photoelectro-Fenton Research Articles

Sulfamethoxazole mineralization by solar photo electro-Fenton process in a pilot plant

The sulfamethoxazole (SMX) mineralization through the solar photo electro-Fenton (SPEF) process in a pilot plant containing 20L of 50mgL−1 SMX solution was investigated. The process was carried out at pH 3 under different operational conditions varying temperature, volumetric flow and applied current density. Box-Behnken experimental design and response surface methodology (RSM) were used to optimize the experimental variables of the SPEF process. Under the optimal conditions, the SPEF was compared with electro-Fenton (EF) and anodic oxidation (AO- H2O2) processes. Under optimum design variables of 47mAcm−2, 45°C and 571Lh−1, SPEF was more efficient yielding 90% of TOC removal after 360min of reaction with a maximum of 83% of mineralization current efficiency (MCE). The main by-products detected on the final solution treated by SPEF were oxalic, maleic, oxamic and fumaric acids, while NH4+ and NO3− were the main inorganic nitrogen ions released during the process.

Degradation of herbicide S-metolachlor by electrochemical AOPs using a boron-doped diamond anode

The degradation and mineralization ability of electrochemical processes like electro-oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and UVA-assisted photoelectro-Fenton (PEF) has been comparatively studied for solutions of the herbicide S-metolachlor. Solutions of 100mL have been treated using an undivided cell equipped with an air-diffusion cathode and a boron-doped diamond (BDD) anode. The effect of pH, current density, and Fe2+ and S-metolachlor concentrations has been thoroughly studied. The total organic carbon removal profiles have demonstrated the feasibility of almost overall mineralization by EF and PEF after 9h at 300mA. The herbicide decays in both treatments informed about the complexation of Fe(III) ions formed from Fenton’s reaction, which decelerated S-metolachlor removal. However, the high oxidation power of BDD anode allowed the gradual mineralization of such complexes. The identification of chlorinated and non-chlorinated degradation byproducts by GC–MS has allowed the proposal of main degradation routes.

Electrochemical advanced oxidation of carbofuran in aqueous sulfate and/or chloride media using a flow cell with a RuO2-based anode and an air-diffusion cathode at pre-pilot scale

The treatment of 0.348 mM carbofuran solutions in 0.050 M Na2SO4 at pH 3.0 has been studied by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). The trials were performed in a 2.5 L pre-pilot plant equipped with a filter-press cell, which contained a RuO2-based anode and an air-diffusion cathode, connected to an annular photoreactor with a 160 W UVA lamp in PEF. The oxidizing species were the OH generated at the anode from water oxidation and in the bulk from Fenton’s reaction between added Fe2+ and H2O2 produced at the cathode. The oxidation power of treatments rose in the order EO-H2O2 ≪ EF < PEF, demonstrating the preponderant role of OH in the bulk. The drug decay always obeyed a pseudo-first order kinetics. Similar TOC abatements of 82%–88% were found in PEF operating at different current densities and carbofuran concentrations, ascribed to the additional photolytic action of UVA light to remove photoactive intermediates, also allowing a gradual detoxification. In matrices with Cl−, active chlorine was also produced as oxidant and its quick reaction with carbofuran caused its faster decay at increasing Cl− content. However, lower mineralization was achieved because of the accumulation of recalcitrant chloroderivatives. GC–MS analysis of treated solutions with 0.070 M NaCl corroborated the formation of 6 chloroderivatives, whereas 5 heteroaromatics were detected in 0.050 M Na2SO4. Oxalic acid was accumulated in the latter medium since its Fe(III) complexes were stable in EF and rapidly mineralized by UVA light in PEF. The mineralization of urban wastewater spiked with carbofuran by PEF in the pre-pilot plant was partial due to the recalcitrant chloroderivatives formed from carbofuran and natural organic matter.

