Solar photoelectro-Fenton Process Research Articles

A novel MOF-derived Fe/Ce@NPC-600 floating cathode with massive FeII using in photoelectro-Fenton system for efficient degradation of aqueous tetracycline: Fabrication, performance prediction based on machine learning and mechanism

A MOF-derived carbon/metaloxide composite (Fe/Ce@NPC-600) by doping Ce into NH2-MOF-101(Fe) precursor and simple one-step carbonization was fabricated. Fe/Ce@NPC-600 as a floating cathode was innovatively applied to the solar photoelectro-Fenton (SPEF) process to increase the yield of H2O2 and activate it for degradation tetracycline (TC). The characterizations showed that the presence of Ce greatly increased the content of Fe2+ and photoresponse ability in the material. Thanks to the synergistic effect of Fe and Ce, Fe/Ce@NPC-600 cathode could efficiently degrade TC by 98.2% within 30 min, and the removal rate of total organic carbon (TOC) was 68.2%, and the photoelectric synergistic enhancement factor (fPEF) was 1.4. Besides, based on machine learning, a extreme gradient boosting model was established to predict electrode performance. The degradation mechanism and pathway of TC were also proposed. Our results inspired the application of floating cathodes, MOF-derived materials and artificial intelligence for advanced oxidation processes for efficient removal of emerging contaminants.

A Review on Electrochemical Advanced Oxidation Treatment of Dairy Wastewater

Dairy wastewater (DW) contains a high concentration of organic and inorganic pollutants. In recent years, extensive research has been conducted to develop more efficient techniques for the treatment of DW. Electrochemical advanced oxidation processes (EAOPs) have gained significant attention among the various treatment approaches. EAOPs rely on electrochemical generation of hydroxyl radicals (•OH) which are considered highly potent oxidizing compounds for the degradation of pollutants in DW. In this paper, we provide an overview of the treatment of DW using various EAOPs, including anodic oxidation (AO), electro-Fenton (EF), photo electro-Fenton (PEF), and solar photo electro-Fenton (SPEF) processes, both individually and in combination with other techniques. Additionally, we discuss the reactor design and operating parameters employed in EAOPs. The variation in degradation efficiency is due to different oxidizing agents produced in specific approaches and their pollutant degradation abilities. In AO process, •OH radicals generated on electrode surfaces are influenced by electrode material and current density, while EF procedures use Fe2+ to create oxidizing agents both on electrodes and in the DW solution, with degradation mechanisms being affected by Fe2+, pH, and current density; additionally, PEF and SPEF approaches enhance oxidizing component production and pollutant degradation using ultraviolet (UV) light. Integration of EAOPs with other biological processes can enhance the pollutant removal efficiency of the treatment system. There is a scope of further research to exhibit the effectiveness of EAOPs for DW treatment in large scale implementation.

Simultaneous degradation of contaminants of emerging concern and disinfection by solar photoelectro-Fenton process at circumneutral pH in a solar electrochemical raceway pond reactor

Simultaneous contaminants of emerging concern (CECs) removal and wild microorganisms’ inactivation was evaluated by applying solar photoelectro-Fenton (SPEF) process in actual secondary effluent collected from a real municipal wastewater treatment plant (MWWTP). 20 L of a mixture of four CECs was used as model pollutants (200 μg/L of acetaminophen, caffeine, sulfamethazine, and sulfamethoxazole each one). The SPEF process was carried out on fully sunny days, at circumneutral pH using the complex Fe3+-EDDS, in a solar electrochemical – raceway pond reactor (SEC-RPR). Initially, the optimal conditions for CECs degradation were determined using a response surface model based on current density, iron complex concentration and Fe3+-EDDS addition time (to allow previous accumulation of H2O2) as model inputs. A current density of 24.6 mA/cm2, a Fe3+-EDDS complex concentration of 0.089 mM and 3.8 min of previous H2O2 accumulation were the resulting optimum conditions that were afterwards applied for the simultaneous degradation of the CECs synthetic mixture and wild microorganisms inactivation in actual secondary effluent. About 85% CECs removal and complete E. coli inactivation were achieved in 30 min, approximately, while E. faecalis and total coliforms could be inactivated under detection limit in 60 min and 75 min, respectively.

