Air-diffusion Cathode Research Articles

Enhanced mineralization of pharmaceutical residues at circumneutral pH by heterogeneous electro-Fenton-like process with Cu/C catalyst

Conventional electro-Fenton (EF) process at acidic pH ∼3 is recognized as a highly effective strategy to degrade organic pollutants; however, homogeneous metal catalysts cannot be employed in more alkaline media. To overcome this limitation, pyrolytic derivatives from metal-organic frameworks (MOFs) have emerged as promising heterogeneous catalysts. Cu-based MOFs were prepared using trimesic acid as the organic ligand and different pyrolysis conditions, yielding a set of nano-Cu/C catalysts that were analyzed by conventional methods. Among them, XPS revealed the surface of the Cu/C-A2-Ar/H2 catalyst was slightly oxidized to Cu(I) and, combined with XRD and HRTEM data, it can be concluded that the catalyst presents a core-shell structure where metallic copper is embedded in a carbon layer. The antihistamine diphenhydramine (DPH), spiked into either synthetic Na2SO4 solutions or actual urban wastewater, was treated in an undivided electrolytic cell equipped with a DSA-Cl2 anode and a commercial air-diffusion cathode able to electrogenerate H2O2. Using Cu/C as suspended catalyst, DPH was completely degraded in both media at pH 6–8, outperforming the EF process with Fe2+ catalyst at pH 3 in terms of degradation rate and mineralization degree thanks to the absence of refractory Fe(III)-carboxylate complexes that typically decelerate the TOC abatement. From the by-products detected by GC/MS, a reaction sequence for DPH mineralization is proposed.

Efficient H2O2 Production and Activation by Air Diffusion Cathode Combined with Ultraviolet for Lake Water Treatment: A Long-Term Evaluation

This study utilizes a natural air diffusion cathode (ADC) and an ultraviolet lamp to construct a UV/H2O2 reactor for the in situ synthesis and activation of H2O2 and evaluates its potential application in practical lake water treatment. The results indicate that the reactor exhibits stable treatment performance during a continuous flow experiment of 80 h. The air diffusion cathode maintains an H2O2 concentration of above 350 mg·L−1 in sodium sulfate electrolyte and shows no decreasing trend. Under the condition of approximately 59% H2O2 utilization, the removal rates of COD and TOC are 37.6% and 40.0%, respectively; the rate of reduction of A254 is 64.3%; while the total bacterial count removal rate reaches 100%. Large organic molecules in surface water are degraded to small organic molecules and mineralized to inorganic minor molecules. It effectively ameliorates the problem of organic pollution of surface water and effectively kills bacteria and improves the microbiological safety of the water body. Therefore, the UV/H2O2 system developed in this study, based on electrochemically produced H2O2, is an effective method for treating micro-polluted surface water.

Novel photoelectrocatalytic system of oxygen vacancy-rich black TiO2-x nanocones photoanode and natural air diffusion cathode for efficient water purification and simultaneous H2O2 production

Photoelectrocatalytic (PEC) system harnesses solar energy for chemical reactions, representing a highly promising renewable energy-based technology for water purification. Herein, we design a novel separated PEC system that integrates water purification on an oxygen vacancy-rich black TiO2 nanocones (b-TiO2-x) photoanode with two-electron O2 reduction reaction for H2O2 production on a natural air diffusion cathode. This integration benefits from thermodynamic advantages, synergy effects and enhanced •OH production, thus exhibiting superior water purification (98.32%, 0.064 min−1) and H2O2 production (6.83 μmol/h/cm2) at ultra-low applied cell voltage of 0.5 V, with the energy consumption of only 0.034 kWh/m3 wastewater treated, where the simultaneous production of value-added H2O2 could fully compensate for the electric cost of the system. Notably, even under real sunlight irradiation, this system achieves efficient water purification and H2O2 production without additional energy consumption, offering a cost-effective and environmental-benign strategy for the dual purpose of water purification and resourcization.

