Electrochemical degradation of the β-blocker metoprolol by Ti/Ru 0.7 Ir 0.3 O 2 and Ti/SnO 2-Sb electrodes

Trace Br- Inhibits Halogenated Byproduct Formation in Saline Wastewater Electrochemical Treatment

The electrochemical technology provides a practical and viable solution to the global water scarcity issue, but it has an inherent challenge of generating toxic halogenated byproducts in treatment of saline wastewater. Our study reveals an unexpected discovery: the presence of a trace amount of Br- not only enhanced the electrochemical oxidation of organic compounds with electron-rich groups but also significantly reduced the formation of halogenated byproducts. For example, in the presence of 20 μM Br-, the oxidation rate of phenol increased from 0.156 to 0.563 min-1, and the concentration of total organic halogen decreased from 59.2 to 8.6 μM. Through probe experiments, direct electron transfer and HO• were ruled out as major contributors; transient absorption spectroscopy (TAS) and computational kinetic models revealed that trace Br- triggers a shift in the dominant reactive species from Cl2•- to Br2•-, which plays a key role in pollutant removal. Both TAS and electron paramagnetic resonance identified signals unique to the phenoxyl and carbon-centered radicals in the Br2•--dominated system, indicating distinct reaction mechanisms compared to those involving Cl2•-. Kinetic isotope experiments and density functional theory calculations confirmed that the interaction between Br2•- and phenolic pollutants follows a hydrogen atom abstraction pathway, whereas Cl2•- predominantly engages pollutants through radical adduct formation. These insights significantly enhance our understanding of bromine radical-involved oxidation processes and have crucial implications for optimizing electrochemical treatment systems for saline wastewater.

A combined experimental and computational approach to unravel degradation mechanisms in electrochemical wastewater treatment

Electrochemical wastewater treatment is a promising technique to remove recalcitrant pollutants from wastewater. However, the complexity of elucidating the underlying degradation mechanisms hinders its optimisation not only from a techno-economic perspective, as it is desirable to maximise removal efficiencies at low energy and chemical requirements, but also in environmental terms, as the generation of toxic by-products is an ongoing challenge. In this work, we propose a novel combined experimental and computational approach to (i) estimate the contribution of radical and non-radical mechanisms as well as their synergistic effects during electrochemical oxidation and (ii) identify the optimal conditions that promote specific degradation pathways. As a case study, the distribution of the degradation mechanisms involved in the removal of benzoic acid (BA) via boron-doped diamond (BDD) anodes was elucidated and analysed as a function of several operating parameters, i.e., the initial sulfate and nitrate content of the wastewater and the current applied. Subsequently, a multivariate optimisation study was conducted, where the influence of the electrode nature was investigated for two commercial BDD electrodes and a customised silver-decorated BDD electrode. Optimal conditions were identified for each degradation mechanism as well as for the overall BA degradation rate constant. BDD selection was found to be the most influential factor favouring any mechanism (i.e., 52-85% contribution), given that properties such as its boron doping and the presence of electrodeposited silver could dramatically affect the reactions taking place. In particular, decorating the BDD surface with silver microparticles significantly enhanced BA degradation via sulfate radicals, whereas direct oxidation, reactive oxygen species and radical synergistic effects were promoted when using a commercial BDD material with higher boron content and on a silicon substrate. Consequently, by simplifying the identification and quantification of underlying mechanisms, our approach facilitates the elucidation of the most suitable degradation route for a given electrochemical wastewater treatment together with its optimal operating conditions.

A Review of PFAS Destruction Technologies

Per- and polyfluoroalkyl substances (PFASs) are a family of highly toxic emerging contaminants that have caught the attention of both the public and private sectors due to their adverse health impacts on society. The scientific community has been laboriously working on two fronts: (1) adapting already existing and effective technologies in destroying organic contaminants for PFAS remediation and (2) developing new technologies to remediate PFAS. A common characteristic in both areas is the separation/removal of PFASs from other contaminants or media, followed by destruction. The widely adopted separation technologies can remove PFASs from being in contact with humans; however, they remain in the environment and continue to pose health risks. On the other hand, the destructive technologies discussed here can effectively destroy PFAS compounds and fully address society's urgent need to remediate this harmful family of chemical compounds. This review reports and compare widely accepted as well as emerging PFAS destruction technologies. Some of the technologies presented in this review are still under development at the lab scale, while others have already been tested in the field.

Formation of chlorate and perchlorate during electrochemical oxidation by Magnéli phase Ti4O7 anode: inhibitory effects of coexisting constituents

Formation of chlorate (ClO₃⁻) and perchlorate (ClO₄⁻) as by-products in electrooxidation process has raised concern. In the present study, the formation of ClO₃⁻ and ClO₄⁻ in the presence of 1.0 mM Cl⁻ on boron doped diamond (BDD) and Magneli phase titanium suboxide (Ti₄O₇) anodes were evaluated. The Cl⁻ was transformed to ClO₃⁻ (temporal maximum 276.2 μM) in the first 0.5 h on BDD anodes with a constant current density of 10 mA cm², while approximately 1000 μM ClO₄⁻ was formed after 4.0 h. The formation of ClO₃⁻ on the Ti₄O₇ anode was slower, reaching a temporary maximum of approximately 350.6 μM in 4.0 h, and the formation of ClO₄⁻ was also slower on the Ti₄O₇ anode, taking 8.0 h to reach 780.0 μM. Compared with the BDD anode, the rate of ClO₃⁻ and ClO₄⁻ formation on the Ti₄O₇ anode were always slower, regardless of the supporting electrolytes used in the experiments, including Na₂SO₄, NaNO₃, Na₂B₄O₇, and Na₂HPO₄. It is interesting that the formation of ClO₄⁻ during electrooxidation was largely mitigated or even eliminated, when methanol, KI, and H₂O₂ were included in the reaction solutions. The mechanism of the inhibition on Cl⁻ transformation by electrooxidation was explored.