Assessment of photo electro-Fenton and solar photo electro-Fenton processes for the efficient degradation of asulam herbicide

The degradation of asulam herbicide by photo electro-Fenton (PEF) and solar photo electro-Fenton (SPEF) processes was studied using an undivided electrochemical BDD/carbon-felt cell to generate H2O2 continuously. A central composite design combined with response surface methodology was applied to determine the optimal operating conditions of current intensity = 0.30 A, [Fe2+] = 0.3 mM, and [Na2SO4] = 0.11 M at pH 3 to achieve the complete degradation of asulam by electro-Fenton. Subsequently, the SPEF process was more efficient treatment compared to PEF, achieving a complete degradation of asulam and 98% of mineralization in 180 min. Moreover, 4-aminobenzenesulfonamide, 4-aminophenol, and 4-benzoquinone were detected as aromatic intermediates, whereas acetic acid, oxalic acid, and NO3− ions were identified as final degradation by-products. Thus, the SPEF process is an efficient alternative for the complete degradation and mineralization of herbicide asulam in an aqueous solution under natural sunlight.

Greywater treatment by anodic oxidation, photoelectro-Fenton and solar photoelectro-Fenton processes: Influence of relevant parameters and toxicity evolution

In this study, the applicability of factorial design to the treatment of greywater (GW) containing dodecyl-benzene sulfonic acid (LAS) by electrochemical advanced oxidation processes (EAOPs) is demonstrated. At bench scale, anodic oxidation with electrogenerated H2O2 (AO-H2O2) and photoelectro Fenton (PEF) processes were studied following a 23 factorial design with central point insertion, using a first-order mathematical polynomial. In the former process, the combination of a boron-doped diamond (BDD) anode with a carbon-PTFE air-diffusion cathode, both of 3 cm2, yielded a 76% degradation of LAS at 40 mg L−1 along with 52% TOC removal under optimized conditions. The PEF process with 5 mg L−1 Fe2+ at current density of 77.5 mA cm−2 allowed attaining a 63% of LAS degradation and 78% of TOC abatement. The best conditions found for PEF according to the factorial design, in terms of Fe2+ concentration and current density, were applied for the treatment of 10 L of raw GW by solar PEF (SPEF) using a compound parabolic collector (CPC) as solar reactor and a filter-press electrochemical cell. A 70% of LAS removal and a 55% of GW mineralization were attained after 240 min of treatment. Artemia salina toxicity tests were performed with effluents resulting from the different methods under optimum conditions, and the SPEF process was proven to be the most effective and promising EAOP for the reduction of GW toxicity.

Removal of contaminants of emerging concern by solar photo electro-Fenton process in a solar electrochemical raceway pond reactor

This work proposes the degradation of different contaminants of emerging concern (CECs) present in a secondary effluent from a municipal wastewater treatment plant in a solar electrochemical raceway pond reactor (SEC-RPR), applying the solar photo electro-Fenton (SPFE) process. Tap water and a secondary effluent were enriched with 100 µg L−1 of 7 CECs to study the degradation of these compounds by the SPEF process in a SEC-RPR. Among the results obtained, an elimination over 96% and 90% of 5 CECs (progesterone, estradiol, ibuprofen, diclofenac and estrone) was achieved, while sulfamethazine and carbamazepine were eliminated by 73, 37% and 80, 66% after 1 h of treatment, respectively. In turn, a secondary effluent that already achieved the minimum organic load standards established by Chilean regulations was treated in a SEC-RPR by applying different electrochemical advanced oxidation processes (EAOPs). However, regardless of the applied treatment (SPEF, electro-Fenton and electro-oxidation/H2O2), it was possible to further reduce the organic content and even mineralize it. These experiments were performed at pH 3, with Na2SO4 0.05 mM, Fe2+ 0.05 mM and applying a current density of 20 mA cm−2. The SPEF process implemented in a SEC-RPR is presented as an excellent alternative for the treatment of municipal wastewater, due to the large contact area between the effluent and UV radiation, in addition to the continuous and homogeneous generation of H2O2, which allows for the production of hydroxyl radicals in solution, favoring the degradation and mineralization of pollutants.

