Degradation of 4-chloro-2-methylphenol in aqueous solution by electro-Fenton and photoelectro-Fenton processes

Degradation of 4-chloro-2-methylphenol (PCOC), a refractory toxic chemical emitted to the environment from the industrial production of phenoxy herbicides was studied in aqueous solution. Electro-Fenton and photoelectro-Fenton processes were used as the degradation methods. H₂O₂, produced by the reduction of oxygen at carbon cathode reacted with dissolved metal ions to form hydroxyl radicals, which in turn reacted with PCOC sequentially to degrade the aromatic ring. The effects of using different [Fe²⁺]/[PCOC]₀ and the effect of replacing Fe²⁺ by Mn²⁺ ion have been examined. It was found that degradation rate was increased with increasing [Fe²⁺]/[PCOC]₀ ratio from 2 to 4. However, the total charge utilized during the treatment was also increased. The efficiency of PCOC degradation was observed to be higher when Mn²⁺ was used as the catalyst. The mineralization of aqueous solutions of PCOC, withdrawn from the reactor at certain time interval, has been followed by total organic carbon (TOC) decay and dechlorination. A fast and complete degradation of the aromatic ring was achieved in photoelectro-Fenton system. 41.7% TOC decay and complete dechlorination were observed by consuming only 141.4 C electrical charge during a 300 min photoelectron-Fenton treatment. In the case of electro-Fenton system, 280.7 C electrical charge was consumed during 450 min of electrolysis to attain a similar degradation of PCOC. 14.9% TOC removal and 89.3% dechlorination have been obtained in this system under the applied conditions.     

Reduction of nitrite by sulfamic acid and sodium azide from aqueous solutions treated by gliding arc discharge

Nitrous and nitric acids form in aqueous solutions exposed to a gliding arc discharge burning in humid air. The anions interfere when the concentration of particular solutes such as pollutants must be determined. In particular they falsify the COD measurements and spectral investigations and thus the efficiency of the plasma treatment in pollutant abatement. The nitrite anions must be thus removed, which require specific reagents. The influence of parameters such as solution pH and [reducers]/[NO₂⁻] ratio on the reduction reaction was evaluated. The reduction of nitrite into N₂ either by sulfamic acid or sodium azide is a first-order pH-dependant reaction with regard to nitrite and reducers (k₁ = 2.93 × 10⁻¹ m³ kmol⁻¹ s⁻¹; k₂ = 6.21 × 10⁻¹ m³ kmol⁻¹ s⁻¹, respectively). Sodium azide is thus more reactive than sulfamic acid.     

Treatment of a mixture of three pesticides by photo- and electro-Fenton processes

In the present work, a comparative study of a mixture of three pesticides (chlortoluron, carbofuran and bentazon) has been investigated by advanced oxidation processes such as photo-Fenton and electro-Fenton. These processes are based on the in situ production of hydroxyl radical, a highly strong oxidant, which allows the degradation of organic pollutants until their mineralization into CO₂ and H₂O. For the photo-Fenton process, the effect of key parameters such as initial catalyst (Fe³⁺) concentration and hydrogen peroxide (H₂O₂) dosage were studied. Under optimal operating conditions, the evolution of total organic carbon (TOC) has been investigated for the two processes. Obtained results showed that more than 90% of TOC removal was obtained after only 2 h of photo-Fenton treatment whereas the electro-Fenton process needed 8 h of treatment. Nevertheless, the comparison of cost treatment shows that the photo-Fenton process is more expensive than electro-Fenton. The evolution of pesticide's concentration during treatment was determined by high performance liquid chromatography (HPLC). Inorganic ions released such as chloride, nitrate, sulphate and ammonium ions are identified and their kinetic evolution was measured by ion chromatographic analyses.     