Sequential use of a continuous-flow electrocoagulation reactor and a (photo)electro-Fenton recirculation system for the treatment of Acid Brown 14 diazo dye

The decolorization and TOC removal of solutions of Acid Brown 14 (AB14) diazo dye containing 50 mg L−1 of total organic carbon (TOC) have been first studied in a continuous-flow electrocoagulation (EC) reactor of 3 L capacity with Fe electrodes of ∼110 cm2 area each. Total loss of color with poor TOC removal was found in chloride, sulfate, and/or hydrogen carbonate matrices after 18 min of this treatment. The best performance was found using 5 anodes and 4 cathodes of Fe at 13.70 A and low liquid flow rate of 10 L h−1, in aerated 39.6 mM NaCl medium within a pH range of 4.0–10.0. The effluent obtained from EC was further treated by electro-Fenton (EF) using a 2.5 L pre-pilot flow plant, which was equipped with a filter-press cell comprising a Pt anode and an air-diffusion cathode for H2O2 electrogeneration. Operating with 0.10–1.0 mM Fe2+ as catalyst at pH 3.0 and 50 mA cm−2, a similar TOC removal of 68 % was found as maximal in chloride and sulfate media using the sequential EC-EF process. The EC-treated solutions were also treated by photoelectro-Fenton (PEF) employing a photoreactor with a 125 W UVA lamp. The sequential EC-PEF process yielded a much higher TOC reduction, close to 90 % and 97 % in chloride and sulfate media, respectively, due to the rapid photolysis of the final Fe(III)-carboxylate complexes. The formation of recalcitrant chloroderivatives from generated active chlorine limited the mineralization in the chloride matrix. For practical applications of this two-step technology, the high energy consumption of the UVA lamp in PEF could be reduced by using free sunlight.

Efficient wastewater treatment in petroleum refineries: Hybrid electro-fenton and photocatalysis (UV/ZnO) process

In this study, a new hybrid system composed of a photo-catalysis (UV/ZnO) process combined with an electro-Fenton (EF) process equipped with a micro porous graphite air diffusion cathode (MPGADC) was used to treat petroleum refinery wastewater (PRW). The hybrid system was operated in a batch recycle mode and its performance was investigated and optimized using a response surface methodology (RSM). Three operating parameters affecting on the removal efficiency (RE%) of chemical oxygen demand (COD) were investigated including current density (2–10 mA/cm2), ZnO dosage (0.05–0.35 g/L), and Fe2+concentration (0.05–0.15 mM). Results showed that the optimum operating conditions can be achieved using a current density of 6.44 mA/cm2, with ZnO dosage of 0.35 g/L, and concentration of Fe2+ ions at 0.05 mM in which RE% of 90.15% was obtained with requiring a total electrical energy consumption (EECT) of 19.102KWh/m3. Furthermore, analysis of variance (ANOVA) exhibited a high value of determination coefficient (R2) close to 98.24% indicating a satisfactory fit between the obtained regression model and the experimental results. Moreover, ANOVA results revealed that current density has the most significant effect on RE% with a contribution of 52.41% followed by ZnO dosage and Fe2+ concentration both of them with a contribution of 11.64%. The comparison between the individual photo-catalysis process and hybrid process showed that RE% increases from 77.83% to 90.15% making an enhancement by 15.83% in RE% while EECT decreased from 27.171to 19.102KWh/m3 making a reduction by 29.7% in EECT. Hence, combining EF with photo-catalysis process improves the efficiency and reduced the required energy in comparison with the individual photo-catalysis process. Therefore, the combined process could be considered as an alternative, sustainable, green and cost-effective method for treatment of refinery wastewaters.