Enhanced solar photo-electro-Fenton by Theobroma grandiflorum addition during pharmaceuticals elimination in municipal wastewater: Action routes, process improvement, and biodegradability of the treated water

This work shows, for the first time, the use of the autochthonous Amazonian fruit copoazu (COPE, Theobroma grandiflorum) as an enhancer of the solar photoelectroFenton (SPEF) performance. SPEF, using a BDD anode with Na2SO4 or IrO2 anode in NaCl and actual sunlight, was applied to degrade four representative pharmaceuticals (acetaminophen, diclofenac, ciprofloxacin, and sulfamethoxazole) simultaneously in raw municipal wastewater (MWW). The effect of COPE addition on both pharmaceuticals degradation and keeping iron in solution at near-neutral pH is presented. In the SPEF process based on IrO2-NaCl, electrogenerated reactive chlorine species played the main degrading role. Meanwhile, in the BDD-based process, hydroxyl radical and photolysis were the main agents responsible for the elimination of pharmaceuticals. The two SPEF processes, IrO2-NaCl and BDD-Na2SO4, led to ~99 and ~49% of pondered degradation of pharmaceuticals, respectively. The addition of an extract of copoazu to the reactor equipped with the BDD anode improved the elimination, achieving ~70% of pondered removal of the pharmaceuticals. COPE acted as a natural complexing agent, favoring the catalytic cycle of iron in the system. Finally, the biodegradability (using aerobic microorganisms) of the MWW treated by the improved SPEF (with the BDD anode) was tested. It was found that the microorganisms were able to remove up to 54.6% of the organic carbon content in the sample, indicating the high biocompatibility of water resultant from the treatment by the SPEF improved with the copoazu presence.

Upgrading and expanding the electro-Fenton and related processes

The Fenton-based electrochemical advanced oxidation processes are currently recognized as the most effective technologies to achieve fast and complete degradation of target organic contaminants in water. Electro-Fenton was the pioneering process, but a larger mineralization is attained via UV and solar photoelectro-Fenton processes due to the occurrence of key photoreduction reactions. In practice, the decontamination effectiveness turns out to be limited as solution pH increases and the two-electron oxygen reduction reaction occurring at the cathode becomes inefficient or insufficient. Here, we focus on the current opinion in two crucial features of the reviewed processes: (i) trends in cathodic H 2 O 2 electrogeneration, showing the oxygen reduction reaction upgrading upon use of new and/or more sustainable electrocatalysts, cathode configurations and reactor designs; and (ii) advances in iron-based catalysts, with the main purpose of expanding the application to a much wider pH range, eventually surpassing the classical acidic limitation associated to conventional Fenton's reaction.

Electro-Fenton, solar photoelectro-Fenton and UVA photoelectro-Fenton: Degradation of Erythrosine B dye solution

The treatment of Erythrosine B, selected as a model compound, has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) such as electro-Fenton, UVA photoelectro-Fenton and solar photoelectro-Fenton at constant current density. Experiments are performed in a one-compartment cell with a BDD anode, and a commercial carbon felt cathode at pH = 3, treating a volume of 0.3 L in each test. The irradiation plays a crucial role in the increasing of hydroxyl radical production and in the recover of iron catalyst. A faster colour and COD removal degradation are achieved under the light application. UVA photoelectro-Fenton and solar photoelectro-Fenton processes allow degrading COD entirely in 90 min, while a conventional electro-Fenton does not reach 90% COD removal after 2 h. Energy consumptions are a substantial factor in process selection. Photo electro-Fenton with a UVA-100 W lamp has one of the best removal performance, but it becomes not suitable for application due to high energy demand, up to 515.6 kWh m−3, and the UVA system requires the main fraction of this energy. Possible alternatives are proposed to contain costs: the first is the reduction of UVA lamp power to 25 W, maintaining a high-performance removal with an Ec decreasing to 187.9 kWh m−3. Nevertheless, the lowest and competitive energy demands is obtained working with a solar photoelectro-Fenton system, where energy consumption are only related to the electrochemical process (20.9 kWh m−3), and removal is complete.