Direct and Indirect Electrooxidation of Glycerol to Value-Added Products

In this work, different approaches for the direct and indirect electrooxidation of glycerol, a by-product of oleochemistry and biodiesel production, for the synthesis of value-added products and of intermediates for biofuel/electrofuel production, were investigated and compared. For the direct electrooxidation, metallic catalysts were used, whose surfaces were modified by promoters or second catalysts. Bi-modified Pt electrodes (Pt_x Bi_y /C) served as model systems for promoter-supported electrocatalysis, whereas IrO₂ -modified RuO₂ electrodes were studied as catalyst combinations, which were compared under acidic conditions with the respective monometallic catalysts (Pt/C, RuO₂ /Ti, IrO₂ /Ti). Furthermore, inorganic halide mediators (chloride, bromide, iodide) and organic nitroxyl mediators (4-oxo-2,2,6,6-tetramethyl-piperidin-1-oxyl and 4-acetamido-2,2,6,6-tetramethyl-piperidin-1-oxyl) were evaluated for indirect electrooxidation. These different approaches were discussed regarding selectivity, conversion, and coulombic efficiency of the electrochemical glycerol oxidation.

Graphene-based sponges for electrochemical degradation of persistent organic contaminants

Graphene-based sponges doped with atomic nitrogen and boron were applied for the electrochemical degradation of persistent organic contaminants in one-pass, flow-through mode, and in a low-conductivity supporting electrolyte. The B-doped anode and N-doped cathode was capable of >90% contaminant removal at the geometric anodic current density of 173 A m^-2. The electrochemical degradation of contaminants was achieved via the direct electron transfer, the anodically formed O₃, and by the OH^• radicals formed by the decomposition of H₂O₂ produced at the cathode. The identified transformation products of iopromide show that the anodic cleavage of all three C-I bonds at the aromatic ring was preferential over scissions at the alkyl side chains, suggesting a determining role of the π- π interactions with the graphene surface. In the presence of 20 mM sodium chloride (NaCl), the current efficiency for chlorine production was <0.04%, and there was no chlorate and perchlorate formation, demonstrating a very low electrocatalytic activity of the graphene-based sponge anode towards chloride. Graphene-based sponges were produced using a low-cost, bottom-up method that allows easy introduction of dopants and functionalization of the reduced graphene oxide coating, and thus tailoring of the material for the removal of specific contaminants.

Degradation of metoprolol from wastewater in a bio-electro-Fenton system

Advanced oxidation processes (AOPs) have been intensely studied for the removal of refractory pollutants because of the strong oxidizing capacity of hydroxyl radical. One of the emerging AOP methods gaining increased attention is bio-electro-Fenton (BEF) which can generate hydroxyl radical in-situ in the cathode chamber using the energy harvested by exoelectrogenic bacteria in the anode. In this study, the feasibility of BEF technology for the removal of metoprolol, a typical micropollutant widely found in the water environment, was for the first time investigated. It was found that applied voltage and working pH had a significant effect on removal efficiency while Fe²⁺ dosage as catalyst showed a little effect. Besides removal by hydroxyl radical, metoprolol might be adsorbed on the surface of the reactor, electrode, and precipitated with iron sludge, especially at neutral pH. In a batch experiment with a supplied voltage of 0.2 V, pH 3, and a Fe²⁺ dose of 0.2 mM, the removal rate of metoprolol in the BEF for the synthetic wastewater and the real effluent from the secondary sediment tank was 66% and 55% within 12 h, respectively. A possible degradation pathway was proposed. Then the removal of metoprolol in a continuous flow BEF system was further studied at different hydraulic retention times (HRTs) of 2, 4, and 6 h, about 77%, 92%, and 95% removal was observed. A toxicity test (less than 20% inhibition on bioluminescence) during treatment and energy cost analysis (5.269 × 10^-3 kWh/order/m³) in treating 10 μg/L of metoprolol containing wastewater effluent at continuous flow mode implied that the proposed BEF has a potential for wastewater treatment.

Metoprolol and Its Degradation and Transformation Products Using AOPs-Assessment of Aquatic Ecotoxicity Using QSAR

Pharmaceuticals are found in waterbodies worldwide. Conventional sewage treatment plants are often not able to eliminate these micropollutants. Hence, Advanced Oxidation Processes (AOPs) have been heavily investigated. Here, metoprolol is exposed to UV irradiation, hydrogen peroxide, and ozonation. Degradation was analyzed using chemical kinetics both for initial and secondary products. Photo-induced irradiation enhanced by hydrogen peroxide addition accelerated degradation more than ozonation, leading to complete elimination. Degradation and transformation products were identified by high-performance liquid-chromatography coupled to high-resolution higher-order mass spectrometry. The proposed structures allowed to apply Quantitative Structure-Activity Relationship (QSAR) analysis to predict ecotoxicity. Degradation products were generally associated with a lower ecotoxicological hazard to the aquatic environment according to OECD QSAR toolbox and VEGA. Comparison of potential structural isomers suggested forecasts may become more reliable with larger databases in the future.

Electrochemical treatments of coking wastewater and coal gasification wastewater with Ti/Ti4O7 and Ti/RuO2-IrO2 anodes

Electrochemical treatments of coking wastewater (CW) and coal gasification wastewater (CGW) were conducted with Ti/Ti₄O₇ and Ti/RuO₂-IrO₂ anodes. The performances of Ti/Ti₄O₇ and Ti/RuO₂-IrO₂ anodes were investigated by analyzing the effects of five key influencing factors including anodes material, current density, anode-cathode distance, initial pH value, and electrolyte type. The removal efficiencies of total organic carbon (TOC) were analyzed during the processes of CW and CGW electro-oxidation. The removal efficiencies of sixteen polynuclear aromatic hydrocarbons (PAHs) in CW and CGW by electro-oxidation were also explored to further assess the electrochemical activities of Ti/Ti₄O₇ and Ti/RuO₂-IrO₂ anodes. The Ti/Ti₄O₇ anode achieved 78.7% COD removal efficiency of CW, 85.8% COD removal efficiency of CGW, 50.3% TOC removal efficiency of CW, and 54.8% TOC removal efficiency of CGW, higher than the Ti/RuO₂-IrO₂ anode (76.7%, 78.1%, 44.8% and 46.8%). The COD removal efficiencies increased with the applied current density, decreased with the increase of the anode-cathode distance, and slightly decreased with the increase of the initial pH value. Meanwhile, the removal efficiencies of sixteen PAHs by the Ti/Ti₄O₇ anode were mostly higher than those by the Ti/RuO₂-IrO₂ anode. By comprehensively analyzing the performances of Ti/Ti₄O₇ and Ti/RuO₂-IrO₂ anodes on electrochemical treatments of CW and CGW, this study may supply insights into the application potentials of these anodes to the electrochemical treatments of real wastewater.

