BDD Anode Research Articles

Study of the electrochemical oxidation of 4,6-dimethyldibenzothiophene on a BDD electrode employing different techniques

• Study of the oxidation steps of 4,6-DMDBT by different techniques using a BDD anode. • 4,6-DMDBT was removed after 60 min of electrolysis at E an = 1.50 V. • Selective oxidation of 4,6-DMDBT to sulfoxide or sulfone. • The conversion depended on concentration, applied potential, and water content. • A small amount of dimers was formed during the electrochemical oxidation. The electrochemical oxidation of 4,6-dimethyldibenzothiophene (4,6-DMDBT) at low concentrations on a BDD anode was investigated in a monophasic acetonitrile (93.5% v/v)–water (6.5% v/v, 0.01 M LiClO 4 ) solution. Two oxidation steps related to the sequential formation of sulfoxide and sulfone derivatives were identified. Kinetic parameters such as the electron transfer coefficient α, the number of electrons n α involved in the rate-determining step, the total number of electrons n , the reaction rate constant k 0 and the diffusion coefficient D of 4,6-DMDBT for the first transformation were determined by cyclic voltammetry, differential pulse voltammetry (DPV), square wave voltammetry and bulk electrolysis under potentiostatic conditions. The process was bielectronic with α = 0.57, n α = 1, k 0 = 7.46 × 10 −6 cm s −1 and D = 2.30 × 10 −6 cm 2 s −1 . DPV was the most sensitive electroanalytical technique. Using 27 mg L −1 of 4,6-DMTDB, DPV allowed determining a conversion of 91% to sulfoxide after 60 min of electrolysis in a BDD/BDD cell at an anodic potential of 1.50 V, with an apparent rate constant of 0.034 min −1 . The electrochemical characterization was corroborated via gas chromatography–mass spectrometry and ultra-high performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry, confirming the formation of the sulfoxide in the first step and the sulfone in the second one as main products, alongside a minor proportion of dimers.

Solid polymer electrolyte as an alternative approach for the electrochemical removal of herbicide from groundwater

Groundwater represents one of the primary freshwater sources, but their pollution is rapidly increasing, and the development of tailored processes is mandatory. In this scenario, electrochemical advanced oxidation processes (EAOPs) represent a promising alternative to face this issue. Their application to groundwater is limited by low electrical conductivity, which directly affects cell voltage and then operating costs. In this paper, three different approaches to overcome this constrain are compared using a BDD anode and a Ti/RuO2 cathode. The first is the addition of a supporting electrolyte as sodium sulfate (Na2SO4); despite its efficacy to increase conductivity, some new problems are introduced in water source management and treatment plant for the electrolyte removal. An alternative approach is the reduction of gap-electrode from 5 mm up to some microns, equivalent to the thickness of a plastic mesh, used to avoid electrodes short-circuit. The third innovative method proposed here is the substitution of insulated mesh with an ionic conductor layer, a solid polymer electrolyte (SPE), like Nafion®117 sandwiched between the electrodes. This modification allows increasing electrochemical performance such as herbicide and COD removal, preserving energy consumptions. Moreover, SPE does not show any performance deterioration in the first 30 h of utilisation. The results suggest that the usage of SPE can be a promising approach for the treatment of groundwater.

Enhanced degradation of contaminants of emerging concern by electrochemically activated peroxymonosulfate: Performance, mechanism, and influencing factors

Electrochemically activated persulfate is an emerging advanced oxidation process for the removal of contaminants of emerging concern (CECs). The degradation of CECs, including carbamazepine (CBZ), bisphenol S (BPS), propranolol (PPL) and sulfamethoxazole (SMX) using electrochemically activated peroxymonosulfate (EA-PMS) was systematically investigated in this work. Over 80% of all the forementioned CECs were removed within 30 min. It exhibited a good synergistic effect between PMS and electrolysis on the degradation of CECs. The results of linear sweep voltammetry (LSV) indicated that a transition structure between BDD anode and PMS (BDD (PMS)*) was likely responsible for the synergistic effect. Hydroxyl radical (HO·) and sulfate radical (SO4·−) were proved to be the primary reactive species, of which HO· played the leading role. The increase of current density and PMS dosage accelerated the degradation of SMX, while initial pH from 3.0 to 11.0 had a limited effect on the degradation of SMX. Moreover, the influences of common ions and natural organic matter (NOM) on the degradation of SMX were comprehensively assessed using response surface methodology (RSM), and a prediction model was built via RSM. The performance of EA-PMS on the degradation of SMX in actual water was even better than that in pure water in this study. EA-PMS can serve as a novel and promising technology for the degradation of CECs and has great potential in practical application.