Electrochemical Fenton-based treatment of tetracaine in synthetic and urban wastewater using active and non-active anodes

The electrochemical degradation of tetracaine hydrochloride has been studied in urban wastewater. Treatments in simulated matrix with similar ionic composition as well as in 0.050 M Na2SO4 were comparatively performed. The cell contained an air-diffusion cathode for H2O2 electrogeneration and an anode selected among active Pt, IrO2-based and RuO2-based materials and non-active boron-doped diamond (BDD). Electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) were comparatively assessed at pH 3.0 and constant current density. The pharmaceutical and its byproducts were oxidized by OH formed from water oxidation at the anode surface and in the bulk from Fenton's reaction, which occurred upon addition of 0.50 mM Fe2+ in all media, along with active chlorine originated from the anodic oxidation of Cl− contained in the simulated matrix and urban wastewater. The PEF process was the most powerful treatment regardless of the electrolyte composition, owing to the additional photolysis of intermediates by UVA radiation. The use of BDD led to greater mineralization compared to other anodes, being feasible the total removal of all organics from urban wastewater by PEF at long electrolysis time. Chlorinated products were largely recalcitrant when Pt, IrO2-based or RuO2-based anodes were used, whereas they were effectively destroyed by BDD(OH). Tetracaine decay always obeyed a pseudo-first-order kinetics, being slightly faster with the RuO2-based anode in Cl− media because of the higher amounts of active chlorine produced. Total nitrogen and concentrations of NH4+, NO3−, ClO3−, ClO4− and active chlorine were determined to clarify the behavior of the different electrodes in PEF. Eight intermediates were identified by GC-MS and fumaric and oxalic acids were quantified as final carboxylic acids by ion-exclusion HPLC, allowing the proposal of a plausible reaction sequence for tetracaine mineralization by PEF in Cl−-containing medium.

Electro-Fenton, UVA Photoelectro-Fenton and Solar Photoelectro-Fenton Treatments of Organics in Waters Using a Boron-Doped Diamond Anode: A Review

The characteristics and applications of electrochemical advanced oxidation processes (EAOPs) like electro-Fenton (EF), UVA photoelectro-Fenton (PEF) and solar PEF (SPEF) with a boron-doped diamond (BDD) anode are reviewed. Their oxidative properties are based on the attack of •OH formed at the anode surface and in the medium from Fenton’s reaction between cathodically generated H2O2 and added Fe2+. The illumination with UVA light in PEF and sunlight in SPEF enhances the degradation process due to the photolysis of complexes of Fe(III) with generated carboxylic acids. Examples on the removal of industrial chemicals, pesticides, dyes and pharmaceuticals by these EAOPs using bench-scaled stirred tank reactors and pre-pilot plants are described. The influence of experimental variables on the mineralization and energetic parameters is detailed. The decay kinetics of pollutants and the evolution of intermediates are discussed. The SPEF process shows the best performance, being the most potent EAOP tested.

Electrochemical Hydrogen Peroxide Production in Acidic Medium Using a Tubular Photo-reactor: Application in Advanced Oxidation Processes

This paper describes the results obtained in the design and characterization of a tubular electrochemical reactor. The set-up was employed for on-site hydrogen peroxide (H2O2) production in an acidic medium (pH 3) to promote three electrochemical advanced oxidation processes (EAOP): electro-Fenton (EF), photoelectro-Fenton (PEF) and photocatalysis treatment (PT). These processes were evaluated by their abilities to degrade a commercial dye, Orange-II (OGII), in solution using total organic carbon (TOC) removal and high performance liquid chromatography (HPLC). To have free solutions of iron in the EF and PEF systems, a NafionTM membrane with dispersed iron was prepared. For use in photocatalysis, electrodes with a large superficial area were prepared by coating carbon cloth fiber supports with titanium dioxide (TiO2) using the electrophoretic (EP) method. In this work, wastewater samples with a large number of microorganisms (coliform bacteria) were treated with this new reactor design.

Role of sulfate, chloride, and nitrate anions on the degradation of fluoroquinolone antibiotics by photoelectro-Fenton.