Comparative evaluation of metoprolol degradation by UV/chlorine and UV/H2O2 processes

The degradation of metoprolol (MTP), a β-blocker commonly used for cardiovascular diseases, by UV/chlorine and UV/H₂O₂ processes was comparatively evaluated. MTP direct photolysis at 254 nm could be neglected, but remarkable MTP degradation was observed in both the UV/chlorine and UV/H₂O₂ systems. Compared with UV/H₂O₂, UV/chlorine has a more pronounced MTP degradation efficiency. In addition to primary radicals (OH and Cl), secondary radicals (ClO and Cl₂^-) played a pivotal role in degrading MTP by UV/chlorine process. The relative contributions of hydroxyl radicals (OH) and reactive chlorine species (RCS) in the UV/chlorine system varied at different solution pH values (i.e., the contribution of RCS increased from 57.7% to 75.1% as the pH increased from 6 to 8). The degradation rate rose as the oxidant dosage increased in the UV/chlorine and UV/H₂O₂ processes. The presence of Cl^- slightly affected MTP degradation in both processes, while the existence of HCO₃^- and HA inhibited MTP degradation to different extents in both processes. In terms of the overall cost of electrical energy, UV/chlorine is more cost efficient than UV/H₂O₂. The degradation products during the two processes were identified and compared, and the degradation pathways were proposed accordingly. Compared with the direct chlorination of MTP, pre-oxidation with UV/chlorine and UV/H₂O₂ significantly enhanced the formation of commonly known DBPs. Therefore, when using UV/chlorine and UV/H₂O₂ in real waters to remove organic pollutants, the possible risk of enhanced DBP formation resulting from the degradation of certain pollutants during post-chlorination should be carefully considered.

Absolute removal of ciprofloxacin and its degraded byproducts in aqueous solution using an efficient electrochemical oxidation process coupled with adsorption treatment technique

Pharmaceutical-based contaminants are the major reasons for morbidity and mortality in aquatic animals and lead to several side effects and diseases in human community. Availability of proper, efficient, and cost-effective treatment technologies is still scarce. In this study, an efficient combined treatment technique (electrochemical oxidation and adsorption processes) was developed for the complete detoxification of most commonly used antibiotic, ciprofloxacin in aqueous solution. Electrochemical degradation of ciprofloxacin was performed using titanium-based tri-metal oxide mesh type anode, and the effective oxidative potential, electrolysis time, and pH for the degradation of ciprofloxacin were thoroughly evaluated. Sulfate, fluoride ions and toxic byproducts generated during electrochemical oxidation of ciprofloxacin were subsequently removed through a simple adsorption treatment using activated charcoal for 90 min. Further, the toxicity of the treated water was assessed with the nematode Caenorhabditis elegans species at different time intervals by observing the expressions of important stress-responsive genes viz., sod-3, hsp-16.2, ctl-1,2,3 and gst-4. The results exhibited that the combined process of electrochemical oxidation and adsorption treatment is simple, low-cost as well as effective to eliminate ciprofloxacin and its toxic byproducts in aqueous solution.

The beneficial effect of cathodic hydrogen peroxide generation on mitigating chlorinated by-product formation during water treatment by an electro-peroxone process

The formation of chlorinated by-products is a major concern associated with electrochemical water treatment processes. This study investigated the formation of chlorinated by-products during surface water treatment by a newly developed electrochemical advanced oxidation process (EAOP), the electro-peroxone (E-peroxone) process, which couples ozonation with in situ electro-generation of hydrogen peroxide (H₂O₂) from cathodic oxygen reduction. Due to the enhanced ozone (O₃) conversion to hydroxyl radicals (•OH) by electro-generated H₂O₂, the E-peroxone process considerably accelerated the abatement of ozone-refractory micropollutants such as clofibric acid and chloramphenicol in the selected surface water compared to conventional ozonation. In addition, the cathodically generated H₂O₂ effectively quenched hypochlorous acid (HOCl) derived from the anodic oxidation of chloride in the surface water. Therefore, the formation of trichloromethane (TCM) and chloroacetic acids (CAAs) from the reactions of HOCl with dissolved organic matter (DOM) was insignificant during the E-peroxone process, and similar levels of TCM and CAAs were generally observed in the conventional ozonation and E-peroxone treated water. In contrast, considerable amounts of HOCl could be generated from the anodic oxidation of chloride and then accumulated in the surface water during conventional electrolysis process, which resulted in significantly higher concentrations of TCM and CAAs in the electrolysis treated water. The results of this study suggest that the E-peroxone process can overcome the major limitation of conventional electrochemical processes and provide an effective and safe EAOP alternative for micropollutant abatement during water treatment.

Chlorinated-Methylsiloxanes in Shengli Oilfield: Their Generation in Oil-Production Wastewater Treatment Plant and Presence in the Surrounding Soils

In two oil-wastewater treatment stations of Shengli Oilfield, cyclic volatile methylsiloxanes (cVMS, D4-D6) in the wastewater stream were found to undergo chlorination during electro-oxidation process for wastewater containing chlorine ions (16.1-42.0 g/L). Their converted fractions were 4.71-28.0% for monochlorinated D4-D6 and 0.22-7.96% for dichlorinated D4, which were ∼2 orders of magnitude higher than those for hydroxylated products. Furthermore, portions of chlorinated methylsiloxanes retained in excess sludge were released to the surrounding soils. In soil samples ( n = 500), chlorinated methylsiloxanes concentrations (<LOD-586 ng/g dw (dry weight), detection frequency (df) = 6.60-45.6%) decreased roughly exponentially with respect to the distance away from these two stations. During 2008-2017, the measured total chlorinated cVMS kept increasing in the dewatered-sludge (from 58.5 to 120 μg/g dw), while their concentrations in the surrounding soils doubled (from 93.4 to 184 ng/g dw) in first 6 years, but decreased since then (48.0 ng/g at 2017). Simulating experiments showed that monochlorinated D4-D6 in soil had 1.1-2.4 times longer hydrolysis (6.92-234 days) and volatilization (4.62-325 days) half-lives than their paired nonchlorinated cVMS. Among isomers of dichlorinated D4, D3D(CHCl₂) had greatest hydrolysis (7.75-33.8 days) and volatilization (135-271 days) rates, followed by D3D(CH₂Cl)₂, D2(D(CH₂Cl))₂ and DD(CH₂Cl)DD(CH₂Cl).