Petroleum refinery wastewater treatment using a novel combined electro-Fenton and photocatalytic process

In the current study, treatment of petroleum refinery wastewater has been successfully achieved using a novel photocatalysis-ElectroFenton system operated at a batch circulation mode and composed from a tubular electro-Fenton reactor provided with a macro-porous graphite air diffusion cathode (MPGADC) combined with a new configuration of photo reactor. The feasibility of the combined electro-Fenton with photo-catalytic process (EF + UV/ TiO2) was evaluated using response surface methodology (RSM) with Box-Behnken design (BBD). Titanium dioxide (Anatase) was used as a photo-catalyst and characterized by x-ray diffractometer (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller surface area (BET). Four main operating variables were studied: current density (5–15 mA/cm2, Fe2+concentration (0.1–0.5 mM), TiO2 dosage (0.1–0.7 g/l), and reaction time (20–60 min). Results revealed that reaction time has the most effective parameter on the EF + UV/ TiO2 process followed by TiO2 dosage, Fe2+concentration, and current density. The optimum operating conditions for maximizing COD removal (RE%) and minimizing the total electrical energy consumption (EECT)) were found to be a current density of 15 mA/cm2, Fe2+ concentration of 0.5 mM, TiO2 dosage of 0.7 g/l, and a reaction time of 54 min in which COD removal of 91.26 % was achieved with claiming EECT of 26.86 kWh/m3. Results revealed a vital improvement of using EF + UV/ TiO2 in comparison with UV/ TiO2 alone where an enhancement of 23% in RE% and a reduction by 55% of EECT were observed. Furthermore, a kinetic study was performed for EF + UV/TiO2 and UV/ TiO2 alone in which the results revealed that decay of COD obeyed a pseudo-first-order kinetic for the two processes with a high-rate constant for EF + UV/ TiO2 process.

Carbon spheres modified titanium air diffusion cathode for boosting H2O2 and application in disinfection

In situ electrochemical disinfection via H2O2 through two-electron molecular oxygen reduction reaction (2e-ORR) represents a promising strategy for sustainable disinfection. However, its disinfection performance is largely confined by its low selectivity/reactivity towards two-electron oxygen reduction reaction (2e-ORR) for H2O2 production. To tackle this, carbon spheres modified tubular titanium air diffusion cathode (CS@TTC) was developed. It intended to improve interfacial structures for high H2O2 production through a facile hydrothermal carbonation approach. Evolution of morphology and chemical nature of carbon spheres have been systemically investigated under diverse hydrothermal temperature, hydrothermal time and pyrolysis temperature·H2O2 accumulation has improved 6.59-fold at CS@TTC compared to the raw base TTC. Both chemical nature of carbon sphere and a superior oxygen mass transfer (0.0284 s−1) were responsible for this enhancement. Besides, CS@TTC cathode was used in the electrochemical system for disinfection performance, in which 6.42 log of E. coli was deactivated after 120 min. Hence, this study gives an insight into that the H2O2-based electrochemical disinfection is promising to be a next-generation process.

Treatment of petroleum refinery wastewater by electrofenton process using a low cost porous graphite air-diffusion cathode with a novel design

A low-cost micro porous graphite air diffusion cathode (MPGADC) has been utilized successfully for the in-situ hydrogen peroxide generation via O2 reduction in 0.05 M Na2SO4. Using a tubular electrochemical reactor with a novel design composed of MPGADC as a cathode and a hollow cylinder porous graphite as an anode, a maximum of 68 mg/ L of H2O2 was produced at a current density of 25 mA/cm2, an air flow rate of 3 L/min, and a pH value of 3. Electro-Fenton (EF) process was adopted to remove the chemical oxygen demand (COD) from the wastewater of Al-Dora petroleum refinery in Iraq using this new style of tubular electrochemical reactor. Based on the response surface methodology (RSM) with Box-Behnken design (BBD), the effect of EF operating parameters on the COD removal was investigated.The optimal conditions for maximizing COD removal efficiency (RE%) with lowering specific energy consumption (SEC) using EF process were determined to be a current density of 6.66 mA/cm2, Fe2+ concentration of 0.80 mM, and an electrolysis duration of 60 min, in which RE% of 94% with SEC of 3.75 kWh/kg COD were achieved. In addition, the results demonstrated that the current density has the greatest influence on the COD removal, followed by electrolysis duration and then Fe2+ concentration. Furthermore, current density has the greatest impact on the specific energy consumption, followed by time, while Fe2+ concentration has a negligible effect. The high R2 value (98.33%) confirmed the goodness of fitting the model equation. These results established the viability of employing the new cathode design for the EF process in treatment of petroleum refinery wastewaters.