Taking ciprofloxacin (CIP) as a fluoroquinolone antibiotic model, this work explores the role of common anions (sulfate, nitrate, and chloride) during the application of photoelectro-Fenton (PEF) at natural pH to degrade this type of compound in water. The system was composed of an IrO2 anode, Ti, or gas diffusion electrode (GDE) as cathode, Fe2+, and UV (254nm). To determine the implications of these anions, the degradation pathway and efficiency of the PEF sub-processes (UV photolysis, anodic oxidation, and electro-Fenton at natural pH) were studied in the individual presence of the anions. The results highlight that degradation routes and kinetics are strongly dependent on electrolytes. When chloride and nitrate ions were present, indirect electro-chemical oxidation was identified by electro-generated HOCl and nitrogenated oxidative species, respectively. Additionally, direct photolysis and direct oxidation at the anode surface were identified as degradation routes. As a consequence of the different pathways, six primary CIP by-products were identified. Therefore, a scheme was proposed representing the pathways involved in the degradation of CIP when submitted to PEF in water with chloride, nitrate, and sulfate ions, showing the complexity of this process. Promoted by individual and synergistic actions of this process, the PEF system leads to a complete elimination of CIP with total removal of antibiotic activity against Staphylococcus aureus and Escherichia coli, and significant mineralization. Finally, the role of the anions was tested in seawater containing CIP, in which the positive contributions of the anions were partially suppressed by its OH radical scavenger action. The findings are of interest for the understanding of the degradation of antibiotics via the PEF process in different matrices containing sulfate, nitrate, and chloride ions.

Photo-assisted electrochemical degradation of polychlorinated biphenyls with boron-doped diamond electrodes

ABSTRACTThe capacity of the photo electro-Fenton (PEF) process to degrade a mixture of seven polychlorinated biphenyl (PCB) congeners was studied. Boron-doped diamond (BDD) sheets were used as anode and cathode in the experimental electrolytic cell that contained Na2SO4 0.05 M at pH 3 as supporting electrolyte for the electro generation of H2O2 at the cathode. The effects of UV light intensity (254 and 365 nm), current density (8, 16 and 24 mA cm−2) and ferrous ion dosage (0.1, 0.2 and 0.3 mM) on PCB (C0 = 50 μg L−1) degradation were evaluated. The highest level of PCB degradation (97%) was achieved with 16 mA cm−2 of current density, 0.1 mM of ferrous ion and UV light at 365 nm as irradiation source after 6 h of reaction. PCB28, PCB52 and PCB101 were not detected after 0.5, 1.5 and 3 h of reaction, respectively. The degradation of PCB138, PCB153, PCB180 and PCB209 was also high (>95%). The PEF system outperformed other oxidation processes (electro-Fenton, anodic oxidation, Fenton, photo-Fenton and UV photolysis) in terms of reaction rate and degradation efficiency. These results demonstrate for the first time the degradation of PCB209, the most highly chlorinated PCB congener, by an advanced electrochemical oxidation process.

Efficient mineralization of antibiotic ciprofloxacin in acid aqueous medium by a novel photoelectro-Fenton process using a microwave discharge electrodeless lamp irradiation

In this study, a novel photoelectro-Fenton (PEF) process using microwave discharge electrodeless lamp (MDEL) as a UV irradiation source was developed for the removal of antibiotic ciprofloxacin (CIP) in water. Comparative degradation of 200mgL−1 CIP was studied by direct MDEL photolysis, anodic oxidation (AO), AO in presence of electrogenerated H2O2 (AO-H2O2), AO-H2O2 under MDEL irradiation (MDEL-AO-H2O2), electro-Fenton (EF) and MDEL-PEF processes. Higher oxidation power was found in the sequence: MDEL photolysis < AO < AO-H2O2< MDEL-AO-H2O2< EF < MDEL-PEF. Effects of current density, pH, initial Fe2+ concentration and initial CIP concentration on TOC removal in MDEL-PEF process were examined, and the optimal conditions were ascertained. The releases of three inorganic ions (F−, NH4+ and NO3−) and two carboxylic acids (oxalic and formic acids) were qualified. Seven aromatic intermediates mainly generated from hydroxylation, dealkylation and defluorination of CIP were detected by UPLC-QTOF-MS/MS technology. Therefore, plausible degradation sequences for CIP degradation in MDEL-PEF process including all detected products were proposed.