Carbon fiber-assisted iron carbide nanoparticles as an efficient catalyst via peroxymonosulfate activation for organic contaminant removal

The introduction of carbon fibers enhances the ability of iron carbide nanoparticles to activate PMS to remove contaminants.

Cytostatic drug removal using electrochemical oxidation with BDD electrode: Degradation pathway and toxicity

In the presented study, electrochemical oxidation of five anticancer drugs (5-fluorouracil (5-FU), ifosfamide (IF), cyclophosphamide (CF), methotrexate (MTX), imatinib (IMB)) using boron doped diamond (BDD) electrode was investigated. In the first step the operating parameters of electrolysis were optimized. Studies have demonstrated a significant influence of applying current density, temperature, pH of solution and initial concentration of 5-FU on the process efficiency. A comparison of the decomposition rate of all the tested drugs showed a decrease in the pseudo-first order rate constants in the following order: k(IMB) > k(MTX) > k(CF) ≈ k(IF) > k(5-FU). Mineralization current efficiency (MCE) was determined for all the drugs based on the removal amount of total organic carbon (TOC) and their values decreased in the same order as values of drug degradation rate k. Based on the identified degradation products, electrochemical oxidation pathways of the decomposed drugs were proposed. In the case of CF, IF and 5-FU the degradation process occurred mainly through ketonization, hydroxylation and dehalogenation, while MTX and IMB were decomposed by attack of hydroxyl radicals on benzyl position in parent compounds. An important part of the research was the evaluation of eco-toxicity of electrochemically treated drug solutions against Lemna minor. Toxicity of initial 5-FU and MTX solutions towards L. minor were observed but after electrochemical treatment its toxicity decreased. The opposite trend was observed for CF and IF. In this case no significant toxicity was observed for the initial solutions of these drugs, while after electrochemical treatment an increase in growth inhibition of L. minor was found.

Electrochemical Transformations of Perfluoroalkyl Acid (PFAA) Precursors and PFAAs in Groundwater Impacted with Aqueous Film Forming Foams

While oxidative technologies have been proposed for treatment of waters impacted by aqueous film forming foams (AFFFs), information is lacking regarding the transformation pathways for the chemical precursors to the perfluoroalkyl acids (PFAAs) typically present in such waters. This study examined the oxidative electrochemical treatment of poly- and perfluoroalkyl substances (PFASs) for two AFFF-impacted groundwaters. The bulk pseudo first order rate constant for PFOA removal was 0.23 L h^-1 A^-1; for PFOS, this value ranged from 0.084 to 0.23 L h^-1 A^-1. Results from the first groundwater studied suggested a transformation pathway where sulfonamide-based PFASs transformed to primarily perfluorinated sulfonamides and perfluorinated carboxylic acids (PFCAs), with subsequent defluorination of the PFCAs. Transient increases in the perfluorinated sulfonamides and PFCAs were observed. For the second groundwater studied, no transient increases in PFAAs were measured, despite the presence of similarly structured suspected PFAA precursors and substantial defluorination. For both waters, suspected precursors were the primary sources of the generated fluoride. Assessment of precursor compound transformation noted the formation of keto-perfluoroalkanesulfonates only in the second groundwater. These results confirm that oxidation and defluorination of suspected PFAA precursors in the second groundwater underwent transformation via a pathway different than that of the first groundwater, which was not captured by total oxidizable precursor assay.

Investigation and improvement of a novel double-working-electrode electrochemical system for organic matter treatment from high-salinity wastewater

The novel double-working-electrode electrochemical system with air diffusion cathode (ADC) and Ti/SnO₂-Sb anode (TSSA) has shown higher efficiency and lower energy consumption for the degradation of organic pollutant from high-salinity wastewater, compared to the traditional single anode system. To further investigate and improve this system, in this work, firstly the effect of vital factors of the double-working-electrode electrochemical system including initial methyl orange (MO) concentration, NaCl concentration and initial pH value of organic solution were investigated, using MO as the targeted organic pollutant, carbon black ADC (CBAC) as cathode and stainless steel mesh electrode (SSME) as control. Besides, for the further improvement of removal performance, a novel home-made activated carbon-ADC (ACAC) was studied as cathode with the same investigation process. The results showed that, in the experiments studying the effect of both initial MO and NaCl concentrations, the removal performance was in the order of TSSA-ACAC > TSSA-CBAC > TSSA-SSME in all conditions of initial MO and NaCl concentrations. However, with the pH value reduced from 6.0 to 3.0, the performances of three systems turned to be much closer to each other. Besides, ACAC played a synergistic role in MO removal by greatly improving the MO removal performance and enhancing its adaptability to the reactor parametric variation. ACAC created a weak acidic environment for accelerating the indirect electro-oxidation of MO on TSSA. The MO degradation pathways in the three systems were the same but the TSSA-ACAC system gave a higher degradation kinetics order.

Identification and characterization of photodegradation products of metoprolol in the presence of natural fulvic acid by HPLC-UV-MSn

Metoprolol is a β-blocker highly prescribed for the treatment of heart diseases. It is not efficiently removed in wastewater treatment plants and it has been detected not only in the treated effluents, but also in natural waters. Thus, the knowledge of its fate in the environment is an important issue, and photodegradation is an important degradation pathway. While direct photodegradation of metoprolol by solar light is not relevant, there is evidence in the literature that it suffers indirect photodegradation and a few studies have been published showing the important role of dissolved humic matter as photo-sensitizer. However, the identification of the photoproducts formed in the presence of humic matter is very poor, since only 2 photoproducts had been identified. This study investigated the degradation of metoprolol under simulated solar radiation and in the presence of fulvic acids (FA) extracted from a river. During the photodegradation experiments we observed the formation of new compounds which were separated and tentatively identified by HPLC-UV-ESI-MSⁿ. At least 16 compounds were tentatively identified, including the 2 compounds previously identified in the literature and 4 new compounds which had not been detected by other authors as degradation products of metoprolol, even when submitted to artificial degradation processes.