Influence of operating parameters on photocatalytic degradation of phenol in UV/TiO2 process

The use of hydrogen peroxide (H₂O₂) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO₂ powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H₂O₂/UV, TiO₂/UV, and H₂O₂/TiO₂/UV processes in a batch reactor with high-pressure mercury lamp irradiation. The effects of operating parameters such as catalyst dosage, light intensity, pH of the solution, the initial phenol, and H₂O₂ concentrations on photodegradation process were examined. It was shown that photodegradation using H₂O₂/TiO₂/UV process was much more effective than using either H₂O₂/UV or TiO₂/UV process. The effect of the initial phenol concentration on TOC removal was also studied, demonstrating that more than 8 h was required to completely mineralize phenol into water and carbon dioxide. For all the four oxidation processes studied, photodegradation followed the first-order kinetics. The apparent rate constants with 400-W UV ranged from 5.0 × 10⁻⁴ min⁻¹ by direct photolysis to 1.4 × 10⁻² min⁻¹ using H₂O₂/TiO₂/UV process. The role of H₂O₂ on such enhanced photodegradation of phenol in aqueous solution was finally discussed.     

Microwave-enhanced catalytic degradation of phenol over nickel oxide

A mix-valenced nickel oxide, NiO_x, was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Further, pure nickel oxide was obtained from the NiO_x by calcination at 300, 400 and 500 °C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), nitrogen adsorption at −196 °C and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of phenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhance catalytic degradation (MECD) of phenol have been investigated. The results indicated that the relative activity affected significantly with the oxidation state of nickel, surface area and surface acidity of nickel oxide, i.e., NiO_x (>+2 and S_BET = 201 m² g⁻¹)  C300 (+2 and S_BET = 104 m² g⁻¹) > C400 (+2 and S_BET = 52 m² g⁻¹) > C500 (+2 and S_BET = 27 m² g⁻¹). The introduction of microwave irradiation could greatly shorten the time of phenol degradation.     

Sorption kinetics of ammonia and ammonium ions on gel and macroporous sulphonic acid cation exchangers

Diffusion of ammonia and ammonium ions in sulphonic acid cation exchangers (gel Purolite SGC 100 × 10 MBH and macroporous Purolite C 160 MBH) from the solutions, representing the composition of “caustic condensate” (waste of nitrogen fertilizers production) is affected by pH of initial solution and structure of the matrix of cation exchanger. In gel matrix the effective intraparticle diffusivity (D_ef) depends greatly on the solution pH because of shrinkage in alkaline and swelling in acidic medium: on decreasing the initial concentration of ammonia from 0.214 to 0.003 and increasing that of ammonium nitrate from 0 to 0.214 mol l⁻¹ instead, the effect of ion exchange leads to a decrease in pH, resulting in swelling and increase in D_ef from 0.1 to 0.34 × 10⁻¹⁰ for gel Purolite SGC 100 × 10 MBH and variation of 0.18–0.11 × 10⁻¹⁰ m² s⁻¹ for macroporous Purolite C 160 MBH (resistant to shrinkage and swelling).

In Purolite C 160 MBH both macropore diffusivity (0.07–0.29 × 10⁻¹⁰ m² s⁻¹) and gel (solid phase) diffusivity (0.06–0.19 × 10⁻¹⁰ m² s⁻¹) are higher than micropore diffusivity (0.28–0.56 × 10⁻¹⁸ m² s⁻¹).

With respect to the effective intraparticle diffusivity, resistance to nitric acid, used for the regeneration, and high concentration of ammonium nitrate in eluate (up to 110 g l⁻¹), Purolite C 160 MBH has been installed for the conversion of ammonia and ammonium ions to ammonium nitrate reusable in the fertilizers production. This allows minimizing the economic loss and preventing the environmental contamination.     

Gliding arc plasma assisted photocatalytic degradation of anthraquinonic acid green 25 in solution with TiO2

Anthraquinonic acid green 25 (AG 25) removal was investigated by plasmachemistry using non-thermal gliding arc at atmospheric pressure. The gaseous species formed in the discharge, and especially OH radicals, induce strong oxidizing effects in the target solution. The removal of the dye was carried out in the absence and presence of TiO₂ as photocatalyst. The decolourization of AG 25 was followed by UV–vis spectrometry (at 643 nm), while the degradation was followed by COD measurements. The effects of operating variables such as initial concentration of AG 25 and catalyst concentration were investigated. Experiments were carried out to optimise the amount of TiO₂. The results showed that maximum degradation was attained for 2 g L⁻¹ TiO₂ concentration. At this optimum concentration, the dye (80 μM) was totally decolourized within 15 min of plasma-treatment time, and 93% removal of initial COD was attained after a 180-min plasma-treatment time. In the absence of catalyst, colour removal was 46% after 15 min, while COD abatement reached 84% after 180 min. The extent of degradation decreased with initial concentration and the time required for complete degradation increased. In all cases, the plasma-treated samples in the presence or absence of catalyst were found to follow pseudo-first order reaction kinetics. The TiO₂-mediated plasmachemical process showed potential application for the treatment of dye solutions, resulting in the mineralization of the dye confirmed by sulfate ion formation.     