Effect of UV light on pentachlorophenol removal in the electroFenton process

Background: This research studied the effect of UV light on pentachlorophenol (PCP) removal in the electro-Fenton (EF) process. Methods: PCP was used as the pollutant in this study. The effects of Fenton’s reagent, i.e. hydrogen peroxide concentration, solution pH, and treatment time by EF (EF) and photoelectro-Fenton (PEF) processes, were studied to determine rates of PCP removal. The results showed that a better performance and a high removal efficiency were achieved by coupling UV radiation and the EF process. Results: EF processes required more time to remove PCP, while after a reaction time of 10 minutes, the PEF achieved a removal efficiency of 90.4%; this value is higher than the maximum efficiency of the EF process (83.44% after 40 minutes). The kinetic mechanisms of both processes were examined and compared. The rate constants at optimum conditions were 0.0455 and 0.0579 min−1 for EF and PEF processes, respectively. Conclusion: Removal efficiency was obtained in the order of PEF > EF. Keywords: Ultraviolet rays, Reaction Time, Kinetics.

Removal of atrazine and its by-products from water using electrochemical advanced oxidation processes

Atrazine (ATZ) is one of the most common pesticides detected in surface water in Quebec (Canada). The present study was mainly focused on the degradation of ATZ and its by-products using electrochemical advanced oxidation processes such as photo-electro-Fenton (PEF), electro-Fenton (EF) and anodic-oxidation with simultaneous H2O2 formation (AO - H2O2). The comparison of these processes showed that PEF process was found to be the most effective process in removing ATZ and its by-products from both synthetic solution (ATZ0 = 100 μg L−1) and real agricultural surface water enriched with ATZ (ATZ0 = 10 μg L−1). Different operating parameters, including wavelength of the light, pH, current density and the presence of natural organic matter (humic acids) were investigated for PEF process using boron-doped diamond (BDD) anode and graphite cathode. The current density and the wavelength of the light were the most important parameters in the ATZ degradation efficiency. The best operating conditions were recorded for the synthetic samples at a current density of 18.2 mA cm−2, a pH of 3.0 and treatment time of 45 min. Results showed that atrazine-desethyl-desisopropyl (DEDIA) was the most important by-product recorded. More than 99% of ATZ oxidation was recorded after 15 min of treatment and all the concentrations of major by-products were less than the limit of detection after 45 min of treatment. The PEF process was also tested for real surface water contaminated by ATZ: i) with and without addition of iron; ii) without pH adjustment (pH ∼ 6.7) and with pH adjustment (pH ∼ 3.1). In spite of the presence of radical scavenger and iron complexation the PEF process was more effective to remove ATZ from real surface water when the pH value was adjusted near to 3.0. The ATZ removal was 96.0% with 0.01 mM of iron (kapp = 0.13 min−1) and 100% with 0.1 mM of iron (kapp = 0.17 min−1).

Electrochemical Treatment of 4-Hydroxyphenylacetic Acid in Olive Oil Mill Wastewater