Treatment of tannery effluent by chemical coagulation combined with batch-recirculated electro-oxidation at different anode materials.

The aim of this work was to evaluate the pollutant load from tannery effluents treated by chemical coagulation (CC) followed by electro-oxidation (EO), performed in two different experimental batch-recirculated setups, one with a BDD anode and the other with Ti/Pt/PbO2 and Ti/Pt/SnO2-Sb2O4 anodes (PS). Results were compared with those obtained from EO of the raw sample. CC was performed with a Fe3+ concentration of 0.25 g L-1, and the applied current densities for EO in each setup were 60 mA cm-2 for BDD and, in the PS setup, 20 and 40 mA cm-2 for Ti/Pt/SnO2-Sb2O4 and Ti/Pt/PbO2, respectively. During CC, removals of 27% in chemical oxygen demand (COD), 14% in total nitrogen, 100% in sulfide, and 73% in Cr(VI) were observed. COD removal in the EO of the raw sample was higher than that obtained for the combined CC + EO, for both setups, showing that the organic compounds removed by CC are mainly those that would be more easily removed by EO. For most of the other parameters related with carbon and nitrogen, the removals for CC + EO were higher than for EO alone. During EO, sulfide is converted to sulfate, especially with BDD. Concerning Cr(VI) concentration, it increases during EO, in particular for PS setup. Combined treatment, with both setups, proved to be an effective choice to treat tannery effluents.

Electrochemical degradation of atrazine by BDD anode: Evidence from compound-specific stable isotope analysis and DFT simulations

Direct charge transfer (DCT) and •OH attack played important roles in contaminant degradation by BDD electrochemical oxidation. Their separate contributions and potential bond-cleavage processes were required but lacking. Here, we carried out promising compound-specific isotope fractionation analysis (CSIA) to explore 13C and 2H isotope fractionation of atrazine (ATZ), followed by assessing the reaction pathway by BDD anode. The correlation of 2H and 13C fractionation allows to remarkably differentiate DCT process and •OH attack, with Λ values of 18.99 and 53.60, respectively. Radical quenching identified that •OH accounted for 79.0%–88.5% in the whole reaction. While CSIA methods provided biased results, which suggested that ATZ degradation exhibited two stages with •OH contributions of 24.6% and 84.3% respectively, confirming CSIA was more sensitive and provided more possibilities to estimate degradation processes. Combined with Fukui index and intermediate products identification, we deduced that dechlorination-hydroxylation mainly occurred in the first 30 min by DCT reaction. While lateral chain oxidation with C–N broken was the governing route once •OH was largely generated, with the production of DEA (m/z 188), DIA (m/z 174), DEIA (m/z 146) and DEIHA (m/z 128). Our results demonstrated that isotope fractionation can offer “isotopic footprints” for identifying the rate-limiting steps and bond breakage process, and opens new avenues for degradation pathways of contaminants.

Electro-oxidation of tetracycline in methanol media on DSA®-Cl2

The electro-oxidation of tetracycline (TeC) in methanol medium containing chloride or sulfate ions was evaluated using a DSA®-Cl2 in a flow reactor and compared with BDD. The results show that after 30 min of electrolysis no TeC is detected by liquid chromatography when chloride is used as supporting electrolyte. On the other hand, after 90 min of electrolysis using a BDD anode only 61% of TeC was removed from solutions with chloride, but in the presence of sulfate the removal reaches 94%. This evidences that the oxidizing species generated during electrochemical oxidation control the process and the mechanism of degradation of the TeC. Besides that, it was possible to infer that only a small amount of methanol might convert to formaldehyde or formic acid, although they were not detected according to the nil changes in the FTIR spectra or in the HPLC chromatograms recorded.