Cloth catalysts for water denitrification: II. Removal of nitrates using Pd–Cu supported on glass fibers

The use of glass fibers in the form of woven cloth (GFC), as a new type of catalytic support, was studied for the reduction of aqueous nitrate solutions using a Pd/Cu–GFC catalyst. The activity (per gram Pd) and selectivity to nitrogen were found to be comparable with those found for Pd–Cu catalysts supported on the other carriers. The maximal initial removal activity was found for a catalyst with a Pd/(Pd+Cu) ratio of 0.81. The corresponding activity was 0.7 mmol min⁻¹ (g_Pd)⁻¹, and the selectivity was 97 mol% at 25°C and pH 6.5 for initial nitrate concentration of 100 mg l⁻¹. The selectivity to nitrogen declined at high conversions of nitrate and high pH.     

Reverse osmosis of diluted skim milk: Comparison of results obtained from vibratory and rotating disk modules

This paper investigates the reduction of ionic concentration and carbon oxygen demand (COD) in dairy process waters modelled by one volume of skim milk diluted with two volumes of water using shear-enhanced reverse osmosis. Initial COD and conductivity were, respectively, 36,000 mg O₂ L⁻¹ and 2000 μS cm⁻¹. We have compared the performances of a VSEP vibratory pilot and of a single rotating disk-stationary membrane module equipped with the same Desal AG membrane (Osmonics). Membrane shear rates were varied by changing the vibration frequency in the VSEP and the disk rotation speed or adding radial vanes in the other module. In all tests the permeate COD was reduced below 15 mg O₂ L⁻¹. Permeate fluxes reached a maximum of 180 L h⁻¹ m⁻² at a transmembrane pressure (TMP) of 4 MPa at initial concentration with the VSEP at its resonant frequency and with the disk equipped with 6 mm high vanes rotating at 2000 rpm. Permeate conductivity fell from 60 μS cm⁻¹ at 1 MPa to about 18 μS cm⁻¹ at 4 MPa. In concentration tests, corresponding permeate fluxes at the maximum volume reduction ratio reached (VRR = 8), were 55 L h⁻¹ m⁻² for the VSEP and 60 L h⁻¹ m⁻² for the rotating disk at a TMP of 4 MPa. Permeate conductivities increased exponentially with VRR from 18 to 210 μS cm⁻¹ for the rotating disk and to 250 μS cm⁻¹ for the VSEP. However the mean conductivity of collected permeate varied from 38 μS cm⁻¹at highest shear rate to 60 at lower shear rates. This study shows that these filtration systems permit to obtain reusable water from this high initial COD model effluent with one single reverse osmosis step.     

Degradation of Alizarin Red by electro-Fenton process using a graphite-felt cathode

The removal of the anthraquinone dye Alizarin Red S (AR) has been investigated by electro-Fenton process using a commercial graphite-felt to electrogenerate in situ hydrogen peroxide and regenerate ferrous ions as catalyst. The effect of operating conditions such as applied current, catalyst concentration, and initial dye content on AR degradation has been studied. AR decay kinetic, the evolution of its oxidation intermediates and the mineralization of the aqueous solutions were monitored during the electrolysis by UV–Vis analysis and TOC measurements. The experimental results showed that AR was completely removed by the reaction with OH radicals generated from electrochemically assisted Fenton's reaction, and the decay kinetic always follows a pseudo-first-order reaction. Applying a current of 300 mA and with catalyst concentration of 0.2 mM Fe²⁺, 95% of the initial TOC was removed in 210 min of electrolysis, meaning the almost complete mineralization of the organic content of the treated solution.     