Generation of hydroxyl radicals in the peroxi-coagulation process with an air-diffusion cathode: Fluorescence analysis and kinetic modeling

Conventional peroxi-coagulation process is based on the combined occurrence of electrocoagulation and oxidation in a single unit, since H2O2 and Fe2+ are electrogenerated on site from cathodic and anodic reactions, respectively. The present work aims to evaluate the effect of pH and applied current on the generation of hydroxyl radicals (•OH) from Fenton’s reaction during peroxi-coagulation treatment. The electrochemical cell consisted of a gas-diffusion cathode with graphite cloth, and an iron plate anode. By using a fluorescence probe (coumarin) and kinetic modeling, it has been possible to estimate the •OH concentration at different current values and to determine the effect of pH on their production. A system with six ordinary differential equations was established and solved to predict the concentrations of the main species of Fenton’s reaction. In addition, the interference of possible by-products and side coumarin hydroxylation reactions in the determination of •OH was considered. The simulation results reveal that current increase from 10 to 50 mA positively influences the •OH generation, further decreasing when operating at 70 mA. This is attributed to: (i) the negative effect of an excessive H2O2 generation, and (ii) the increase in pH during the electrolysis. This latter phenomenon is detrimental because of the partial precipitation of Fe2+ catalyst. A sensitivity analysis was performed to determine the most influential kinetic constants of the model on •OH and 7-hydroxycoumarin concentrations. This work demonstrates the importance of considering possible side reactions, which may occur when coumarin is used as a probe compound to quantify the •OH.

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.

Singlet oxygen generation for selective oxidation of emerging pollutants in a flow-by electrochemical system based on natural air diffusion cathode.

The decay of free radicals involved in side reactions is one of the challenges faced by electrochemical degradation of organic pollutants. To this end, a non-radical oxidation system was constructed by a natural air diffusion cathode (ADC) and a Ti-based dimensional stable anode coated by RuO2 (RuO2-Ti anode) for cathodic hydrogen peroxide activation by anodic chlorine evolution. The ADC fabricated by the carbon black of BP2000 produced a stable concentration of hydrogen peroxide of 339.94mg L-1 (current efficiency of 73.4%) without aeration, which was superior to the cathode made by the XC72 carbon black. The flow-by ADC-RuO2 system consisted of an ADC and a RuO2-Ti anode showed high selectivity to aniline (AN) compared to benzoate (BA) in a NaCl electrolyte, whose degradation efficiencies were 97.72% and 1.3%, respectively. Rapid degradations of a mixture of emerging pollutants and AN were also observed in the ADC-RuO2 system, with pseudo-first-order kinetic constants of 0.51, 1.29, 0.89, and 0.99min-1 for Bisphenol A (BPA), tetracycline (TC), sulfamethoxazole (SMX) and AN, respectively. Quenching experiments revealed the main reactive oxygen species for the pollutant degradation was singlet oxygen (1O2), which was also identified by the electron spin resonance (ESR) analysis. Finally, the steady-stable content of 1O2 was quantitatively determined to be 6.25 × 10-11M by the method of furfuryl alcohol (FFA) probe. Our findings provide a fast, low energy consumption and well controlled electrochemical oxidation method for selective degradation of organic pollutants. H2O2 generated on an air diffusion cathode by naturally diffused O2, reacts with ClO- produced from chloride oxidation on the RuO2-Ti anode to form singlet oxygen (1O2). The electrochemical system shows an efficient oxidation to electron-rich emerging pollutants including bisphenol A, tetracycline, sulfamethoxazole and aniline, but a poor performance on the electron-deficient compounds (e.g., benzoate).