BiVO4 prepared by the sol–gel doped on graphite felt cathode for ciprofloxacin degradation and mechanism in solar-photo-electro-Fenton

In this research, bismuth vanadate-doped graphite felt (GF-BiVO4) was successfully prepared by sol–gel method, in which BiVO4 owned superior electro-Fenton (EF) and solar-photo-electro-Fenton (SPEF) performance. Combined with the analysis by X-ray diffractometer (XRD), field emission transmission electron microscopy (FE-TEM), nitrogen adsorption–desorption isotherms and cyclic voltammetry (CV), the changes of electrodes were reflected in structure and physicochemical properties. The doping of monoclinic BiVO4 endued GF with a higher surface area and more electro-active sites and better electrode activity in comparison to Raw-GF. Then, the GFs were used as cathodes to detect •OH concentration with coumarin (COU) as probe molecule and to evaluate photoelectric performance with ciprofloxacin (CIP) in photocatalysis, EF and SPEF processes. The results demonstrated that the concentration of •OH followed an order of SPEF> EF> photocatalysis, which was consistent with the removal rate of CIP (99.8%, 99.4% and 21.2%, respectively) on GF-BiVO4 at 5 min. Further, five degradation pathways of CIP in SPEF system were proposed including the attack on piperazine ring, oxidation on cyclopropyl group, decarboxylation and hydroxyl radical addition, oxidation on benzene group and defluorination. The study provides insights into the enhancement of EF and SPEF performance and the degradation pathway of CIP in SPEF.

Elimination of pharmaceutical pollutants by solar photoelectro-Fenton process in a pilot plant

In this study, the simultaneous degradation of antibiotics (ampicillin, sulfamethazine, and tetracycline; and non-steroidal anti-inflammatories (diclofenac and salicylic acid)) including the total organic carbon abatement by solar photoelectro-Fenton process was assessed. Eight liters of solution containing the mixture of the five pharmaceuticals in 1mmolL-1 Fe2+, 0.05molL-1 Na2SO4 at pH3 and 35°C were electrolyzed applying different current densities (j = 10, 25, and 50mAcm-2) in a solar-electrochemical pilot plant. The pilot plant was equipped with an electrochemical filter press cell with a dimensionally stable anode (DSA type) and an air-diffusion cathode coupled to a solar photoreactor exposed directly to sunlight radiation. All pharmaceuticals were degraded during the first 10min. A TOC removal efficiency of 99.2% after 100min of treatment with an energy consumption of 534.23kWh (kgTOC)-1 and 7.15kWhm-3 was achieved. The pharmaceutical concentration decay followed a pseudo-first-order kinetics. The specific energy per unit of mass of ampicillin, diclofenac, salicylic acid, sulfamethazine, and tetracycline was obtained at 11.73, 19.56, 35.2, 11.73, and 39.32kWh (kgPD)-1 for ampicillin, diclofenac, salicylic acid, sulfamethazine, and tetracycline, respectively. With our results, we demonstrated that SPEF is an emerging technology for the treatment of this type of pollutants in short time.

Nanofiltration retentate treatment from urban wastewater secondary effluent by solar electrochemical oxidation processes

Comparison of electrochemical processes at pilot plant scale for the elimination of organic microcontaminants in actual urban wastewater treatment plant secondary effluents pre-treated by nanofiltration ([Cl−] = 1100–2000 mg L−1) membranes (for reducing total volume to be treated and increase water salinity), has been addressed. Anodic oxidation (AO), solar-assisted AO, electro Fenton (EF) and solar photoelectro-Fenton (SPEF) processes have been evaluated by using, when required, ethylenediamine-N,N’-disuccinic acid (EDDS) as complexing agent to maintain iron in solution at natural pH. Target water was spiked with a mix solution of microcontaminants: pentachlorophenol, terbutryn, chlorfenvinphos and diclofenac at initial concentrations of 500 and 100 μg L−1, each. AO and EF processes obtained similar degradation rates as added EDDS competed with microcontaminants for oxidant species. SPEF and solar assisted AO showed that high chloride concentrations was a crucial factor since chlorine species generated by solar-assisted AO were enough for efficient microcontaminant removal avoiding the addition of EDDS. Degradation monitoring of microcontaminants contained in actual urban wastewater treatment plant effluents was carried out by liquid chromatography coupled to hybrid quadrupole-linear ion trap-mass spectrometry.