Study of degradation of amitriptyline antidepressant by different electrochemical advanced oxidation processes

Amitriptyline (AMT) is the most widely used tricyclic antidepressant and is classified as a recalcitrant emergent contaminant because it has been detected in different sources of water. Its accumulation in water and soil represents a risk for different living creatures. To remove amitriptyline from wastewater, the Advanced Oxidation Processes (AOPs) stands up as an interesting option since generate highly oxidized species as hydroxyl radicals (OH) by environmentally friendly mechanism. In this work, the oxidation and mineralization of AMT solution have been comparatively studied by 3 Electrochemical AOPs (EAOPs) where the OH is produced by anodic oxidation of H2O (AO-H2O2), or by electro-Fenton (EF) or photoelectro-Fenton (PEF).PEF process with a BDD anode showed the best performance for degradation and mineralization of this drug due to the synergistic action of highly reactive physiosorbed BDD (OH), homogeneous OH and UVA radiation. This process achieved total degradation of AMT at 50 min of electrolysis and 95% of mineralization after 360 min of treatment with 0.5 mmol L−1 Fe2+ at 100 mA cm−2. Six aromatic intermediates for the drug mineralization were identified in short time of electrolysis by GC-MS, including a chloroaromatic by-product formed from the attack of active chlorine. Short-chain carboxylic acids like succinic, malic, oxalic and formic acid were quantified by ion-exclusion HPLC. Furthermore, the formation of NO3− ions was monitored. Finally, the organic intermediates identified by chromatographic techniques were used to propose the reaction sequence for the total mineralization of AMT.

Recent development of electrochemical advanced oxidation of herbicides. A review on its application to wastewater treatment and soil remediation

Herbicides have been largely utilized during the last decades to maintain the quality and quantity of agricultural crop, ensuring the need of an increasing world food production. However, these synthetic organics are highly biorecalcitrant and stable at mild conditions and cannot be effectively destroyed in conventional wastewater treatment facilities. Among the advanced oxidation processes used to remove herbicides, electrochemical technologies have been recently developed at bench scale as potential powerful treatments. This review presents a critical, exhaustive and detailed analysis on the application of single and combined electrochemical advanced oxidation processes to remediate wastewaters and soils contaminated with common herbicides, covering the period 2010–2019. Nine kinds of treatments, including single methods like anodic oxidation, anodic oxidation with electrogenerated H 2 O 2 , homogeneous and heterogeneous electro-Fenton, photoelectro-Fenton, solar photoelectro-Fenton and photoelectrocatalysis, as well as combined ones involving hybrid and sequential processes, have been examined. The fundamentals of each technology are briefly described, and the main results obtained for the removal of the most used herbicide families from synthetic solutions and soil-washing effluents are carefully exposed and discussed. The role of generated oxidizing agents and/or photolytic reactions in photo-assisted processes is explained to justify the mechanisms proposed for herbicide mineralization. The comparative oxidation ability of the different methods is discussed. Finally, future challenges remarking the need of treating real agricultural wastewaters and contaminated soils, the construction of electrochemical systems with stable electrodes at industrial scale and the realization of techno-economic studies are envisaged. • Review of 9 treatments with EAOPs for herbicide removal from wastewaters and soils (2010–2019). • Application of single and combined processes to synthetic herbicide solutions. • Rapid degradation of herbicides and overall mineralization feasible with BDD anodes. • Superiority of SPEF for wastewater treatment due to the positive action of sunlight irradiation. • Better performance for soil-washing effluents remediation by photoelectrolysis with UVC light.

Electro-Fenton Process for the Removal of Direct Red 23 Using BDD Anode in Chloride and Sulfate Media

Electro-Fenton Process for the Removal of Direct Red 23 Using BDD Anode in Chloride and Sulfate Media

Three-dimensional construction of electrode materials using TiC nanoarray substrates for highly efficient electrogeneration of sulfate radicals and molecular hydrogen in a single electrolysis cell

3D nanostructuring strategies for high performance and cost-effective BDD anodes and Pt cathodes have been realized by developing 3D TiC-based substrates.

Treatment of two sartan antihypertensives in water by photo-electro-Fenton using BDD anodes: Degradation kinetics, theoretical analyses, primary transformations and matrix effects