Electrochemical degradation of the antihypertensive losartan in aqueous medium by electro-oxidation with boron-doped diamond electrode

In this work the electrochemical oxidation of losartan, an emerging pharmaceutical pollutant, was studied. Electrochemical oxidation was carried out in batch mode, in an open and undivided cell of 100cm(3) using a boron-doped diamond (BDD)/stainless steel system. With Cl(-) medium 56% of mineralization was registered, while with the trials containing SO4(2-) as supporting electrolyte a higher mineralization yield of 67% was reached, even obtaining a total removal of losartan potassium at 80mAcm(-2) and 180min of reaction time at pH 7.0. Higher losartan potassium concentrations enhanced the mineralization degree and the efficiency of the electrochemical oxidation process. During the mineralization up to 4 aromatic intermediates were identified by ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Moreover, short-linear carboxylic acids, like oxalic, succinic and oxamic were detected and quantified by ion-exclusion HPLC. Finally, the ability of the electrochemical oxidation process to mineralize dissolved commercial tablets containing losartan was achieved, obtaining TOC removal up to 71% under optimized conditions (10mAcm(-2), 0.05M Na2SO4, pH 7.0 and 25°C and 360min of electrolysis).

Bioelectro-Fenton: A sustainable integrated process for removal of organic pollutants from water: Application to mineralization of metoprolol

The relevant environmental hazard related to the presence of pharmaceuticals in water sources requires the development of high effective and suitable wastewater treatment technologies. In the present work, a hybrid process coupling electro-Fenton (EF) process and aerobic biological treatment (Bio-EF process) was implemented for the efficient and cost-effective mineralization of beta-blocker metoprolol (MPTL) aqueous solutions. Firstly, operating factors influencing EF process were assessed. MTPL solutions were completely mineralized after 4h-electrolysis under optimal operating conditions and BDD anode demonstrated its oxidation superiority. The absolute rate constant of MTPL oxidation byOH (kMTPL) was determined by the competition kinetics method and found to be (1.72±0.04)×10(9)M(-1)s(-1). A reaction pathway for the mineralization of the drug was proposed based on the identification of oxidation by-products. Secondly, EF process was used as pre-treatment. An increase of BOD5/COD ratio from 0.012 to 0.44 was obtained after 1h EF treatment, along with 47% TOC removal and a significant decrease of toxicity, demonstrating the feasibility of a post-biological treatment. Finally, biological treatment successfully oxidized 43% of the total TOC content. An overall 90% mineralization of MPTL solutions was achieved by the Bio-EF process, demonstrating its potentiality for treating wastewater containing pharmaceutical residues.

Identification of transformation products during advanced oxidation of diatrizoate: Effect of water matrix and oxidation process

Removal of micropollutants from reverse osmosis (RO) brines of wastewater desalination by oxidation processes is influenced by the scavenging capacity of brines components, resulting in the accumulation of transformation products (TPs) rather than complete mineralization. In this work the iodinated contrast media diatrizoate (DTZ) was used as model compound due to its relative resistance to oxidation. Identification of TPs was performed in ultrapure water (UPW) and RO brines applying nonthermal plasma (NTP) and UVA-TiO2 as oxidation techniques. The influence of main RO brines components in the formation and accumulation of TPs, such as chloride, bicarbonate alkalinity and humic acid, was also studied during UVA-TiO2. DTZ oxidation pattern in UPW resulted similar in both UVA-TiO2 and NTP achieving 66 and 61% transformation, respectively. However, DTZ transformation in RO brines was markedly lower in UVA-TiO2 (9%) than in NTP (27%). These differences can be attributed to the synergic effect of RO brines components during NTP. Moreover, reactive species other than hydroxyl radical contributed to DTZ transformation, i.e., direct photolysis in UVA-TiO2 and direct photolysis + O3 in NTP accounted for 16 and 23%, respectively. DTZ transformation led to iodide formation in both oxidation techniques but it further oxidized to iodate by ozone in NTP. In total 14 transformation products were identified in UPW of which 3 were present only in UVA-TiO2 and 2 were present exclusively in NTP; 5 of the 14 TPs were absent in RO brines. Five of them were new and were denoted as TP-474A/B, TP-522, TP-586, TP-602, TP-628. TP-522 (mono-chlorinated) was elucidated only in presence of high chloride titer-synthetic water matrix in NTP, most probably formed by active chlorine species generated in situ. TPs accumulation in RO brines was markedly different in comparison to UPW. This denotes the influence of RO brines components in the formation of reactive species that could further attack DTZ/TPs and/or scavenging performed by these brine components that could limit further TPs degradation. Five plausible degradation pathways are proposed for DTZ transformation in UPW.

Electrochemical Transformation of Trace Organic Contaminants in Latrine Wastewater

Solar-powered electrochemical systems have shown promise for onsite wastewater treatment in regions where basic infrastructure for conventional wastewater treatment is not available. To assess the applicability of these systems for trace organic contaminant treatment, test compound electrolysis rate constants were measured in authentic latrine wastewater using mixed-metal oxide anodes coupled with stainless steel cathodes. Complete removal of ranitidine and cimetidine was achieved within 30 min of electrolysis at an applied potential of 3.5 V (0.7 A L(-1)). Removal of acetaminophen, ciprofloxacin, trimethoprim, propranolol, and carbamazepine (>80%) was achieved within 3 h of electrolysis. Oxidation of ranitidine, cimetidine, and ciprofloxacin was primarily attributed to reaction with NH2Cl. Transformation of trimethoprim, propranolol, and carbamazepine was attributed to direct electron transfer and to reactions with surface-bound reactive chlorine species. Relative contributions of aqueous phase ·OH, ·Cl, ·Cl2(-), HOCl/OCl(-), and Cl2 were determined to be negligible based on measured second-order reaction rate constants, probe compound reaction rates, and experiments in buffered Cl(-) solutions. Electrical energy per order of removal (EEO) increased with increasing applied potentials and current densities. Test compound removal was most efficient at elevated Cl(-) concentrations present when treated wastewater is recycled for use as flushing water (i.e., ∼ 75 mM Cl(-); EEO = 0.2-6.9 kWh log(-1) m(-3)). Identified halogenated and oxygenated electrolysis products typically underwent further transformations to unidentifiable products within the 3 h treatment cycle. Identifiable halogenated byproduct formation and accumulation was minimized during electrolysis of wastewater containing 75 mM Cl(-).