INTRODUCTION The decontamination of olive oil mill wastewater (OMWW) is of great interest in Mediterranean countries as the main producers of olive oil worldwide. The large variety of recalcitrant substances contained in OMWW and the difficulty to remove them or recycle the large volumes of wastewater encourage the development of new technologies for decontamination, like electrochemical advanced oxidation processes (EAOPs) that present high performance for recalcitrant compounds [1,2]. 4-Hydroxyphenylacetic acid (4-HPA) is a main component of this kind of wastewater [3]. This communication presents the effective removal of 4-HPA from an OMWW matrix by EAOPs including anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF). EXPERIMENTAL Analytical grade 4-HPA was purchased from Sigma. The OMWW was provided by a local company of olive oil extraction, which was characterized by analyzing its metal content, BOD, COD, TOC, conductance, TS, TDS and organic components before use. As a first step, the OMWW was filtered with a 45 µm cloth. As a second step, several mixtures with 100 mg L-1 TOC of 4-HPA in OMWW were prepared. The OMWW/water ratio was varied from 20/80 to 100/0 v/v. Experiments were also carried out using 100 mg L-1 TOC of 4-HPA in 50 mM of Na2SO4 to clarify the matrix effect. AO-H2O2, EF and PEF experiments were performed with 100 mL of each solution at pH 3.0 and 25 ºC using a stirred tank reactor with a 3 cm2 boron-doped diamond (BDD) anode and a 3 cm2 carbon-polytetrafluoroethylene air-diffusion cathode by applying 16.7 mA cm-2 for 540 min. In the two latter methods, 0.50 mM Fe2+ was added as catalyst for Fenton’s reaction. PEF trials were run with a 6W UVA light. RESULTS The characteristics of the real OMWW were: 505.35 mg L-1 of TOC, 1.51 mS of conductance, 1600 mg L-1 of BOD, 5536 mg L-1 of TS and 82 mgL-1 of TDS. For each method, a gradual decay in TOC was found as the OMWW ratio in the sample increased. For example, a final TOC removal of 89% was achieved by AO-H2O2 in 50 mM Na2SO4, whereas it was reduced by 75% in a 60/40 OMWW/water mixture and 60% in pure OMWW. The best results were obtained by PEF, with final TOC decays of 98%, 88% and 87% in a the above media due to the combined action of ●OH produced at the BDD surface from water oxidation, the ●OH formed during Fenton’s reaction and the extra decomposition of Fe(III)-carboxylate complexes by UVA light. The kinetic assays also showed a drop in 4-HPA decay with raising OMWW content. Thus, total disappearance of the substrate was attained in 360 min by AO-H2O2 in 50 mM Na2SO4 and in 500 min for the other solutions. For the best process (i.e., PEF), these times diminished to 60 and 80 min, respectively. CONCLUSIONS 4-HPA can be effectively degraded in an OMWW matrix using the EAOPs studied, especially PEF. This process was the most efficient one, reaching an almost total mineralization, to a larger extent in pure Na2SO4. The decay and mineralization of 4-HPA rose in the order AO-H2O2 < EF < PEF, regardless of the matrix used. The oxidation power of ●OH formed from water oxidation at the BDD surface in AO-H2O2 was strongly enhanced by the additional ●OH in the bulk from Fenton’s reaction, being the degradation improved under the potent action of UVA irradiation in PEF. For all the EAOPs studied, the presence of OMWW decelerated TOC removal and 4-HPA decay. This can be related to the parallel reactions of ●OH with the organic components present in OMWW that act as oxidant scavengers. ACKNOWLEDGEMENTS We are grateful for economical support from project CTQ2016-78616-R (MINECO, FEDER, EU) and for the scholarship given to N.E Flores from SENESCYT (Ecuador). BIBLIOGRAPHY [1] A. Thiam, E. Brillas, F. Centellas, P.L. Cabot, I. Sirés, Electrochemical reactivity of Ponceau 4R (food additive E124) in different electrolytes and batch cells, Electrochim. Acta 173 (2015) 523. [2] A. Thiam, E. Brillas, J.A. Garrido, R.M. Rodríguez, I. Sirés, Routes for the electrochemical degradation of the artificial food azo-colour Ponceau 4R by advanced oxidation processes, Appl. Catal. B: Environ. 180 (2016) 227. [3] C. Belaid, M. Khadraoui, S. Mseddi, M. Kallel, B. Elleuch, J.F. Fauvarque, Electrochemical treatment of olive mill wastewater: Treatment extent and effluent phenolic compounds monitoring using some uncommon analytical tools, J. Environ. Sci. 25 (2013) 220.