Enhanced electrodegradation of the Sunset Yellow dye in acid media by heterogeneous Photoelectro-Fenton process using Fe3O4 nanoparticles as a catalyst

This work describes the study of sunset yellow (SY) dye degradation based on the heterogeneous electro-Fenton (EF) process, where Fe3O4 NPs were used as heterogeneous catalysts. The electrochemical system used was an undivided electrochemical cell with single compartment and a gas diffusion electrode (GDE) was used as a working electrode. The SY dye samples were analyzed by UV–vis spectrophotometry, high performance liquid chromatography (HPLC) and total organic carbon (TOC). Fe3O4 NPs were synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N2-physisorption analysis. For the Photoelectro-Fenton (PEF) process, the concentration decay of SY dye was 80 and 99 % in the presence of 0.1 mol L−1 Na2SO4 and 0.13 mol L−1 NaCl respectively. The results of TOC removal, showed that ∼50 % of mineralization was achieved at 90 min. For the solar Photoelectro-Fenton process (SPEF) there was high catalytic yield, i.e., 98.7 % of color removal, 100 % of concentration decay and 71 % of TOC removal at 90 min. of electrolysis. The Fe3O4 NPs stability was confirmed after eight consecutive degradation cycles, showing that there is no loss of catalytic activity at the end of the last cycle. The results obtained by XRD analysis showed that there was no structural alteration in the crystallography of the NPs after 5 h of degradation in both electrolytes. There was no dissolution of Fe2+ ions at the end of electrolysis when the SY dye was subjected to the degradation by EF, PEF and SPEF processes.

Electrosynthesis of Hydrogen Peroxide in a Novel Flow-through Electrochemical Reactor with in Situ generated Oxygen

Most of electrochemical advanced oxidation processes (EAOP´s) such as the electroFenton (EF), photo electroFenton (PEF), solar photo electroFenton (SPEF) and electro-peroxone (E-peroxone) processes use hydrogen peroxide (H2O2) as its core reactant due to its possibility to react with some catalysts (Fe2+, O3) yielding high oxidant hydroxyl radicals to be used in the degradation of persistent organic pollutants [1]. Carbonaceous materials like carbon felt, carbon cloth and reticulated vitreous carbon (RVC) are the most used because of its capability to accumulate H2O2 [2,3]. The use of these materials is often in gas diffusion electrodes which are based in the injection of air from an external source to an air chamber located behind the electrode allowing the dispersion of the gas inside the electrode promoting the oxygen reduction [3]. This work deals with the in situ electrosynthesis of H2O2 in a flow through reactor using RVC as cathode material and Ti|Ir-Ta oxides expanded mesh as anode to improve the oxygen evolution reaction with subsequent reduction of O2 on the RVC to yield H2O2. The electrochemical cell consists of a flow channel where the electrodes are placed along its length, allowing the electrolyte to flow through them forcing the transport of oxygen bubbles inside the porous carbon material for its reduction to H2O2. [1] Sirés I., Brillas., E. Remediation of water pollution caused by pharmaceutical residues sed on electrochemical separation and degradation technologies: A review. Environmental International, 40 (2018) 212-229. [2] Coria G., Pérez T., Sirés I., Nava J.L., Mass transport studies during dissolved oxygen reduction to hydrogen peroxide in a filter-press electrolyzer using graphite felt, reticulated vitreous carbon and boron-doped diamond as cathodes. Journal of Electroanalytical Chemistry, 757 (2015) 225-229. [3] Pérez T., Coria G., Sirés I., Nava J.L., Uribe A.R., Electrosynthesis of hydrogen peroxide in a filter-press flow cell using graphite felt as air-diffusion cathode. Journal of Electroanalytical Chemistry, 812 (2018) 54-58.

