polyethoxylate Triton™ X-45 by the persulfate/UV-C process: effect of operating parameters and kinetic evaluation.

This study explored the potential use of a sulfate radical (SO·−4)-based photochemical oxidation process to treat the commercial nonionic surfactant octylphenol polyethoxylate (OPPE) Triton™ X-45. For this purpose, the effect of initial S2O2−8 (0–5.0 mM) and OPPE (10–100 mg/L) concentrations on OPPE and its organic carbon content (TOC) removal were investigated at an initial reaction pH of 6.5. Results indicated that very fast OPPE degradation (100%) accompanied with high TOC abatement rates (90%) could be achieved for 10 and 20 mg/L aqueous OPPE at elevated S2O2−8 concentrations (≥2.5 mM). S2O2−8/UV-C treatment was still capable of complete OPPE removal up to an initial concentration of 40 mg/L in the presence of 2.5 mM S2O2−8. On the other hand, TOC removal efficiencies dropped down to only 40% under the same reaction conditions. S2O2−8/UV-C oxidation of OPPE was also compared with the relatively well-known and established H2O2/UV-C oxidation process. Treatment results showed that the performance of S2O2−8/UV-C was comparable to that of H2O2/UV-C oxidation for the degradation and mineralization of OPPE. In order to elucidate the relative reactivity and selectivity of SO·−4 and HO·, bimolecular reaction rate coefficients of OPPE with SO·−4 and HO· were determined by employing competition kinetics with aqueous phenol (47 μM) selected as the reference compound. The pseudo-first-order abatement rate coefficient obtained for OPPE during S2O2−8/UV-C oxidation (0.044 min−1) was found to be significantly lower than that calculated for phenol (0.397 min−1). In the case of H2O2/UV-C oxidation however, similar pseudo-first-order abatement rate coefficients were obtained for both OPPE (0.087 min−1) and phenol (0.140 min−1). From the kinetic study, second-order reaction rate coefficients for OPPE with SO·−4 and HO· were determined as 9.8 × 108 M−1 s−1 and 4.1 × 109 M−1 s−1, respectively. The kinetic study also revealed that the selectivity of SO·−4 was found to be significantly higher than that of HO·.

Electrochemical and Photochemical Oxidation of Cationic Dyes: A Comparative Study

This study reports on comparative performance of electro-Fenton and photo-Fenton processes in the mineralization of three cationic dyes: BB41, BR46 and BY28. Primary objective was to determine the optimal conditions for both processes. It has been shown that the mineralization rate by electro-Fenton process depends on operating parameters such as applied current density, catalyst con- centration, pH, etc. It was also observed that dyes degradation by hydroxyl radicals follows pseudo first-order reaction kinetics. Under the optimal operating conditions ((Fe 3+ ) = 0.2 mM, j = 3 mA cm -2 , and pH = 3), electro-Fenton process leads to an almost mineraliza- tion of dyes solutions reaching 93, 86 and 77% of TOC abatement for BB41, BR46 and BY28 respectively. The dye mineralization rate during photo-Fenton (UV/Fe 3+ /H2O 2) process is a function of reagent doses, and their concentration ratio R = (H2O2)/(Fe 3+ ). Thus, mineralization rates obtained are around 95, 93 and 85% for BB41, BR46 and BY28 respectively for a treatment time of 5 h with a ratio R = 10 and (Fe 3+ ) = 0.2 mM. The mineralization of a mixture of the three cationic dyes was also studied in a second step. Results showed that both photo-Fenton and electro-Fenton processes are able to reach almost complete mineralization rates. Finally the electro-Fenton process is considered the more efficient and interesting technique due to its environmentally friendly character with low energy consump- tion and no use of chemical reagents.