On the selection of the anode material for the electrochemical removal of methylparaben from different aqueous media

Parabens are widely used industrial preservatives, routinely found in wastewater along with major inorganic ions like sulfate and chloride. This work investigates the oxidation ability of three electrochemical processes in tank reactors equipped with an air-diffusion cathode to electrogenerate H2O2 on site, namely electro-oxidation (EO-H2O2), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF), to degrade aqueous solutions of methylparaben (MeP) at pH 3.0. Their performance using boron-doped diamond (BDD), Pt or two kinds of dimensionally stable anodes (DSA®) has been compared from the analysis of mineralization profiles and decay kinetics in the presence of sulfate and/or chloride ions. The use of BDD ensured the overall mineralization in all three processes according to the sequence: PEF>EF>EO-H2O2, thanks to the contribution of BDD(OH), OH and UVA light. Pt and DSA® became an interesting alternative in PEF, with slower organic matter removal but similar final mineralization percentages, being much less powerful than BDD in EO-H2O2. The presence of Cl− was beneficial in the latter process, due to the formation of active chlorine as an additional oxidant that caused a much faster decay of MeP. Conversely, it became significantly detrimental in EF due to the partial destruction of H2O2 and OH in the bulk by active chlorine and Cl−, respectively. The oxidation power of PEF was so high that similar fast, complex decay kinetics was found in all media regardless of the anode, although the mineralization was decelerated owing to the accumulation of chlorinated by-products. GC-MS and HPLC analysis allowed the identification of up to seven aromatic MeP derivatives in sulfate+chloride mixtures, including three non-chlorinated compounds also found in pure sulfate medium. These molecules were gradually transformed into oxalic acid, along with four chlorinated aliphatic carboxylic acids in Cl−-containing media.

Abatement of the fluorinated antidepressant fluoxetine (Prozac) and its reaction by-products by electrochemical advanced methods

The degradation of the fluorinated antidepressant fluoxetine, as hydrochloride, was comparatively studied in sulfate medium at pH 3.0 by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). Experiments were performed with 100mL solutions in an undivided tank reactor equipped with a Pt, RuO2-based or boron-doped diamond (BDD) anode and an air-diffusion cathode for continuous H2O2 production. The BDD anode showed higher mineralization rate due to the great production of physisorbed BDD(OH), which has large reactivity to oxidize the drug and intermediates. The degradation rate was enhanced by EF with 0.50mM Fe2+ due to the additional production of OH in the bulk from Fenton’s reaction. The degradation was even faster using PEF owing to the additional photolytic action of UVA radiation. The most effective process was PEF with a BDD anode achieving 94% mineralization at 300min. The fluoxetine decay followed a pseudo-first-order kinetics, being quicker in the order:AO-H2O2<EF<PEF. The effect of the current density and drug concentration on the mineralization rate and fluoxetine decay was clarified. Oxidation of fluoxetine by hydroxyl radicals yielded four aromatic by-products, as found by GC–MS. Additionally, a chloroaromatic compound was identified as a result of the reaction of active chlorine, which was formed in situ from the oxidation of chloride ion at the BDD anode. Four short-chain linear carboxylic acids, being oxalic and formic acid more abundant, were identified. In PEF, fluorine atoms of fluoxetine were completely released as fluoride ion, whereas the initial nitrogen was converted into nitrate ion in all cases. A reaction pathway for fluoxetine mineralization by the electrochemical advanced methods is finally proposed.

4-Hydroxyphenylacetic acid oxidation in sulfate and real olive oil mill wastewater by electrochemical advanced processes with a boron-doped diamond anode

The degradation of 4-hydroxyphenylacetic acid, a ubiquitous component of olive oil mill wastewater (OOMW), has been studied by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF). Experiments were performed in either a 0.050M Na2SO4 solution or a real OOMW at pH 3.0, using a cell with a boron-doped diamond (BDD) anode and an air-diffusion cathode for H2O2 generation. Hydroxyl radicals formed at the BDD surface from water oxidation in all processes and/or in the bulk from Fenton’s reaction between added Fe2+ and generated H2O2 in EF and PEF were the main oxidants. In both matrices, the oxidation ability of the processes increased in the order AO-H2O2<EF<PEF. The superiority of PEF was due to the photolytic action of UVA radiation on photosensitive by-products, as deduced from the quick removal of Fe(III)-oxalate complexes. The effect of current density and organic content on the performance of all treatments was examined. 4-Hydroxyphenylacetic acid decay obeyed a pseudo-first-order kinetics. The PEF treatment of 1.03mM 4-hydroxyphenylacetic acid in 0.050M Na2SO4 allowed 98% mineralization at 360min even at low current density, whereas 80% mineralization and a significant enhancement of biodegradability were achieved with the real OOMW.