Removal of Orange II (OII) dye by simulated solar photoelectro-Fenton and stability of WO2.72/Vulcan XC72 gas diffusion electrode

The objectives of this study were to determine the viability of removing Orange II (OII) dye by simulated solar photoelectro-Fenton (SSPEF) and to evaluate the stability of a WO2.72/Vulcan XC72 gas diffusion electrode (GDE) and thus determine its best operating parameters. The GDE cathode was combined with a BDD anode for decolorization and mineralization of 350 mL of 0.26 mM OII by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) at 100, 150 and 200 mA cm−2 and SSPEF at 150 mA cm−2. The GDE showed successful operation for electrogeneration, good reproducibility and low leaching of W. Decolorization and OII decay were directly proportional to the current density (j). AO-H2O2 had a reduced performance that was only half of the SSPEF, PEF and EF treatments. The mineralization efficiency was in the following order: AO-H2O2 < EF < PEF ≈ SSPEF. This showed that the GDE, BDD anode and light radiation combination was advantageous and indicated that the SSPEF process is promising with both a lower cost than using UV lamps and simulating solar photoelectro-Fenton process. The PEF process with the lowest j (100 mA cm−2) showed the best performance-mineralization current efficiency.

Treatment of industrial textile wastewater by the solar photoelectro-Fenton process: Influence of solar radiation and applied current

This work addresses the removal of Acid Blue 29 (AB29) textile dye by a solar photo-electro-Fenton (SPEF) process. Ten liter AB29 solutions containing 100 mg L−1 total organic carbon (TOC), 0.5 mM Fe2+ and 0.05 M Na2SO4 at a pH of 3.0 were electrolyzed by applying current densities of 25 and 50 mA cm−2 in a pilot plant built in our laboratory. The pilot plant was composed of an electrochemical filter press cell with a dimensionally stable anode (DSA-type) and an air-diffusion cathode coupled to a solar photo-reactor.AB29 was completely mineralized by SPEF at the end of electrolysis, while the solution achieved decolorization in short periods of time on sunny days. Reaction intermediates, such as aromatic compounds, carboxylic acids and inorganic ions, were found during the oxidation process. Solar irradiation favors the mineralization of the dye in cost and efficiency compared to other electrochemical methods. Moreover, the treatment of an industrial textile effluent containing AB29 by SPEF produced mineralization greater than 90% on sunny days.

Effect of anodic materials on solar photoelectro-Fenton process using a diazo dye as a model contaminant

Boron-doped diamond (BDD), Pt and Ti/RuO2 anodes were chosen to treat 118 mg L−1 Acid Blue 29 (AB29) solution in 0.050 M Na2SO4 at pH 3.0 by electrochemical oxidation with electrogenerated H2O2 (EO-H2O2), electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) processes. Pseudo-first order decolourisation decays were obtained with the following order of enhancement: EO-H2O2< EF < SPEF. In EO-H2O2 are present the electrogenerated heterogeneous OH radicals on the surface of the anode, while in EF and SPEF, there is the additional influence of homogeneous OH radicals generated in the bulk by Fenton's reaction. In SPEF, the solar radiation enhances catalyst regeneration and OH generation, as well as the photolysis of Fe3+ complexes. Regarding the anodic materials, its effect was less significant in SPEF due to the predominance of homogeneous reactions. In this process, the influence of current density is more meaningful over time than as a function of charge. At the end of 15 min, applying 33.3 mA cm−2, almost complete degradation of AB29 was achieved, regardless of the anode used; 285 min after, complete mineralisation of the organic matter was reached. The energy consumption attained with BDD and Pt was quite similar, ≈ 0.11 kWh gCOD−1, whereas the Ti/RuO2 was 0.09 kWh gCOD−1. Furthermore, the evolution of short-chain carboxylic acids was followed over time and the concentration of nitrogen species was monitored.This study highlights the potential of low cost anode materials to be applied in SPEF in order to achieve a promising and competitive alternative to wastewater treatments.