Acridine yellow as solar photocatalyst for enhancing biodegradability and eliminating ferulic acid as model pollutant

The possibility of using acridine yellow G (AYG) as solar photocatalyst for wastewater treatment has been examined in this paper. A phenolic compound, namely ferulic acid, has been employed as target pollutant. The effect of pH, concentration of the substrate and photocatalyst has been investigated. Control of pH is critical in the process, as rate constants obtained at pH 3 (k = 0.020 min⁻¹) were one order of magnitude higher than in basic media (k = 0.002 min⁻¹ at pH 9), due to differences in the absorption spectrum in the UVA–vis region. Under acidic conditions, 80% removal of the substrate was achieved after 3 h irradiation, although TOC decrease was moderate (around 20%). Nevertheless important detoxification of the solution was measured, and the remaining organic matter showed an enhanced biodegradability. For this reason, a combination of AYG-driven solar photocatalysis with biological treatment seems a good approach to deal with these effluents. Experimental data are consistent with an electron transfer mechanism between the excited photocatalyst and the substrate: involvement of hydroxyl radicals can be ruled out, and photophysical measurements indicate a quenching of the fluorescence of AYG in the presence of ferulic acid. The rate constant for this process was obtained from the Stern–Volmer equation (k_q = 4.4 × 10⁹ M⁻¹ s⁻¹). Finally, based on the Rehm–Weller equation, a ΔG = −22.8 kcal/mol was calculated, indicating that the process is thermodynamically favourable.     

Selective permeation and separation of steam from water–methanol–hydrogen gas mixtures through mordenite membrane

Separation properties of a mordenite membrane for water–methanol–hydrogen mixtures were studied in the temperature range from 423 to 523 K under pressurized conditions. The mordenite membrane was prepared on the outer surface of a porous alumina tubular support by a secondary-growth method. It was found that water was selectively permeated through the membrane. The separation factor of water/hydrogen and water/methanol were 49–156 and 73–101, respectively. Even when only hydrogen was fed at 0.5 MPa, its permeance was as low as 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹ up to 493 K, possibly suggesting that water pre-adsorbed in the micropores of mordenite hindered the permeation of hydrogen. The hydrogen permeance dramatically increased to 6.5 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 503 K and reached to 1.4 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 523 K because of the formation of cracks in the membrane. However, the membrane was thermally stabilized in the presence of steam and/or methanol.     

Effects of oxygen concentration on the electrical properties of ZnO films

In this paper, electrical characteristics by various oxygen content in ZnO films were studied. To control the oxygen content of ZnO films, post-thermal annealing was performed in N₂ and air ambient, led to improve crystallinity and optical properties of ZnO films. The oxygen concentration was measured by Auger electron spectroscopy. The ZnO films having the deficiency of oxygen showed the electron concentrations between 10²¹ and mid 6 × 10¹⁷ cm⁻³ and resistivity at 10⁻³–10⁻¹ Ω cm. On the other hand, when the oxygen concentration of the ZnO films was up to the stoichiometry with Zn, the ZnO films showed low electron concentration at −10¹⁷ cm⁻³ and resistivity at 10 Ω cm.     

New synthesised pyridazine derivatives as effective inhibitors for the corrosion of pure iron in HCl medium

The inhibition of pure iron in 1 M HCl by new synthesised pyridazine compounds has been studied by weight loss, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements. The results obtained reveal that these compounds are efficient inhibitors. The inhibition efficiency increases with the increase of inhibitor concentration and reached 98% at 10⁻⁴ M for 5-benzyl-6-methyl pyridazine-3-thione. Potentiodynamic polarisation studies clearly reveal that the presence of pyridazines does not change the mechanism of hydrogen evolution and that they act essentially as cathodic inhibitors. The temperature effect on the corrosion behaviour of pure iron in 1 M HCl without and with the pyridazines at 10⁻⁴ M was studied in the temperature range from 298 to 353 K. EIS measurements show that the increase of the transfer resistance with the inhibitor concentration.     