Tertiary treatment of a municipal wastewater toward pharmaceuticals removal by chemical and electrochemical advanced oxidation processes

This study focuses on the degradation of pharmaceuticals from a municipal wastewater after secondary treatment by applying various advanced oxidation processes (AOPs) and electrochemical AOPs (EAOPs) like UVC, H2O2/UVC, anodic oxidation (AO), AO with electrogenerated H2O2 (AO-H2O2), AO-H2O2/UVC and photoelectro-Fenton (PEF) using either UVC radiation (PEF-UVC) or UVA radiation (PEF-UVA). The municipal wastewater after secondary treatment was spiked with 5.0 mg L−1 of trimethoprim (TMP) antibiotic. The efficiency of processes to remove TMP followed the order UVC < AO-H2O2 < PEF-UVA << AO ≈ PEF-UVC < AO-H2O2/UVC < PEF-UVA (pH = 2.8) < H2O2/UVC ≈ PEF-UVC (pH = 2.8), using neutral pH, except when identified. While the UVC radiation alone led to a very low TMP removal, the H2O2/UVC process promoted a very high TMP degradation due to the production of hydroxyl radicals (OH) by H2O2 cleavage. In the AO-H2O2/UVC process, the electrogeneration of H2O2 can avoid the risks associated with the transportation, storage and manipulation of this oxidant and, furthermore, OH at the anode surface are also formed. Nevertheless, low contents of H2O2 were detected mainly at the beginning of the reaction, leading to a lower initial reaction rate when compared with the H2O2/UVC system. In the PEF-UVC, the addition of iron at neutral pH led to the visible formation of insoluble iron oxides that can filter the light. At pH 2.8, the iron remained dissolved, thereby promoting the Fenton's reaction and increasing the organics removal. The UVA-driven processes showed limited efficiency when compared with those using UVC light. For all processes with H2O2 electrogeneration, the active chlorine species can be scavenged by the H2O2, diminishing the efficiency of the processes. This can explain the lower efficiency of AO-H2O2 when compared with AO. Moreover, the degradation of the MWWTP effluent spiked with 18 pharmaceuticals in μg L−1 during AO process was assessed as well as the influence of the following operational variables on the process efficiency: (i) H2O2 concentration on H2O2/UVC, (ii) current density on AO, AO-H2O2, AO-H2O2/UVC, PEF-UVC and PEF-UVA, and (iii) pH on PEF-UVA.

Assessment of LED-assisted electro-Fenton reactor for the treatment of winery wastewater

Winery wastewaters prove to be an environmental issue due to their particular characteristics (high COD and TOC, colour and low pH) as well as their seasonal generation. In this work, a new sequential reactor design, based on photo electro-Fenton technology combined with LED radiation, has been demonstrated as a viable alternative for the treatment of these wastewaters. The optimization of the working parameters led to achieve high colour and TOC removals in simulated effluents with significant initial TOC values. The energy consumption was a key factor in these hybrid processes and it was found that the process carried out in the new designed reactor was a cost effective treatment with around 1KWh/gTOCremoved. Finally the validation of the designed reactor was successfully performed for the treatment of real winery wastewater.

Influence of the anode material on the degradation of naproxen by Fenton-based electrochemical processes