Removal of Persistent Organic Contaminants by Electrochemically Activated Sulfate

Solutions of sulfate have often been used as background electrolytes in the electrochemical degradation of contaminants and have been generally considered inert even when high-oxidation-power anodes such as boron-doped diamond (BDD) were employed. This study examines the role of sulfate by comparing electro-oxidation rates for seven persistent organic contaminants at BDD anodes in sulfate and inert nitrate anolytes. Sulfate yielded electro-oxidation rates 10-15 times higher for all target contaminants compared to the rates of nitrate anolyte. This electrochemical activation of sulfate was also observed at concentrations as low as 1.6 mM, which is relevant for many wastewaters. Electrolysis of diatrizoate in the presence of specific radical quenchers (tert-butanol and methanol) had a similar effect on electro-oxidation rates, illustrating a possible role of the hydroxyl radical ((•)OH) in the anodic formation of sulfate radical (SO4(•-)) species. The addition of 0.55 mM persulfate increased the electro-oxidation rate of diatrizoate in nitrate from 0.94 to 9.97 h(-1), suggesting a nonradical activation of persulfate. Overall findings indicate the formation of strong sulfate-derived oxidant species at BDD anodes when polarized at high potentials. This may have positive implications in the electro-oxidation of wastewaters containing sulfate. For example, the energy required for the 10-fold removal of diatrizoate was decreased from 45.6 to 2.44 kWh m(-3) by switching from nitrate to sulfate anolyte.

Challenges and Opportunities for Electrochemical Processes as Next-Generation Technologies for the Treatment of Contaminated Water

Electrochemical processes have been extensively investigated for the removal of a range of organic and inorganic contaminants. The great majority of these studies were conducted using nitrate-, perchlorate-, sulfate-, and chloride-based electrolyte solutions. In actual treatment applications, organic and inorganic constituents may have substantial effects on the performance of electrochemical treatment. In particular, the outcome of electrochemical oxidation will depend on the concentration of chloride and bromide. Formation of chlorate, perchlorate, chlorinated, and brominated organics may compromise the quality of the treated effluent. A critical review of recent research identifies future opportunities and research needed to overcome major challenges that currently limit the application of electrochemical water treatment systems for industrial and municipal water and wastewater treatment. Given the increasing interest in decentralized wastewater treatment, applications of electrolytic systems for treatment of domestic wastewater, greywater, and source-separated urine are also included. To support future adoption of electrochemical treatment, new approaches are needed to minimize the formation of toxic byproducts and the loss of efficiency caused by mass transfer limitations and undesired side reactions. Prior to realizing these improvements, recognition of the situations where these limitations pose potential health risks is a necessary step in the design and operation of electrochemical treatment systems.

Electrochemical oxidation of tramadol in low-salinity reverse osmosis concentrates using boron-doped diamond anodes

The electrochemical treatment of low-salinity reverse osmosis (RO) concentrates was investigated using tramadol (100 μM) as a model substance for persistent organic contaminants. Galvanostatic degradation experiments using boron-doped diamond electrodes at different applied currents were conducted in RO concentrates as well as in ultra-pure water containing either sodium chloride or sodium sulfate. Kinetic investigations revealed a significant influence of in-situ generated active chlorine besides direct anodic oxidation. Therefore, tramadol concentrations decreased more rapidly at elevated chloride content. Nevertheless, reduction of total organic carbon (TOC) was found to be comparatively low, demonstrating that transformation rather than mineralization was taking place. Early stage product formation could be attributed to both direct and indirect processes, including demethylation, hydroxylation, dehydration, oxidative aromatic ring cleavage and halogenation reactions. The latter led to various halogenated derivatives and resulted in AOX (adsorbable organic halogens) formation in the lower mg/L-range depending on the treatment conditions. Characterisation of transformation products (TPs) was achieved via MS(n) experiments and additional NMR measurements. Based on identification and quantification of the main TPs in different matrices and on additional potentiostatic electrolysis, a transformation pathway was proposed.

Heterogeneous electro-Fenton using modified iron-carbon as catalyst for 2,4-dichlorophenol degradation: influence factors, mechanism and degradation pathway

Modified iron-carbon with polytetrafluoroethylene (PTFE) was firstly investigated as heterogeneous electro-Fenton (EF) catalyst for 2,4-dichlorophenol (2,4-DCP) degradation in near neutral pH condition. The catalyst was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), and the effects of some important operating parameters such as current intensity and pH on the 2,4-DCP degradation were investigated. After the catalyst modification with 20% PTFE, the degradation performance maintained well with much lower iron leaching, and at current intensity 100 mA, initial pH 6.7, catalyst loading 6 g/L, the degradation efficiency of 2,4-DCP could exceed 95% within 120 min treatment. Two-stage pseudo first-order kinetics of 2,4-DCP degradation was observed, including a slow anodic oxidation stage (first-stage) and much faster heterogeneous EF oxidation (second-stage), in which the automatic drop of pH in the first-stage initiated the Fe(2+) release from micro-electrolysis and thus benefited to the subsequent EF reaction. Aromatic intermediates such as 3,5-dichlorocatechol, 4,6-dichlororesorcinol and 2-chlorohydroquinone were detected by GC-MS. Oxalic acid, acetic acid, formic acid and Cl(-) were quantified by ion chromatograph. Based on these analysis as well as the detection of H₂O₂ and OH, a possible mechanism and degradation pathway for 2,4-DCP were proposed. This work demonstrated that such a heterogeneous EF using cheap modified Fe-C catalyst was promising for organic wastewater treatment in initial neutral pH condition.