Synthesis of stable Cu-supported pillared clays for wet tyrosol oxidation with H2O2

In the present paper the synthesis of stable Cu-containing pillared clays catalysts (Cu-PILCs) is described. These catalysts were prepared by the solid-state reaction of Al-pillared clay with copper nitrate. The resultant materials were then treated with an oxalic acid solution in order to improve the dispersion of metal species on the alumina pillars. Characterization studies were performed by use of X-ray diffraction, nitrogen adsorption at 77K, chemical analysis, temperature-programmed reduction (H2-TPR) and transmission electron microscopy (TEM). The texture of the copper catalysts showed a high specific surface area and microporosity (197m2g−1 and 0.081cm3g−1 respectively for the catalyst Cu5.6Al-PILC), with high loading of copper (up to 4.72Cuwt%). TPRprofiles of catalysts show the presence of isolated copper species with high interaction with the alumina pillars.The properties of copper-based catalysts have been studied in the wet hydrogen peroxide oxidation of an aqueous solution of tyrosol, a molecule which constitutes more than half of the light fraction of the olive mill wastewater. The reaction was conducted in batch and flow reactors. Performance of catalysts remained quite excellent; total removal of tyrosol with high TOC abatement (around 65%) was obtained after 2h reaction. Furthermore, the Cu5.6Al-PILC(t) catalyst showed very high stability and performance in the flow reactor: 90% of tyrosol conversion and 78% of TOC removal are obtained in 192h on stream, without the detection of any change in the activity.

Effect of modification of textile wastewater composition on electrocoagulation efficiency

This paper deals with the efficiency of electrocoagulation (EC) for the abatement of COD, TOC, absorbance (i.e. color) and turbidity from a real textile wastewater, a pure red dye solution (disperse dyes 2-naphthoic acid and 2-naphthol) and a solution combining the two above fluids. The treatment of the dyestuff solution is satisfactory with high levels of color and organic pollution abatement. The treatment of the industrial waste is less efficient. Treatment of the solution combining the two above fluids allows to investigate whether the removal of several polluting matters by electrocoagulation could be considered as the superimposition of the various treatments of single-species effluents, in sort of additivity principle, as presented in an original model for the treatment of two-pollutant waste. Turbidity and TOC were shown to be additive variables in the treatment of the dye solution and the industrial textile waste: electrocoagulation seems to proceed with no interaction between the two types of matter to be removed, namely the dye stuff, and the lot of pollutants contained in the industrial waste.

Application of the UV-C photo-assisted peroxymonosulfate oxidation for the mineralization of dimethyl phthalate in aqueous solutions

In this study, the degradation of dimethyl phthalate (DMP), taken as model compound for phthalate esters, by the photo-assisted peroxymonosulfate (PMS) process was investigated. The high oxidation potential of hydroxyl and sulfate radicals generated by the activation of PMS under UV-C light irradiation was used to completely oxidize aqueous DMP solutions. Experiments were conducted at varying initial pH values (3.0, 6.0, and 9.0) and PMS concentrations (0-60 mM) to evaluate the effect of different reaction conditions on DMP treatment performance with the PMS/UV-C process. It was observed that lowering the initial reaction pH slightly improved the degradation rate of DMP. On the contrary, TOC abatements were slightly enhanced with increasing initial reaction pH. An adequate (optimum) PMS concentration of 40 mM resulted in the fastest and highest DMP degradation rates and efficiencies, respectively. At an initial concentration of 100 mg L(-1), more than 95% DMP removal was obtained after only 20 min under PMS/UV-C treatment conditions. For the proposed adequate PMS concentration (40 mM) the lowest electrical energy per order (EE/O) value was calculated as 2.9 kW h m(-3) order(-1).