Energy-Efficient H2O2 Electro-production Based on an Integrated Natural Air-Diffusion Cathode and Its Application

Given the low oxygen mass transfer rate and high aeration energy consumption, the traditional two-electron oxygen reduction reaction (ORR) is restricted. In this study, the integrated natural air diffusion cathode (INAC) and a reactor configuration with the horizontal scale facing to air (FTA) demonstrated highly selective H2O2 production for the removal of organic contaminants. Simply synthesized by shaping the mixture of carbon black and polytetrafluoroethylene, the INAC exhibited not only massive pores in all directions for sufficient mass transfer but also the integrated configuration for low charge transfer resistance. Based on the oxygen mass transfer models, for the ORR reaction kinetics, the interface oxygen concentration index was higher than 40, contributing to the high current efficiency of H2O2 production (>90%). The oxygen diffusion model can provide the quantitative description of H2O2 synthesis for porous electrode optimized design. Combining the INAC with the reactor configuration with the FTA mode for free additional O2/air source supply, the electrical efficiency per order was lower than 0.14 kWh m–3, and the removal rate of sulfonamides per unit current could reach 11 mg min–1 A–1, reaching the best reports. This ultraefficient process equipped with the INAC and the FTA mode provides a meaningful practical application prospect for wastewater treatment.

Efficient treatment for tannery wastewater through sequential electro-Fenton and electrocoagulation processes

This work aims to study the ability of using single and sequential electro-Fenton (EF) and electrocoagulation (EC) processes in order to treat tannery wastewater. The first method (EF) was run with an air diffusion cathode for H2O2 generation and boron–doped diamond (BDD) as an anode. The second method (EC) was conducted with mild steel electrodes. The applied processes' performance was monitored by the removals of chemical oxygen demand (COD) along with the total Cr in addition to the electric energy consumption (EEC). To achieve the allowable discharge limits in aquatic media, a hybrid 2 h EF-5 h EC process was applied to treat tannery wastewater, based on the optimization results of every single method, achieving (88.1 ± 4.8)% COD removal rate with total elimination of Cr. In addition, the results of other parameters evolution such as pH, turbidity and the concentration of ions were discussed. As a result, the global EEC of the hybrid treatment was reduced to about 1.7 times. Finally, precipitate and sludge generated at the end of each treatment were examined by X-Ray Diffraction (XRD) analysis to determine their crystalline structure for valorization or reuse possibilities.

An efficient simultaneous degradation of sulfamethoxazole and trimethoprim by photoelectro-Fenton process under non-modified pH using a natural citric acid source: study of biodegradability, ecotoxicity, and antibacterial activity.

In this work, the use of natural organic wastes (orange and lemon peels) as sources of citric acid was evaluated along with the application of the photoelectro-Fenton (PEF) system under non-modified pH as a novel alternative to degrade a complex mixture of pharmaceuticals: sulfamethoxazole (SMX-7.90 × 10-5mol/L) and trimethoprim (TMP-6.89 × 10-5mol/L). The system was equipped with a carbon felt air diffusion cathode (GDE) and a Ti/IrO2 anode doped with SnO2 (DSA). A 3.6 × 10-5mol/L solution of commercial citric acid was used as a reference. The pharmaceuticals' evolution in the mixture was followed by high-performance liquid chromatography (HPLC). The addition of natural products showed an efficient simultaneous degradation of the antibiotics (100% of SMX and TMP at 45min and 90min, respectively) similar to the performance produced by adding the commercial citric acid to the PEF system. Moreover, the addition of natural products allowed for an increment of biodegradability (100% removal of TOC by a modified Zahn Wellens test) and a decrease in ecotoxicity (0% in the bioassay with D. Magna) of the treated solutions. The antibacterial activity was eliminated after only 45min of treatment, suggesting that the degradation by-products do not represent a significant risk to human health or the environment in general. Results suggest that, because of the efficient formation of Fe-citrate complexes, the PEF could be enhanced by the addition of natural organic wastes as a sustainable alternative ecological system for water contaminated pharmaceuticals. Additionally, the potential of reusing natural organic wastes has been exposed, contributing to an improved low-cost PEF by decreasing the environmental contamination produced by this type of waste.