Preparation and Electrocatalytic Performance of Bi-Modified Quartz Column Particle Electrode for Phenol Degradation

Bismuth oxide (Bi2O3) and its composites have good electrocatalytic performance. Quartz column is a good kind of catalyst carrier with the characteristics of high mechanical strength and good stability. A novel Bi-modified quartz column particle electrode (BQP) was prepared by the dipping-calcination method. The characterization results revealed that Bi2O3was successfully loaded on quartz column. The optimum preparation condition was calcining at 550°C for 4 h. Electrocatalytic performance was evaluated by the degradation of phenol and the results indicated that the triclinic phase of Bi2O3showed the best electrocatalytic property. Besides, when the dosage concentration of the particle electrode was 125 g/L and the electrolytic voltage was 12 V, the degradation rate of phenol (200 mg/L) reached the highest (94.25%), compared with 70.00% of that in two-dimensional (2D) system. In addition, the removal rate of chemical oxygen demand (COD) was 75.50%, compared with 53.30% of that in 2D system. The reusability and regeneration of BQP were investigated and the results were good. Mechanism of enhanced electrochemical oxidation by BQP was evaluated by the capture of hydroxyl radical.

Metal oxide-coated anodes in wastewater treatment

Electrochemical oxidation is an effective wastewater treatment method. Metal oxide-coated substrates are commonly used as anodes in this process. This article compiles the developments in the fabrication, application, and performance of metal oxide anodes in wastewater treatment. It summarizes the preparative methods and mechanism of oxidation of organics on the metal oxide anodes. The discussion is focused on the application of SnO2, PbO2, IrO2, and RuO2 metal oxide anodes and their effectiveness in wastewater treatment process.

Degradation of β-blockers in hospital wastewater by means of ozonation and Fe2+/ozonation

This study investigates the degradation of the β-blockers in hospital wastewater by direct ozonation and Fe2+/ozonation with a focus on measurements at different initial pHs and Fe2+ concentrations, and the determination of kinetic constants. The results showed that these 'emerging contaminants' were completely degraded, when the removal rate of organic matter reached 30.6% and 49.1% for ozonation and Fe2+/ozonation, respectively. Likewise, the aromaticity removal rates were 63.4% and 77.9% for ozonation and Fe2+/ozonation, respectively. The experimental design showed that pH was the variable which had the greatest effect on the Fe2+/ozonation. The kinetic constants of atenolol, metoprolol and propranolol degradation by direct ozonation complied with pseudo-first-order conditions, while Fe2+/ozonation was suited to a biphasic degradation model. The k obs tended to rise when the pH increases; propranolol showed high k obs, which can be attributed to the naphthalene group (an electron-rich moiety). The identification of degradation products was carried out in aqueous solution using HPLC-MS2, followed by a suggestion of degradation pathways by means of ozonation. The degradation products proved to be dependent on the initial pH, and followed pathways that are based on direct ozonolysis and free radicals.

Removal of the X-ray contrast media diatrizoate by electrochemical reduction and oxidation

Due to their resistance to biological wastewater treatment, iodinated X-ray contrast media (ICM) have been detected in municipal wastewater effluents at relatively high concentrations (i.e., up to 100 μg L(-1)), with hospitals serving as their main source. To provide a new approach for reducing the concentrations of ICMs in wastewater, electrochemical reduction at three-dimensional graphite felt and graphite felt doped with palladium nanoparticles was examined as a means for deiodination of the common ICM diatrizoate. The presence of palladium nanoparticles significantly enhanced the removal of diatrizoate and enabled its complete deiodination to 3,5-diacetamidobenzoic acid. When the system was employed in the treatment of hospital wastewater, diatrizoate was reduced, but the extent of electrochemical reduction decreased as a result of competing reactions with solutes in the matrix. Following electrochemical reduction of diatrizoate to 3,5-diacetamidobenzoic acid, electrochemical oxidation with boron-doped diamond (BDD) anodes was employed. 3,5-Diacetamidobenzoic acid disappeared from solution at a rate that was similar to that of diatrizoate, but it was more readily mineralized than the parent compound. When electrochemical reduction and oxidation were coupled in a three-compartment reactor operated in a continuous mode, complete deiodination of diatrizoate was achieved at an applied cathode potential of -1.7 V vs SHE, with the released iodide ions electrodialyzed in a central compartment with 80% efficiency. The resulting BDD anode potential (i.e., +3.4-3.5 V vs SHE) enabled efficient oxidation of the products of the reductive step. The presence of other anions (e.g., chloride) was likely responsible for a decrease in I(-) separation efficiency when hospital wastewater was treated. Reductive deiodination combined with oxidative degradation provides benefits over oxidative treatment methods because it does not produce stable iodinated intermediates. Nevertheless, the process must be further optimized for the conditions encountered in hospital wastewater to improve the separation efficiency of halide ions prior to the electrooxidation step.

Electrochemical mineralization of pentachlorophenol (PCP) by Ti/SnO2-Sb electrodes

Electrochemical degradation of pentachlorophenol (PCP) in aqueous solution was investigated over Ti/SnO2-Sb electrodes prepared by sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements were used to characterize the physicochemical properties of the electrodes. The electrochemical degradation of PCP followed pseudo-first-order kinetics. The main influencing factors, including the types of supporting electrolyte (i.e., NaClO4, Na2SO4, Na2SO3, NaNO3, and NaNO2), initial concentrations of PCP (5-1000mgL(-1)), pH values (3.0-11.0), and current densities (5-40mAcm(-2)) were evaluated. The degradation and mineralization ratios of 100mgL(-1) of PCP achieved >99.8% and 83.0% after 30min electrolysis with a 10mmolL(-1) Na2SO4 at a current density of 10mAcm(-2), respectively. The corresponding half-life time (t1/2) was 3.94min. The degradation pathways that were involved in dechlorination, protons generation, and mineralization processes were proposed based on the determination of total organic carbon, chloride, and intermediate products (i.e., low chlorinated phenol and some organic acids). The toxicity of PCP and its intermediates could be reduced effectively by electrolysis. These results showed that electrochemical technique could achieve a significant mineralization rate in a short time (<30min), which provided an efficient way for PCP elimination from wastewater.