Iodosulfuron degradation by TiO2 photocatalysis: Kinetic and reactional pathway investigations

The photocatalytic degradation of a sulfonylurea herbicide, iodosulfuron methyl ester (IOME), has been studied in TiO₂ aqueous suspensions under UV irradiation. The influence of various parameters such as initial concentration, TiO₂ concentration and light intensity on the kinetic process was investigated. Disappearance rate of iodosulfuron followed pseudo-first order kinetics. A special attention was devoted to the identification of intermediates, using a new analytical approach which consists of coupling HPLC–DAD (UV), HPLC–ESI-MS and HPLC–¹H NMR techniques after a SPE pre-concentration step. By combining UV, MS and NMR data, up to 20 degradation products were unambiguously identified. Furthermore, ¹H NMR data allowed the differentiation of several positional isomers, in particular those of hydroxylation resulting from the attack of OH radicals on the benzene ring of IOME. Kinetic evolution profiles of main intermediates, end products (NO₃⁻, NH₄⁺, SO₄²⁻) and total organic carbon (TOC) were also examined in detail. From obtained kinetic and analytical results, the presence of privileged sites for the attack of OH radicals was shown and a detailed degradation pathway was proposed.     

Pyrylium salt-photosensitised degradation of phenolic contaminants present in olive oil wastewaters with solar light: Part II. Benzoic acid derivatives

Solar light photodegradation, catalysed by a pyrylium salt, of seven benzoic acids present in olive oil mill, has been studied. Significant percentages of photodegradation (20–40%) have been achieved after 6 h of solar exposure for six of the acids, even though they were expected to be difficult to oxidise, due to the presence of an electron-withdrawing carboxylic acid group directly attached to the aromatic ring. Quenching constants for the electron-transfer process between the substrate and the excited catalyst were calculated by means of fluorescence measurements for syringic acid (66×10⁹ M⁻¹ s⁻¹), gallic acid (51×10⁹ M⁻¹ s⁻¹), veratric acid (51×10⁹ M⁻¹ s⁻¹), vanillic acid (48×10⁹ M⁻¹ s⁻¹), protocatechuic acid (37×10⁹ M⁻¹ s⁻¹) and p-hydroxybenzoic acid (15×10⁹ M⁻¹ s⁻¹); no quenching was found for benzoic acid. These photophysical measurements are in good correlation with the yields obtained in the pyrylium salt photocatalysed degradation of those phenolic acids.     

Photocatalytic degradation kinetics of di- and tri-substituted phenolic compounds in aqueous solution by TiO2/UV

In this study, photocatalytic degradation of 2,4,6-trimethylphenol (TMP), 2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP), 2,4-dimethylphenol (DMP), 2,4-dichlorophenol (DCP) and 2,4-dibromophenol (DBP) has been studied by TiO₂/UV. Although degraded phenolic compound concentration increased by increasing initial concentration photocatalytic decomposition rates of di- and tri-substituted phenols at 0.1–0.5 mM initial concentrations decreased when the initial concentration increased. The fastest degradation observed for TCP and the slowest for TMP. Photodegradation kinetics of the compounds has been explained in terms of Langmuir–Hinshelwood kinetics model. Degradation rate constants have been observed to be extremely depended on electronegativity of the substituents on phenolic ring. Degradation rate constant and adsorption equilibrium constant of TCP were calculated as k 0.0083 mM min⁻¹ and K 9.03 mM⁻¹. For TBP and TMP the values of k and K were obtained as 0.0040 mM min⁻¹, 19.20 mM⁻¹, and 0.0017 mM min⁻¹, 51.68 mM⁻¹, respectively. Degradation rate constant of DBP was similar as DCP (0.0029 mM min⁻¹ for DBP and 0.0031 mM min⁻¹ for DCP) whereas adsorption equilibrium constants differed (48.40 mM⁻¹ for DBP and 30.52 mM⁻¹ for DCP). K and k of DMP found as 83.68 mM⁻¹ and 0.0019 mM min⁻¹, respectively. The adsorption equilibrium constants in the dark were ranged between 1.11 and 3.28 mM⁻¹ which are lower than those obtained in kinetics. Adsorption constants have inversely proportion with degradation rate constants for all phenolic compounds studied.     