Efficient hydrogen peroxide production at high current density by air diffusion cathode based on pristine carbon black

• Air diffusion cathode is fabricated with Black Pearls 2000a by rolling method. • The catalyst layer contain abundant surface C C=O groups. • Current efficiency of >90% achieved at current density of up to 151 mA cm −2. • The cathode exhibits good applicability at the pH range of 1–13. H 2 O 2 production through electrochemical 2-electron reduction of oxygen (O 2 ) is a promising route whereas the faradaic efficiency is generally limited under high current density. In this work, a three-layer air diffusion cathode (ADC) is fabricated with carbon black (CB, black pearls 2000) and PTFE by rolling method. On account of the porous surface with dominant meso and micro pores, high hydrophobic and abundant surface C O groups, the ADC exhibits H 2 O 2 yield of 85.2 ± 0.5 mg cm -2 h −1 , and current efficiency (CE) of 90.6 ± 0.4 % at 151 mA cm −2 during a 20-cycle operation. Further elevating the current density to 301 mA cm −2 results in H 2 O 2 yield of up to 119.4 mg cm -2 h −1 while CE dropped to 62.3 %. In addition, efficient H 2 O 2 yields are achieved at wide pH range of 1.0–13.0. The applicability and stability of the ADC indicate its great potential for electrosynthesis of H 2 O 2 and electrochemical advanced oxidation processes at practical scales.

An electrochemical advanced oxidation process for the treatment of urban stormwater

Recharge of urban stormwater has often been limited by the high cost of land and concerns about contamination of groundwater. To provide a possible solution, we developed an electrochemical advanced oxidation system (UV/H2O2) that is compatible with high-capacity stormwater recharge systems (e.g., drywells). The system employed an air-diffusion cathode to generate a H2O2 stock solution (i.e., typically around 600 mM) prior to the storm event. The H2O2 stock solution was then metered into stormwater and converted into hydroxyl radical (•OH) by an ultraviolet lamp. The energy consumption for H2O2 generation was optimized by adjusting the applied current density and adding an inert salt (e.g., Na2SO4) to stormwater. H2O2 in the stock solution was unstable. By mixing the basic H2O2 containing catholyte and the acidic anolyte, the stability increased, enabling generation of the H2O2 stock solution up to three days prior the storm event with loss of less than 20% of the H2O2. Lab-scale experiments and a kinetic model were used to assess the feasibility of the full-scale advanced oxidation system. System performance decreased at elevated concentrations of dissolved organic carbon in stormwater, due to enhanced light reflection and backscattering at the water-air interface in the UV reactor, competition for UV light absorption with H2O2 and the tendency of organic matter to act as a •OH scavenger. The proposed system can be incorporated into drywells to remove greater than 90% of trace organic contaminants under typical operating conditions. The electrical energy per order of the system is estimated to range from 0.5 to 2 kWh/m3, depending on the dissolved organic carbon concentration.

Degradation of desphenyl chloridazon in a novel synergetic electrocatalytic system with Ni–Sb–SnO2/Ti anode and PEDOT/PSS-CNTs modified air diffusion cathode

This study explored the depth treatment of desphenly chloridazon (DPC) wastewater by a novel synergetic dual-electrodes electrocatalytic (SDEs) system which consisted of Ni–Sb–SnO2/Ti anode (NSSTA) and PEDOT/PSS-CNTs modified activated carbon air diffusion cathode (PP-CNTs AC ADC). NSSTA exhibited an enhanced capability to produce reactive oxygen species (·OH and O3), its O3 production increased to 6.54 mg/L. PP-CNTs AC ADC was observed to have improved activity of catalyzing oxygen reduction reaction (ORR) with 648.23 mg/L H2O2 generated. Owing to the synergetic effect of O3 and H2O2, additional ·OH was obtained in SDEs system through the electro-peroxone reaction. Compared with the single-electrode electrocatalytic (SE) systems, the SDEs system showed superior pesticide degradation performance, higher mineralization current efficiency (MCE) and lower energy consumption (EC). In the SDEs system, the optimal 91.7% of DPC removal efficiency and 90.7% of DPC mineralization efficiency were obtained within 150 min by electrocatalytic oxidation of 17.5 ppm and 25 ppm pesticide wastewater at the current density of 11.94 mA/cm2, respectively. The treated water showed reduced acute toxicity than that of the raw wastewater, which suggested that the SDEs system is a promising technology for depth treatment of the pesticide industry effluent with simultaneous decontamination and detoxification realized.