Oxidation-coagulation of β-blockers by K2FeVIO4 in hospital wastewater: assessment of degradation products and biodegradability

This study investigated the degradation of atenolol, metoprolol and propranolol beta-blockers by ferrate (K2FeO4) in hospital wastewater and in aqueous solution. In the case of hospital wastewater, the effect of the independent variables pH and [Fe(VI)] was evaluated by means of response surface methodology. The results showed that Fe(VI) plays an important role in the oxidation-coagulation process, and the treatment of the hospital wastewater led to degradations above 90% for all the three β-blockers, and to reductions of aromaticity that were close to 60%. In addition, only 17% of the organic load was removed. In aqueous solution, the degradation of the β-blockers atenolol, metoprolol and propranolol was 71.7%, 24.7% and 96.5%, respectively, when a ratio of 1:10 [β-blocker]:[Fe(VI)] was used. No mineralization was achieved, which suggests that there was a conversion of the β-blockers to degradation products identified by liquid chromatography/mass spectrometry tandem. Degradation pathways were proposed, which took account of the role of Fe(VI). Furthermore, the ready biodegradability of the post-process samples was evaluated by using the closed bottle test, and showed an increase in biodegradability. The use of the ferrate advanced oxidation technology seems to be a useful means of ensuring the remediation of hospital and similar wastewater.

Electrochemical oxidation of electrodialysed reverse osmosis concentrate on Ti/Pt-IrO2, Ti/SnO2-Sb and boron-doped diamond electrodes

Reverse osmosis concentrate from wastewater reclamation contains biorefractory trace organic contaminants that may pose environmental or health hazard. Due to its high conductivity, electrochemical oxidation of brine requires low voltage which is energetically favourable. However, the presence of chloride ions may lead to the formation of chlorinated by-products, which are likely to exert an increased toxicity and persistence to further oxidation than their non-chlorinated analogues. Here, the performance of Ti/Pt-IrO(2), Ti/SnO(2)-Sb and Si/BDD anodes was evaluated for the electrochemical oxidation of ROC in the presence of chloride, nitrate or sulfate ions (0.05 M sodium salts). In order to investigate the electrooxidation of ROC with nitrate and sulfate ions as dominant ion mediators, chloride ion concentration was decreased 10 times by electrodialytic pretreatment. The highest Coulombic efficiency for chemical oxygen demand (COD) removal was observed in the presence of high chloride ions concentration for all anodes tested (8.3-15.9%). Electrooxidation of the electrodialysed concentrate at Ti/SnO(2)-Sb and Ti/Pt-IrO(2) electrodes exhibited low dissolved organic carbon (DOC) (i.e. 23 and 12%, respectively) and COD removal (i.e. 37-43 and 6-22%, respectively), indicating that for these electrodes chlorine-mediated oxidation was the main oxidation mechanism, particularly in the latter case. In contrast, DOC removal for the electrodialysed concentrate stream was enhanced at Si/BDD anode in the presence of SO(4)(2-) (i.e. 51%) compared to NO(3)(2-) electrolyte (i.e. 41%), likely due to the contribution of SO(4)(·-) and S(2)O(8)(2-) species to the oxidative degradation. Furthermore, decreased concentration of chloride ions lead to a lower formation of haloacetic acids and trihalomethanes at all three electrodes tested.

Assessment of degradation byproducts and NDMA formation potential during UV and UV/H2O2 treatment of doxylamine in the presence of monochloramine

UV-C radiation is the U.S. EPA recommended technology to remove N-nitrosodimethylamine (NDMA) during drinking and recycled water production. Frequently, H(2)O(2) is added to the treatment to remove other recalcitrant compounds and to prevent NDMA reformation. However, the transformation of NDMA precursors during the UV and UV/H(2)O(2) process and the consequences for NDMA formation potential are currently not well understood, in particular in the presence of monochloramine. In this study, doxylamine has been chosen as a model compound to elucidate its degradation byproducts in the UV and UV/H(2)O(2) process and correlate those with changes to the NDMA formation potential. This study shows that during UV treatment in the presence and absence of monochloramine, NDMA formation potential can be halved. However, an increase of more than 30% was observed when hydrogen peroxide was added. Ultrafast liquid chromatography coupled to quadrupole-linear ion trap mass spectrometer was used for screening and structural elucidation of degradation byproducts identifying 21 chemical structures from the original parent compound. This work shows that further oxidation of NDMA precursors does not necessarily lead to a decrease in NDMA formation potential. Degradation byproducts with increased electron density in the vicinity of the dimethylamino moiety, for example induced by hydroxylation, may have a higher yield of nucleophilic substitution and subsequent NDMA formation compared to the parent compound during chloramination. This work demonstrates the need to consider the formation of oxidation byproducts and associated implications for the control and management of NDMA formation in downstream processes and distribution when integrating oxidative treatments into a treatment train generating either drinking water or recycled water for potable reuse.

Recent advances in environmental risk assessment of transformation products

When micropollutants degrade in the environment, they may form persistent and toxic transformation products, which should be accounted for in the environmental risk assessment of the parent compounds. Transformation products have become a topic of interest not only with regard to their formation in the environment, but also during advanced water treatment processes, where disinfection byproducts can form from benign precursors. In addition, environmental risk assessment of human and veterinary pharmaceuticals requires inclusion of human metabolites as most pharmaceuticals are not excreted into wastewater in their original form, but are extensively metabolized. All three areas have developed their independent approaches to assess the risk associated with transformation product formation including hazard identification, exposure assessment, hazard assessment including dose-response characterization, and risk characterization. This review provides an overview and defines a link among those areas, emphasizing commonalities and encouraging a common approach. We distinguish among approaches to assess transformation products of individual pollutants that are undergoing a particular transformation process, e.g., biotransformation or (photo)oxidation, and approaches with the goal of prioritizing transformation products in terms of their contribution to environmental risk. We classify existing approaches for transformation product assessment in degradation studies as exposure- or effect-driven. In the exposure-driven approach, transformation products are identified and quantified by chemical analysis followed by effect assessment. In the effect-driven approach, a reaction mixture undergoes toxicity testing. If the decrease in toxicity parallels the decrease of parent compound concentration, the transformation products are considered to be irrelevant, and only when toxicity increases or the decrease is not proportional to the parent compound concentration are the TPs identified. For prioritization of transformation products in terms of their contribution to overall environmental risk, we integrate existing research into a coherent model-based, risk-driven framework. In the proposed framework, read-across from data of the parent compound to the transformation products is emphasized, but limitations to this approach are also discussed. Most prominently, we demonstrate how effect data for parent compounds can be used in combination with analysis of toxicophore structures and bioconcentration potential to facilitate transformation product effect assessment.