This study focuses on the role of the anode material for the electrochemical degradation of the top-selling anti-inflammatory drug naproxen (NPX). Aqueous solutions containing 40mgL−1 NPX sodium in 0.050M NaClO4 at pH 3.0 were comparatively treated by electrochemical advanced oxidation processes (EAOPs) like electro-oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF). The experiments were performed in a 2.5L flow plant equipped with an annular glass photoreactor coupled to a cell with a Pt, IrO2-based (DSA-O2), RuO2-based (DSA-Cl2) or boron-doped diamond (BDD) anode and an air-diffusion cathode to electrogenerate H2O2. In EF and PEF, 0.50mM Fe2+ was added as catalyst. At 50mAcm−2, the oxidation power of EAOPs rose in the order: EO-H2O2<EF<PEF, regardless of the anode used. The IrO2-based anode led to greater mineralization in EO-H2O2 and EF. In contrast, the BDD anode allowed an almost total mineralization in PEF, being superior to 85% attained with the other three materials. DSA, a significantly cheap anode compared to Pt and BDD, can then be a suitable candidate for treating NPX solutions by EAOPs. For each process, the mineralization current efficiency and specific energy consumption were determined. The NPX concentration decay always followed a pseudo-first-order kinetics and, in PEF, it was enhanced in the sequence: RuO2-based<Pt<BDD<IrO2-based. GC–MS analysis of treated solutions allowed detecting six aromatic products, whereas maleic and oxalic acids were identified by ion-exclusion HPLC. A reaction sequence for the degradation of NPX by EAOPs is finally proposed.

Elimination of radiocontrast agent diatrizoic acid by photo-Fenton process and enhanced treatment by coupling with electro-Fenton process.

The removal of radiocontrast agent diatrizoic acid (DIA) from water was performed using photo-Fenton (PF) process. First, the effect of H2O2 dosage on mineralization efficiency was determined using ultraviolet (UV) irradiation. The system reached a maximum mineralization degree of 60% total organic carbon (TOC) removal at 4h with 20mM initial H2O2 concentration while further concentration values led to a decrease in TOC abatement efficiency. Then, the effect of different concentrations of Fenton's reagents was studied for homogeneous Fenton process. Obtained results revealed that 0.25mM Fe(3+) and 20mM H2O2 were the best conditions, achieving 80% TOC removal efficiency at 4h treatment. Furthermore, heterogeneous PF treatment was developed using iron-activated carbon as catalyst. It was demonstrated that this catalyst is a promising option, reaching 67% of TOC removal within 4h treatment without formation of iron leachate in the medium. In addition, two strategies of enhancement for process efficiency are proposed: coupling of PF with electro-Fenton (EF) process in two ways: photoelectro-Fenton (PEF) or PF followed by EF (PF-EF) treatments, achieving in both cases the complete mineralization of DIA solution within only 2h. Finally, the Microtox tests revealed the formation of more toxic compounds than the initial DIA during PF process, while, it was possible to reach total mineralization by both proposed alternatives (PEF or PF-EF) and thus to remove the toxicity of DIA solution.

Incineration of acidic aqueous solutions of dopamine by electrochemical advanced oxidation processes with Pt and BDD anodes

The degradation of 1.04mM of the drug dopamine hydrochloride (100mgL−1 of dissolved organic carbon (DOC)) solutions of pH3.0 has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation (AO) with a Pt anode and AO, electro-Fenton (EF) and photoelectro-Fenton (PEF) with a boron-doped diamond (BDD) anode. The AO processes were performed with a stainless steel cathode, whereas EF and PEF used an air-diffusion cathode that produced H2O2·AO with a Pt anode led to very poor mineralization because of the low oxidizing ability of OH formed at the Pt surface. The use of a BDD anode in AO yielded faster incineration due to the much greater oxidation of OH generated by BDD. The production of OH in the bulk from Fenton's reaction enhanced largely the mineralization process in EF, which was upgraded in PEF by the photodecomposition of some intermediates by UVA light. Almost total mineralization with 97% DOC removal was found after 360min of EF and 240min of the most powerful PEF at 100mAcm−2. The rise in current density from 16.7 to 100mAcm−2 caused increasing DOC reduction for all EAOPs. The change in mineralization current efficiency and specific energy consumption per unit DOC mass was also discussed. Generated short-linear carboxylic acids like maleic, tartronic, glycolic, acetic, oxalic, oxamic and formic were identified by ion-exclusion HPLC. These acids were quickly removed in EF and more rapidly in PEF due to the photolysis of their Fe(III) complexes. Ion chromatography revealed the pre-eminent generation of NH4+ ion along with a lower proportion of NO3− ion. This technique also confirmed the oxidation of the starting Cl− ion at both Pt and BDD anodes with high ClO4− production using BDD.