Activity, selectivity and durability of VO–ZSM-5 catalysts for the selective catalytic reduction of NO by ammonia

ZSM-5 zeolite was loaded with vanadyl ions (VO²⁺) by treatment of Na–ZSM-5 with aqueous VOSO₄ solution at pH 1.5–2. The catalytic material was tested for the selective catalytic reduction of NO with ammonia at temperatures between 473 and 823 K and normal pressure using a feed of 1000 ppm NO, 1000 (or 1100) ppm NH₃ and 2% O₂ in He. The catalyst proved to be highly active, providing, e.g. initial NO conversions of >90% at 620 l g⁻¹ h⁻¹ (≈400 000 h⁻¹) and 723 K, and selective, providing nitrogen yields equal to NO conversion at equimolar feed in a wide temperature range and only minor N₂O formation at NH₃ excess. Admixture of SO₂ (200 ppm) resulted in an upward shift of the useful temperature range, but did not affect the catalytic behaviour at temperatures ≥623 K. No SO₂ conversion was noted at T ≤ 723 K and 450 l g⁻¹ h⁻¹. The poisoning effect of water (up to 4.5 vol%) was weak at temperatures between 623 and 773 K. VO-ZSM-5 catalysts are gradually deactivated already under dry conditions, probably by oxidation of the vanadyl ions into pentavalent V species. This deactivation is considerably accelerated in the presence of water.     

On-stream modification of MFI zeolite membranes for enhancing hydrogen separation at high temperature

-Alumina-supported MFI zeolite membranes were modified by on-stream catalytic thermal cracking of methyldiethoxysilane (MDES) molecules inside the zeolitic channels during the separation of H₂/CO₂ gas mixture at 450 °C and atmospheric pressure. The MDES vapor was carried by the H₂/CO₂ feed gas and the effect of modification was monitored continuously through online analysis of the permeate stream. The modified membrane exhibited a significant increase in H₂ selectivity over CO₂ with a moderate decrease in H₂ permeance. At 450 °C, the modified MFI membrane obtained a H₂/CO₂ permselectivity of 17.5 with H₂ single gas permeance of 1.86 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ as compared to a permselectivity of 2.78 and permeance of 2.75 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ for the membrane before modification. The modified membrane also showed good performance and stability in separation of H₂/CO₂ gas mixture containing up to 28.4% water vapor at 450 °C and atmospheric pressure.     

Catalytic behavior of the Fe/Fe system in the electro-Fenton degradation of the antimicrobial chlorophene

The catalytic behavior of the Fe³⁺/Fe²⁺ system in the electro-Fenton degradation of the antimicrobial drug chlorophene has been studied considering four undivided electrolytic cells, where a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂-diffusion cathode have been used. Chlorophene electrolyses have been carried out at pH 3.0 under current control, with 0.05 M Na₂SO₄ as supporting electrolyte and Fe³⁺ as catalyst. In these processes the drug is oxidized with hydroxyl radical (OH) formed both at the anode from water oxidation and in the medium from electrochemically generated Fenton's reagent (Fe²⁺ + H₂O₂, both of them generated at the cathode). The catalytic behavior of the Fe³⁺/Fe²⁺ system mainly depends on the cathode tested. In the cells with an O₂-diffusion cathode, H₂O₂ is largely accumulated and the Fe³⁺ content remains practically unchanged. Under these conditions, the chlorophene decay is enhanced by increasing the initial Fe³⁺ concentration, because this leads to a higher quantity of Fe²⁺ regenerated at the cathode and, subsequently, to a greater OH production from Fenton's reaction. In contrast, when the carbon felt cathode is used, H₂O₂ is electrogenerated in small extent, whereas Fe²⁺ is largely accumulated because the regeneration of this ion from Fe³⁺ reduction at the cathode is much faster than its oxidation to Fe³⁺ at the anode. In this case, an Fe³⁺ concentration as low as 0.2 mM is required to obtain the maximum OH generation rate, yielding the quickest chlorophene removal. Chlorophene is poorly mineralized in the Pt/O₂ diffusion cell because the final Fe³⁺–oxalate complexes are difficult to oxidize with OH. These complexes are completely destroyed using a BDD anode at high current thanks to the great amount of OH generated on its surface. Total mineralization is also achieved in the Pt/carbon felt and BDD/carbon felt cells with 0.2 mM Fe³⁺, because oxalic acid and its Fe²⁺ complexes are directly oxidized with OH in the medium. Comparing the four cells, the highest oxidizing power regarding total mineralization is attained for the BDD/carbon felt cell at high current due to the simultaneous destruction of oxalic acid at the BDD surface and in the bulk solution.