Performance of the photo-Fenton process in the degradation of a model azo dye mixture

The degradation of a model mixture composed of Acid Yellow 36 (AY36) and Methyl Orange (MO) azo dyes was performed using the photo-Fenton process (PFP). The performance of this process conducted under artificial UV light (365 nm) was compared with the Fenton reaction. Some important operating parameters that affect the degradation of azo dyes, such as initial Fe(2+) and H(2)O(2) concentrations and the presence or absence of chloride ions, were investigated. Decolorisation of the dye mixture sample was achieved in 70 min with the photo-Fenton reaction, while the complete mineralization evaluated by TOC abatement was completed in 180 min. These results provide important knowledge for the treatment of wastewater containing azo dye mixtures by Fenton and photo-Fenton oxidation processes.

Development of experimental design models to predict Photo-Fenton oxidation of a commercially important naphthalene sulfonate and its organic carbon content

In the present study, Photo-Fenton oxidation of the commercially important K-acid (2-naphthylamine-3,6,8-trisulfonic acid) was optimized and modeled by employing response surface methodology and central composite design. The experimental design tool was used to assess the influence of treatment time ( t r), initial COD of aqueous K-acid solutions (COD o) as well as H 2O 2 and Fe 2+ concentrations on K-acid, COD and TOC removal efficiencies. According to the established second-order polynomial regression models, K-acid removal efficiency was affected by the process variables in the following decreasing order; t r > COD o (negative impact) > Fe 2+ > H 2O 2, while the effect on COD and TOC removals was COD o (negative impact) > H 2O 2 > t r > Fe 2+. Analysis of variance indicated that the experimental design models obtained for the Photo-Fenton oxidation of aqueous K-acid and its organic carbon content (expressed as COD and TOC) were statistically significant and satisfactorily described the treatment process for the entire Photo-Fenton treatment period (up to 125 min) as well as different treatment targets (partial and full oxidation) and initial COD values (150–750 mg/L). Complete K-acid removal accompanied with high COD (70–100%) and TOC (55–100%) abatements were achieved under relatively mild Photo-Fenton treatment conditions.

Catalytic Wet-Air Oxidation of p-Cresol on Ag/Al2O3−ZrO2 Catalysts

Catalytic wet-air oxidation of p-cresol was carried out on Ag/Al2O3−ZrO2 catalysts at 1, 5, 10, and 20 wt % of ZrO2 in a reactor-type batch and 160 °C and 15 bar of oxygen. Al2O3−ZrO2 supports were prepared by the simultaneous hydrolysis of the boehmite and zirconium alkoxide. Ag/Al2O3−ZrO2 catalysts prepared by deposition−precipitation showed higher surface area (202−216 m2/g) and lower Lewis acids sites than the Ag/Al2O3 (161 m2/g) and Ag/ZrO2 (25 m2/g) reference catalysts. FTIR-CO adsorption showed a shift to lower frequencies on Ag/Al2O3−ZrO2 catalyst indicating electron-rich metallic particles. The p-cresol conversion, TOC abatement, and CO2 selectivity were improved when Ag was supported on Al2O3−ZrO2 mixed oxides. A modification of the surface properties of Ag on the Ag/Al2O3−ZrO2 catalysts due to a metal−support interaction leading to a faster oxidation of the adsorbed reactant species is proposed.

Mechanistic and kinetic insights into the wet air oxidation of phenol with oxygen (CWAO) by homogeneous and heterogeneous transition-metal catalysts

The activity–selectivity pattern of homogeneous (Cu2+, Fe3+, Mn2+) and ceria-supported (CuCeOx, MnCeOx) transition-metal catalysts in the wet air oxidation of phenol (CWAO) has been probed using a stirred batch reactor with continuous oxygen feeding (T, 150°C; PO2, 0.9Mpa). Both non-catalytic and catalytic homogeneous wet air oxidations proceed via an unselective autocatalytic free-radical path leading mostly to refractory C1–C2 acids, while a Langmuir–Hinshelwood (L–H) mechanism accounts for the superior CWAO performance of the MnCeOx system. A thorough kinetic analysis of the studied systems on the basis of homogeneous autocatalytic free-radical and heterogeneous surface L–H reaction paths has been addressed. The kinetic constants of the various reaction steps show that the MnCeOx system prompts a fast adsorption of phenol with the consequent abatement of TOC, though a slow oxidation rate determines the buildup of carbonaceous deposits on the catalyst surface. Lower oxidation strength and extensive leaching definitively argue against Cu-based catalysts for the CWAO process.