Influence of electrolysis conditions on the treatment of herbicide bentazon using artificial UVA radiation and sunlight. Identification of oxidation products

The main objective of this work is to demonstrate the viability of solar photoelectro-Fenton (SPEF) process to degrade pesticides in urban wastewater matrix, selecting the herbicide bentazon as a model molecule. In order to provide a correct assessment of the role of the different oxidants and catalysts involved, bentazon was comparatively treated by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and UVA-assisted EF (i.e., PEF) processes as well, either in sulfate or chloride media. Trials were made in a stirred tank reactor with an air-diffusion cathode and a boron-doped diamond (BDD), RuO2-based or Pt anode. In chlorinated matrices, the herbicide disappeared more rapidly using a RuO2-based anode because of the generated active chlorine. The best mineralization performance was always obtained using BDD due to its higher oxidation power, which allowed the complete destruction of refractory chloroderivatives. A concentration of 0.50 mM Fe2+ was found optimal to catalyze Fenton's reaction, largely enhancing the mineralization process under the action of OH. Among photo-assisted treatments, sunlight was proven superior to a UVA lamp to promote the photolysis of intermediates, owing to its greater UV irradiance and contribution of visible photons, although PEF also allowed achieving a large mineralization. In all cases, bentazon decay obeyed a pseudo-first-order kinetics. SPEF treatment in urban wastewater using BDD at only 16.6 mA cm−2 yielded 63.2% mineralization. A thorough, original reaction pathway for bentazon degradation is proposed, including seven non-chlorinated aromatics, sixteen chloroaromatics and two chloroaliphatics identified by GC-MS, most of them not previously reported in literature. Ion-exclusion HPLC allowed the detection of seven short-chain linear carboxylic acids.

Optimization of electrocatalytic H2O2 production at pilot plant scale for solar-assisted water treatment

This manuscript summarizes the successful start-up and operation of a hybrid eco-engineered water treatment system, at pilot scale. The pilot unit, with 100 L capacity, has been devised for the efficient electrocatalytic production of H2O2 at an air-diffusion cathode, triggering the formation of OH from Fenton’s reaction with added Fe2+ catalyst. These radicals, in combination with those formed at a powerful boron-doped diamond (BDD) anode in an undivided cell, are used to degrade a mixture of model pesticides. The capability of the plant to produce H2O2 on site was initially optimized using an experimental design based on central composite design (CCD) coupled with response surface methodology (RSM). This aimed to evaluate the effect of key process parameters like current density (j) and solution pH. The influence of electrolyte concentration as well as liquid and air flow rates on H2O2 electrogeneration and current efficiency at optimized j and pH was also assessed. The best operation conditions resulted in H2O2 mass production rate of 64.9 mg min−1, 89.3% of current efficiency and 0.4 kWh m-3 of energy consumption at short electrolysis time. Performance tests at optimum conditions were carried out with 75 L of a mixture of pesticides (pyrimethanil and methomyl) as a first step towards the elimination of organic contaminants by solar photoelectro-Fenton (SPEF) process. The combined action of homogeneous (OH) and heterogeneous (BDD(OH)) catalysis along with photocatalysis (UV photons collected at a solar CPC photoreactor) allowed the removal of more than 50% of both pesticides in 5 min, confirming the fast regeneration of Fe2+ catalyst through cathodic reduction and photo-Fenton reaction.

Air diffusion electrodes based on synthetized mesoporous carbon for application in amoxicillin degradation by electro-Fenton and solar photo electro-Fenton

The aim of this work was to develop an air diffusion mesoporous carbon electrode (ADE-MC) as cathode for the in-situ electrogeneration of hydrogen peroxide and its application on electro-Fenton (EF) and solar photo electro-Fenton (SPEF) processes. Three different mesoporous carbon materials were obtained by organic-organic self-assembly synthesis (soft-template route) by changing concentrations of resorcinol-formaldehyde polymer as carbon precursor and Pluronic F-127™ surfactant as matrix-forming agent. The materials were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), linear voltammetry (LV) and linear rotating disk electrode voltammetry (LV-RDE). MC materials showed pore diameter between 3.6 and 4.6 nm. The efficiency of ADE-MC was explored as a function of H2O2 produced at current densities (50, 100 and 150 mA cm−2). The highest production of H2O2 was 10.85 mmol L−1 by applying 150 mA cm−2. Finally, the ADE-MC were used for the mineralization of amoxicillin (50 mg L−1), allowing complete degradation and mineralization percentages of 55% and 85% with EF and SPEF processes, respectively. MC electrodes produce H2O2 in enough amounts that provide a viable option to degradation and mineralization of others organic pollutants in aqueous media by EF and SPEF processes.