Degradation of two representative antihypertensives, losartan (LOS) and valsartan (VAL) in water by photo-electro-Fenton (PEF), using a BDD anode in presence of sulfate anion was evaluated. PEF showed a fast elimination of these pollutants (>95% at 30 and 60 min of treatment for LOS and VAL, respectively). The main elimination route was the attacks of radicals produced in the system, having pseudo-first-order rate constants of 0.154 and 0.054 min−1 for LOS and VAL, correspondingly. Theoretical analyses of atomic charges were performed to rationalize the antihypertensives reactivity toward the electrogenerated degrading agents. Afterwards, the primary transformation products were assessed. The transformation products revealed that the degrading species attack the biphenyl-tetrazole, imidazole, and alcohol moieties on LOS. Meanwhile, carboxylic and amide groups, plus the central nucleus, were modified on VAL. These moieties corresponded well with the electron-rich sites indicated by the theoretical calculations. Also, the PEF process removed between 33 and 38% of total organic carbon after 5 h of electrolysis. Finally, it was considered LOS treatment in presence of oxalic acid (a typical organic waste of pharmaceutical industry), in addition to the pollutant degradation in effluents from municipal sewage treatment plants by PEF at pH ∼5. Oxalic acid accelerated LOS degradation. Meanwhile, in the effluent, the process led to 64% of LOS removal after 120 min of treatment, indicating the high potentiality of PEF to degrade antihypertensives in water containing organic and inorganic substances.

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.

Performance of electrochemical oxidation over BDD anode for the treatment of different industrial dye-containing wastewater effluents

Abstract This paper presents the results of electrochemical oxidation of dye-containing wastewater over a BDD anode. Batch experiments were conducted at a fixed current density of 2.8 mA/cm2 to analyze the performance of the electrochemical process for the treatment of textile and paint wastewater utilizing different supporting electrolytes (Na2SO4 and NaCl). During electrolysis, emphasis was put on measuring different parameters such as chemical oxygen demand (COD), turbidity, conductivity, and color removal. The results revealed that BDD cell exhibited higher COD removal efficiency for textile wastewater than for paint wastewater. Adding supporting electrolytes had a positive effect on COD, turbidity, and color removal efficiencies for both textile and paint industry effluents. For textile wastewater, Na2SO4 and NaCl yielded a reduction in COD of 94% in 6 hours compared to 84% with no electrolyte added. The presence of Na2SO4 and NaCl in paint wastewater resulted in different COD removal percentages of 71 and 85% respectively with 21% in raw sample after 4 hours of treatment. The discoloration reached a percentage higher than 96% for both effluents and for both electrolytes. Under the same experimental conditions, all cases showed turbidity removal higher than 97%. The kinetic study showed that the reaction rate followed pseudo-first-order kinetics.

Integrated-electrochemical approaches powered by photovoltaic energy for detecting and treating paracetamol in water

Abstract Paracetamol is frequently used as an over-the-counter painkiller and is one of the most commonly consumed pharmaceuticals. Consequently, it is increasingly found in the natural environment, such as the water and soil. For this reason, the monitoring its concentration in water and the treatment of polluted effluents with paracetamol is a key issue to overcome urgently. Then, in this study, an electrochemical measuring device and electrochemical water treatment are integrated for their environmental application on paracetamol control. In the former, raw cork-graphite electrochemical sensor was prepared and a simple differential pulse voltammetric (DPV) method was developed for the quantitative determination of paracetamol. Meanwhile, the degradation of paracetamol was carried out with BDD anode by applying 15, 30, and 60 mA cm−2 and using different electrolyte concentrations of Na2SO4 (25, 50, 75, and 100 mM) over 240 min of treatment, in the latter. The decay and degradation of paracetamol were monitored by DPV, and HPLC measurements. Results indicated that, the electrochemical device exhibited a clear current response, allowing to quantify the analyte in the 2.5–1000 μM range, with limit of detection and quantification of 1.03 μM and 2.44 μM, respectively. Alternatively, BDD-electrolysis demonstrated to be an efficient process for removing organic matter from the pharmaceutical compound effluent via the production of strong oxidizing species. Lower paracetamol concentrations were detected, using the electrochemical sensor, when higher current densities and sulfate concentrations were used in BDD-electrolysis, demonstrating the applicability of integrated-technologies. The evolution of short-carboxylic acids (oxalic, formic, oxamic, maleic, acetic, and glycoxylic) was observed at 60 mA cm−2 and 100 mM of Na2SO4, but all of them were eliminated after 240 min. Inorganic ions (NH4+ and NO3−) were also detected under these experimental conditions, confirming that the pollutant was mineralized. Finally, lower energy requirements were estimated for all experimental conditions; however, solar photovoltaic (PV) renewable energy has been utilized to power these electrochemical technologies, decreasing the investment cost.