Electrochemical Treatment of synthetic and Actual Dyeing Wastewaters Using BDD Anodes

In this work, the treatment of synthetic wastewaters containing methylene blue (MB) and rhodamine B (RB) and actual textile wastewaters (ATW) using boron doped diamond (BDD) anodic oxidation was investigated. Voltammetric study has shown that both MB and RB can be oxidized directly at the anode surface in the potential region where the electrolyte salt is stable. Galvanostatic electrolyses of synthetic and actual industrial wastewaters have led to total abatement of COD and TOC at different operating conditions (electrolyte salt and initial pollutant concentration and current density) and the efficiency of the electrochemical process was governed only by mass-transfer limitations. The nature of the supporting electrolyte has a great influence on the rate and the efficiency of the electrochemical oxidation of dyes. The treatment in the presence of NaCl appears to be more efficient in the COD removal, while in the presence of Na2SO4 improves the TOC removal. From the experimental results it seems that the primary mechanisms in the oxidation of dyes are the mediated electro-oxidation by hydroxyl radicals and other oxidants electro-generated from supporting electrolyte oxidation.

An optimization and modeling approach for H2O2/UV‐C oxidation of a commercial non‐ionic textile surfactant using central composite design

AbstractBACKGROUND: Industrial surfactants are biologically complex organics that are difficult to degrade and may cause ecotoxicological risks in the environment. Until now, many scientific reports have been devoted to the effective treatment of surfactants employing advanced oxidation processes, but there is no available experimental study dealing with the optimization and statistical design of surfactant oxidation with the well‐established H2O2/UV‐C process.RESULTS: Considering the major factors influencing H2O2/UV‐C performance as well as their interactions, the reaction conditions required for the complete oxidation of a commercial non‐ionic textile surfactant, an alkyl ethoxylate, were modeled and optimized using central composite design‐response surface methodology (CCD‐RSM). Experimental results revealed that for an aqueous non‐ionic surfactant solution at an initial chemical oxygen demand (COD) of 450 mg L−1, the most appropriate H2O2/UV‐C treatment conditions to achieve full mineralization at an initial pH of 10.5 were 47 mmol L−1 H2O2 and a reaction time of 86 min (corresponding to a UV dose of 30 kWh m−3).CONCLUSION: CCD allowed the development of empirical polynomial equations (quadratic models) that successfully predicted COD and TOC removal efficiencies under all experimental conditions employed in the present work. The process variable treatment time, followed by the initial COD content of the aqueous surfactant solution were found to be the main parameters affecting treatment performance, whereas the initial H2O2 concentration had the least influence on advanced oxidation efficiencies. The H2O2 concentration and surfactant COD were found to be more important for TOC abatement compared with COD abatement. Copyright © 2009 Society of Chemical Industry

Semicontinuous Fenton oxidation of phenol in aqueous solution. A kinetic study

This work investigates the Fenton oxidation of phenol in a semicontinuous reactor where the overall amount of H 2O 2 is distributed as a continuous feed upon the reaction time. The experiments were carried out at 25 °C and atmospheric pressure, with 100 mg/L initial phenol concentration and iron dosages from 1 to 100 mg/L. H 2O 2 aqueous solution was continuously fed during 4 h reaction time up to an overall dose varying within the range of 500–5000 mg/L. The results in terms of evolution of phenol, H 2O 2 and intermediates, as well as TOC abatement were compared with those obtained in conventional batch operation. It was found that the oxidation rates for phenol and intermediates were lower when adding the H 2O 2 continuously. However, a higher abatement of TOC was reached at the end of the 4-h reaction time, in spite of a similar overall H 2O 2 consumption. This is the result of a more efficient OH generation throughout the semicontinuous process, favouring the reaction with the organic species and reducing the occurrence of competitive scavenging reactions involving Fe 2+, H 2O 2 and OH. Two kinetic models were proposed, one for describing the evolution of phenol, aromatics and H 2O 2 and the other for TOC. The influence of the operating conditions on the kinetic constants was also studied, looking for the optimal conditions in terms of both, environmental and economic points of view.