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.

Mineralization of the antibiotic levofloxacin by the electro-peroxone process using a filter-press flow cell with a 3D air-diffusion electrode

This paper concerns the degradation of the antibiotic levofloxacin (LVN) by the electro-peroxone (E-peroxone) process in a lab-scale flow plant operated in recirculation mode. The flow plant consists of a filter-press type electrolyzer, the ECO-cell, equipped with a Ti|IrSnSb-oxides plate as anode, and a 3D air-diffusion cathode (graphite felt + carbon cloth-PTFE), where hydrogen peroxide (H2O2) is generated by the oxygen reduction reaction (ORR). The ozone (O3) gas, externally produced, was injected directly into the electrolyte flow pipeline to favor the mixing of O3 + H2O2 and thus promote the formation of hydroxyl radicals (OH) to mineralize LVN. The influence of current density (j), volumetric electrolyte flow rate (Q), and initial concentration of LVN on the mineralization efficiency was systematically analyzed. The best E-peroxone trial achieved 63% mineralization of LVN (initially having 20 mg L−1 TOC in 0.05 M Na2SO4 at pH 3), with current efficiency and electrolytic energy consumption of 9.2% and 0.27 kWh (gTOC)−1, respectively, for the electrolysis performed at j = 20 mA cm−2 and Q = 2.0 L min−1. The processes of ozonation and anodic oxidation with simultaneous formation of H2O2 (AO-H2O2) were also performed and compared with the E-peroxone method. Oxalic, oxamic, and tartaric acids were determined throughout the electrolysis and identified as the main final products of LVN mineralization.

Simultaneous persulfate activation by electrogenerated H2O2 and anodic oxidation at a boron-doped diamond anode for the treatment of dye solutions

The development of new or upgraded electrochemical water treatment technologies is considered a topic of great interest. Here, Tartrazine azo dye solutions were treated by means of a quite innovative dual electrochemical persulfate (S2O82−, PS) activation that combines H2O2 generation at an air-diffusion cathode and anodic oxidation (AO) at a boron-doped diamond (BDD) anode using a stirred tank reactor. This so-called AO-H2O2/PS process was compared to AO with stainless steel cathode, both in 50 mM Na2SO4 medium, finding the oxidation power increasing as: AO < AO-H2O2 < AO/PS < AO-H2O2/PS. In the latter, the dye and its products were mainly destroyed by: (i) hydroxyl radicals, formed either from water oxidation at BDD surface or via reaction between H2O2 and S2O82−, and (ii) sulfate radical anion, formed from the latter reaction, thermal PS activation and cathodic S2O82− reduction. Hydroxyl radicals prevailed as oxidizing agents, as deduced from trials with tert-butanol and methanol. The reaction between S2O82− and accumulated H2O2 was favored as temperature increased from 25 to 45 °C. The effect of PS content up to 36 mM, dye concentration within the range 0.22–0.88 mM, current density (j) between 8.3 and 33.3 mA cm−2 and pH between 3.0 and 9.0 on the process performance was examined. All decolorization profiles agreed with a pseudo-first-order kinetics. The best results for treating 0.44 mM dye were attained with 36 mM PS at pH 3.0, j = 16.7 mA cm−2 and 45 °C, yielding total loss of color, 62% TOC removal and 50% mineralization current efficiency after 360 min. The slow mineralization was attributed to the persistence of recalcitrant byproducts like maleic, acetic, oxalic, formic and oxamic acids. It is concluded that the novel AO-H2O2/PS process is more effective than AO/PS to treat Tartrazine solutions, being advisable to extend the study to other organic pollutants.