Pilot scale continuous reactor for water treatment by electrochemical advanced oxidation processes: Development of a new hydrodynamic/reactive combined model

The development of continuous flow electrochemical reactors is required to overcome the limitations of conventional batch reactors for treatment of large flows of effluents. Therefore, the objective of this study was to develop and characterize a new pilot-scale reactor using BDD anode and carbon felt cathode operating in continuous mode. First, a “Design of Experiment” analysis was performed in order to identify the most critical operating parameters for the percentage of mineralization of 29.8 mg L−1 hydrochlorothiazide (HCT) solution. The liquid flow rate has been identified as the most critical parameter together with the configuration of the reactor (number of electrodes, distance between electrodes). Moreover the designed reactor was able to reach very high percentage of mineralization (97%) for a mean residence time of 83 min. To better understand the important role of the flow rate and the configuration, a hydrodynamic study was then performed. “Residence Time Distribution” curves were obtained and fitted well with the continuous-stirred tank reactor in series with dead zones (CSTR-DZ) model. The 28-electrodes configuration had a lower dead volume fraction whatever the liquid flow rate applied. By increasing the liquid flow rate the hydrodynamic behavior tends more to a plug flow reactor. Finally, a new mathematical model for the mineralization of HCT solution was proposed by combining mineralization kinetic with hydrodynamic CSTR-DZ model. This model was then compared to experimental data and the model was able to capture experimental trends. This approach opens up interesting perspectives for a successful scale-up for continuous electrochemical reactors.

Comparing the electrochemical degradation of the fluoroquinolone antibiotics norfloxacin and ciprofloxacin using distinct electrolytes and a BDD anode: evolution of main oxidation byproducts and toxicity

The effects of the supporting electrolytes (SEs) Na2SO4, NaCl, Na2CO3, NaNO3, and Na3PO4 on the anodic oxidation of norfloxacin (NOR) and ciprofloxacin (CIPRO), assessed by the respective degradation kinetics and byproducts and electrolyzed solution antimicrobial activity, are compared. Galvanostatic anodic oxidations were performed in a filter-press flow cell fitted with a boron-doped diamond anode. Removal rates higher than the theoretical one for a process purely controlled by mass transfer were found for all SEs, indicative of contribution by indirect oxidation processes. However, the removal rates for NaCl were about tenfold higher, with the lowest energy consumption per order (ECO) of targeted pollutant removal rate (ca. 0.7 kW h m–3 order–1), a very competitive performance. The TOC removal rates were also affected by the SE, but not as markedly. The antimicrobial activity of the electrolyzed solutions against Escherichia coli showed distinct temporal profiles, depending on the fluoroquinolone and SE. For instance, when Na3PO4 was used, the antimicrobial activity was completely removed for NOR, but none for CIPRO; conversely, when NaCl was used, complete removal was attained only for CIPRO. From LC-MS/MS analyses of Na3PO4 electrolyzed solutions, rupture of the fluoroquinolone ring leading to byproducts with no toxicity against E. coli occurred only for NOR, whereas exactly the opposite occurred for the NaCl solutions. Clearly, the nature of both the SE and the fluoroquinolone influence the oxidation steps of the respective molecule; this was also evidenced by the distinct short-chain carboxylic acids identified in the degradation of NOR and CIPRO.

Electrochemical removal of Bisphenol A from landfill leachate under Nordic climate conditions

This study investigated the applicability of electrochemical oxidation for landfill leachate treatment in climate areas, where cold temperatures prevail (like Northern Norway). Experiments were completed with pre-treated (coagulation/flocculation and separation) landfill leachate at 6 and 20 °C in order to assess the temperature influence on the degradation of the organic pollutant Bisphenol A and the fate of the ordinary wastewater parameters COD and nitrate. Furthermore, two different anode materials (Ti/Pt and Nb/BDD) and three different current densities (10, 43 and 86 mA cm−2) were compared. Additionally, the formation of the two groups of disinfection by-products, trihalomethanes and perchlorate, was monitored. A 99% removal of Bisphenol A was confirmed at 6 °C on both tested anode materials, but a current density of at least 43 mA cm−2 must be applied. Removal rates were on average 38% slower at 6 °C than at 20 °C. For comparison, Bisphenol A removal in clean electrolyte disclosed faster degradation rates (between 50 and 68%) due to absent landfill leachate matrix effects. The energy consumption for 99% Bisphenol A removal was 0.28 to 1.30 kWh m−3, and was on average 14% higher at 6 °C compared to 20 °C. Trihalomethanes were mainly formed on Pt anodes in the ppb range, while perchlorate was primarily formed at BDD anodes in the ppm range. Formation of disinfection by-products increased with increased applied current and temperature. Electrochemical oxidation was found to be a suitable treatment process for landfill leachate in cold climate areas by successfully meeting treatment goals.Graphic abstract