Treatment of phthalic acid esters by electrocoagulation with stainless steel electrodes using dimethyl phthalate as a model compound

In this study, treatment of phthalates by electrocoagulation employing stainless steel electrodes was investigated using dimethyl phthalate (DMP) as a model compound. DMP was completely destructed within 30 min up to the high initial concentration of 100 mg/L while total mineralization was also obtained within a couple of hours. The applied current density of 22.5 mA/cm 2 and electrolyte (NaCl) concentrations varying between 1000 and 1500 mg/L as chloride resulted in the highest treatment performance. The initial solution pH (2–6) had practically no effect on the process efficiency. Desorption experiments and the reaction rates obtained for DMP, COD and TOC abatements appeared to be a strong evidence of an oxidative removal mechanism. DMP removal fitted first order kinetics. COD and TOC removals began after the total DMP removal and also fitted first order kinetics. Activated sludge inhibition experiments revealed that toxicity could be significantly reduced by electrocoagulation application.

LaFeO3 Perovskite as New and Performant Catalyst for the Wet Peroxide Oxidation of Organic Pollutants in Ambient Conditions

The purpose of the present study was to evaluate the ability of LaFeO3 perovskites prepared using the “self-combustion method” to behave as efficient and stable catalysts in phenol oxidation using H2O2 in ambient conditions. Depending on the synthesis conditions, strong differences in the structural, textural and reducibility characteristics of the perovskites, as well as in phenol conversion and TOC abatement level were observed. High TOC abatement (76%) and very low iron leaching (0.27 wt%) were obtained at 40 °C in the presence of LaFeO3 nanoparticles exhibiting the lowest crystal domain size.

Adsorption and oxidation of PCP on the surface of magnetite: Kinetic experiments and spectroscopic investigations

The oxidation of pentachlorophenol (PCP) on the surface of magnetite used as heterogeneous catalyst has been investigated under various experimental conditions (initial substrate concentration, H2O2 dose, solid loading and temperature) at neutral pH and correlated with the adsorption behavior. The surface reactivity of magnetite was evaluated by conducting the kinetic study of both H2O2 decomposition and PCP oxidation experiments. The occurrence of the optimum values of H2O2 and magnetite concentrations for the effective degradation of PCP could be explained by the scavenging reactions with H2O2 or iron oxide surface. The surface interactions with PCP in the absence and the presence of oxidant can be well described by Langmuir and Langmuir–Hinshelwood models, respectively. All batch experiments indicate that Fenton-like oxidation of PCP was controlled by surface mechanism reaction and the species compete with each other for adsorption on a fixed number of surface active sites. The apparent degradation rate was dominated by the rate of intrinsic chemical reactions on the oxide surface rather than the rate of mass transfer. Raman analysis suggested that the sorbed PCP was removed form magnetite surface at the first stage of oxidation reaction. The mineralization determined by TOC abatement was completed after 7 d, while total dechlorination was achieved at 4 d treatment time. The first reaction of PCP oxidation should be the dechlorination since 90% of chloride was formed at the first 30h corresponding to the total disappearance of parent compound. All X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Mössbauer spectroscopy and chemical analyses showed that the magnetite catalyst exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle.

Ruthenium catalysts supported on TiO2 prepared by sol–gel way for p-hydroxybenzoic acid wet air oxidation

The wet air oxidation of p-hydroxybenzoic acid, chosen as a model compound of olive mills wastewaters was carried out at 140 °C and 50 bar air over Ru catalysts supported on TiO2 prepared by sol–gel method. These catalysts were characterized by means of N2 adsorption–desorption, XRD and TEM. Optimization of the catalytic performances was obtained by studying some parameters such as the catalyst preparation method, the solvent evacuation way, the nature of the hydrolysis agent, the influence of the ruthenium salt used as the metal precursor (Ru(NO)(NO3)3 or Ru(acac)3) and the catalyst pretreatment. The pre-calcination of the catalyst precursor at 300 °C under oxygen, before the reduction step under hydrogen, was detrimental to the activity. The results showed that the use of nitric acid as hydrolysis agent, drying under supercritical conditions and the use of Ru(NO)(NO3)3 leads to the more efficient catalyst with high TOC abatement.

UV-C light-enhanced photo-Fenton oxidation of methyl parathion

The photodegradation of aqueous solutions containing 0.2 mM methyl parathion has been studied through the optimization of the [H2O2]/[Fe3+] ratio in a Fe3+/H2O2/UV-C flow system of 1.3 L capacity. The decay kinetics and TOC abatement have been analyzed for the experiments performed at pH 3.0 and room temperature. All experiments lead to the total methyl parathion destruction after a few minutes, following a pseudo-first-order decay kinetics. Total mineralization can be reached after 120 min at the optimum ratio found, due to the synergistic effect of the very oxidizing hydroxyl radical (·OH) produced via the Fenton reagent and the effective photodecarboxylation at 253.7 nm.

Copper-supported pillared clay catalysts for the wet hydrogen peroxide catalytic oxidation of model pollutant tyrosol

Abstract The catalytic wet hydrogen peroxide oxidation of tyrosol, a major compound of the polyphenolic fraction present in olive oil mill wastewaters, was studied in batch and continuous reactors using copper-supported pillared clay catalysts under mild conditions. The catalysts were prepared by the solid-state reaction of Al-pillared clay synthesized with copper nitrate. The resultant materials were then calcined at 300 °C for 3 h under helium or oxygen. The catalytic activity of Cu-supported pillared clays was found to depend on the calcination method. The effects of several operating conditions were also studied. Our experimental results indicate that, under mild conditions and a stoichiometric amount of oxidant, the calcined material under helium (CuNHe catalyst) showed higher activity and stability (TOC abatement of roughly 80% and total elimination of tyrosol after 1 h reaction, without significant leaching of copper ions) than the calcined material under oxygen (CuNOxy). To better understand the catalytic behaviour of copper-supported pillared clay solids, fresh and used catalysts were characterized by X-ray diffraction, nitrogen adsorption, chemical analysis, temperature-programmed reduction (TPR), UV–visible diffuse reflectance spectroscopy, and transmission electron microscopy (TEM).

Ozonation of Two Commercially Important Biocidal Finishing Agents

Ozonation of 2 commercially important textile biocidal finishing agents (called BI and BII herein) in aqueous solution was studied in a semi-batch bubble column reactor at different ozone feed rates (500, 750, and 900 mg/h) and pH (pH=7 and 12). Ozonation efficiency and kinetics were assessed in terms of COD, TOC and UV absorbance at 280 nm (UV280) and 254 nm (UV254), representing the aromaticity and unsaturated moieties of the studied textile biocides, respectively. Due to its chlorinated aromatic content, the fate of Adsorbable Organic Halogens (AOX) of BI was also followed during the ozonation experiments. At alkaline pH, appreciably higher COD and TOC removals were achieved, speaking for a free radical (•OH) dominated degradation pathway for both tested biocides. AOX, UV280 and TOC abatement rates obtained for BI ozonation at optimized reaction conditions indicated that the degradation of BI followed a sequential path of dechlorination, dearomatization, oxidation and mineralization, respectively.