The generation of hydroxyl radicals and electro-oxidation of diclofenac on Pt-doped SnO2–Sb electrodes

Pt-doped SnO2–Sb electrodes constitute promising candidates for the electrochemical abatement of refractory pollutants, but their efficacy to oxidize emerging pollutants remains uncertain. In this work, the electrochemical oxidation of diclofenac, pharmaceutical pollutant, on Pt-doped Ti/SnO2–Sb electrodes has been studied by cyclic voltammetry and galvanostatic treatment in neutral medium. In parallel, the capability of these anodes to generate hydroxyl radicals (OHs) has been analyzed by in-situ UV spectroelectrochemical measurements. For comparison purposes, the responses of Ti/SnO2–Sb and commercial Ti/Pt and BDD anodes were also evaluated. The voltammetric and electrolysis results show that the different Ti/SnO2–Sb anodes can effectively oxidize and mineralize diclofenac, so their electrochemical activity lies in between that of Ti/Pt and BDD. The incorporation of small amounts of Pt (3–13 at.%) into the SnO2–Sb coatings, despite hindering the OHs generation, enhances the kinetics and efficiency for diclofenac oxidation and mineralization. This better overall response is attributed to a synergy between diclofenac-Pt interaction and efficient OHs generation. Pt-doped Ti/SnO2–Sb electrodes are then presented as a cheaper potential alternative to BDD for treating pharmaceutics pollutants in waters.

A comprehensive study on the electrochemical advanced oxidation of antihypertensive captopril in different cells and aqueous matrices

Anodic oxidation with electrogenerated H2O2 (AO-H2O2) was applied to treat 130 mL of antihypertensive drug captopril in sulfate medium, urban wastewater and synthetic urine using a BDD, Pt or IrO2 anode and an air-diffusion cathode. Oxidants were OH formed during O2 evolution and active chlorine formed via anodic oxidation of Cl−. Drug removal decreased as: BDD > Pt > IrO2. The effect of pH and current density was examined. Further, 2.5 L of drug solutions in the same matrices with Fe2+ at pH 3.0 were treated by solar photoelectro-Fenton (SPEF) using a solar pre-pilot flow plant with a Pt/air-diffusion cell and a planar photoreactor. In sulfate medium, SPEF outperformed AO-H2O2 and electro-Fenton because of the efficient Fe3+ photoreduction. Low mineralization was achieved by the small generation of photoactive Fe(III)-carboxylate complexes. In urban wastewater, captopril was more rapidly removed due to active chlorine. Two heterocyclic derivatives and four aliphatic acids were detected.

Application of electrochemical oxidation in cold climate regions – Effect of temperature, pH and anode material on the degradation of Bisphenol A and the formation of disinfection by-products

Abstract This study assessed the feasibility of electrochemical oxidation (EO) for the removal of organic compounds in cold climate regions. A two-level full factorial design was used to test the effect of three factors, temperature (6/20 °C), anode material (Pt/BDD) and pH (7/10) on the degradation of Bisphenol A. Due to the use of a chloride electrolyte, the formation of the disinfection by-products, perchlorate and trichloromethane was assessed too. The 90 % removal of the initial Bisphenol A concentration took up to 71 % (30 min) longer and up to 46 % more power input was required at 6 °C than at 20 °C. At pH 10, degradation and formation kinetics of Bisphenol A and trichloromethane were faster due to the higher oxidation power of OCl− than HOCl (pKa = 7.5) and the formation of bisphenolate ions (pKa = 9.6), which are more prone to electrophilic attack than Bisphenol A. Temperature and anode material were the two factors that significantly affect the trichloromethane formation. Trichloromethane was formed up to 45 % faster at 20 °C than at 6 °C and up to 23 % faster on Pt than on BDD anodes. However, higher trichloromethane concentration were reached on BDD anodes, but were formed at slower rates. The anode material was the only factor, which had a statistically significant influence on for the formation of perchlorate. On BDD anode up to 89 % more perchlorate was formed than on Pt anode. The present study shows that the application of EO for organic pollutant removal in regions with low average temperatures is a feasible treatment step although it is associated with higher energy demand and consequently higher costs. The formation of unwanted disinfection by-products in chloride containing waters could not be avoided, but it was shown in this study, that it can be limited by an adequate choice of treatment time, pH and anode material.