Effective mineralization of anti-epilepsy drug carbamazepine in aqueous solution by simultaneously electro-generated H2O2/O3 process

Insight into the generation of toxic by-products during UV/H2O2 degradation of carbamazepine: Mechanisms, N-transformation and toxicity

Carbamazepine (CBZ) is a widely used anticonvulsant drug that has been detected in aquatic environments. This study investigated the toxicity of its by-products (CBZ-BPs), which may surpass CBZ. Unlike the previous studies, this study offered a more systematic approach to identifying toxic BPs and inferring degradation pathways. Furthermore, quadrupole time-of-flight (QTOF) and density functional theory (DFT) calculations were employed to analyze CBZ-BP structures and degradation pathways. Evaluation of total organic carbon (TOC) and total nitrogen (TN) mineralization rates, revealed carbon (C) greater susceptibility to mineralization compared with nitrogen (N). Furthermore, three rules were established for CBZ decarbonization and N removal during degradation, observing the transformation of aromatic compounds into aliphatic hydrocarbons and stable N-containing organic matter over time. Five potentially highly toxic BPs were screened from 14 identified BPs, with toxicity predictions guiding the selection of commercial standards for quantification and true toxicity testing. Additionally, BP207 emerged as the most toxic, supported by the predictive toxicity accumulation model (PTAM). Notably, highly toxic BPs feature an acridine structure, indicating its significant contribution to toxicity. These findings offered valuable insights into the degradation mechanisms of emerging contaminants and the biosafety of aquatic environments during deep oxidation.

Enhanced inactivation of Escherichia coli through hydrogen peroxide decomposition assisted by nanoscale cupric oxide-decorated activated carbon

In this study, nanoscale cupric oxide-decorated activated carbon (nCuO@AC) was synthesized by impregnation-calcination and employed to assist the decomposition of H2O2 for effective sterilization with Escherichia coli as target bacteria. Characteristic technologies demonstrated that copper oxide particles of 50-100 nm were uniformly distributed on AC surface. Owing to electron transfer from hydroxyl and aldehyde to CuO on AC, surface-bonded Cu(II) was partially reduced to Cu(I) in the nCuO matrix. The resultant Cu(I) expedited the decomposition of H2O2 and converted it into ·OH radicals which were identified by quenching experiment and electron paramagnetic resonance test. Due to oxidation attack of generated ·OH, the nCuO@AC-H2O2 system achieved a much higher inactivation rate of 6.0 log within 30 min as compared to those of 2.1 and 1.3 log in the nCuO@AC and nCuO-H2O2 systems. It also exhibited excellent pH adaptability and high inactivation efficiency under neutral conditions. After four cycles, the nCuO@AC-H2O2 system could still inactivate 5.5 log bacteria, indicating excellent stability and reusability of nCuO@AC. Spent nCuO@AC could be regenerated by eluting surficial copper oxides with hydrochloric acid, and re-coating nCuO particles through impregnation-calcination with a regeneration rate of 96.6%. Our results demonstrated that nCuO@AC was an efficient and prospective catalyst to assist the decomposition of H2O2 for effective inactivation of bacteria in water.

In silico ecotoxicity assessment of pharmaceutical residues in wastewater following oxidative treatment

Advanced oxidation processes such as thermal plasma activation and UV-C/H2O2 treatment are considered as applications for the degradation of pharmaceutical residues in wastewater complementary to conventional wastewater treatment. It is supposed that direct oxidative treatment can lower the toxicity of hospital sewage water (HSW). The aim of this study was to predict the ecotoxicity for three aquatic species before and after oxidative treatment of 10 quantified pharmaceuticals in hospital sewage water. With the application of oxidative chemistry, pharmaceuticals are degraded into transformation products before reaching complete mineralization. To estimate the potential ecotoxicity for fish, Daphnia and green algae ECOSAR quantitative structure-activity relationship software was used. Structure information from pristine pharmaceuticals and their oxidative transformation products were calculated separately and in a mixture computed to determine the risk quotient (RQ). Calculated mixture toxicities for 10 compounds found in untreated HSW resulted in moderate-high RQ predictions for all three aquatic species. Compared to untreated HSW, 30-min treatment with thermal plasma activation or UV-C/H2O2 resulted in lowered RQs. For the expected transformation products originating from fluoxetine, cyclophosphamide and acetaminophen increased RQs were predicted. Prolongation of thermal plasma oxidation up to 120 min predicted low-moderate toxicity in all target species. It is anticipated that further degradation of oxidative transformation products will end in less toxic aliphatic and carboxylic acid products. Predicted RQs after UV-C/H2O2 treatment turned out to be still moderate-high. In conclusion, in silico extrapolation of experimental findings can provide useful predicted estimates of mixture toxicity. However due to the complex composition of wastewater this in silico approach is a first step to screen for ecotoxicity. It is recommendable to confirm these predictions with ecotoxic bioassays.

Effect of Persulfate Activation by Electrogenerated H2O2 and Anodic Oxidation on the Color Removal of Dye Solutions at Pt and BDD Anodes

In this study, tartrazine solutions were oxidized using innovative electrochemical advanced oxidation processes (EAOPs) that combined persulfate (PS) activation with electrogenerated H₂O₂, cathodic reduction and anodic oxidation at Pt and BDD anodes, and graphite cathode in an undivided stirred reactor. For the Pt anode, SO₄·^- was generated from a reduction reaction at the cathode and a reaction between the PS and electrogenerated H₂O₂. For the BDD anode, SO₄·^- was generated from a reduction reaction at the cathode, an oxidation reaction at the anode, and a reaction between PS and electrogenerated H₂O₂. Among these activation methods, the activation efficiency of PS by electrogenerated H₂O₂ is much better than other methods. The effects of PS concentration up to 36 mM, applied current density between 6 to 15 mA cm^-2, and temperatures between 25 to 45 °C were investigated. For the electro-Fenton process with Pt anode (Pt-H₂O₂/PS process), the best result for oxidizing 250 mg L^-1 tartrazine solution was obtained with 37.5 mM Na₂SO₄ + 9.0 mM Na₂S₂O₈, applied current density at 12 mA cm^-2 and 45 °C, acquiring total color removal after 30 min reaction. For the electro-Fenton process with BDD anode (BDD-H₂O₂/PS process), the best result for oxidizing 250 mg L^-1 tartrazine solution was obtained with 25 mM Na₂SO₄ + 18 mM Na₂S₂O₈, applied current density at 12 mA cm^-2 and 45 °C, yielding 100% color removal after 30 min reaction. The main oxidizing agents are SO₄·^- and OH· in the anodic oxidation process with PS and the electro-Fenton process with PS. It is concluded that the additions of PS tremendously improve the oxidation power of electro-Fenton processes with PS, especially the Pt-H₂O₂/PS process.

FeS2/carbon felt as an efficient electro-Fenton cathode for carbamazepine degradation and detoxification: In-depth discussion of reaction contribution and empirical kinetic model

Carbamazepine (CBZ) decay by electro-Fenton (EF) oxidation using a novel FeS₂/carbon felt (CF) cathode, instead of a soluble iron salt, was studied with the aim to accelerate the reaction between H₂O₂ and ferrous ions, which helps to produce more hydroxyl radicals (^•OH) and eliminate iron sludge. First, fabricated FeS₂ and its derived cathode were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Anodes were then screened, with DSA (Ti/IrO₂-RuO₂) showing the best performance under EF oxidation regarding CBZ degradation and electrochemical characterization. Several operating parameters of this EF process, such as FeS₂ loading, current density, gap between electrodes (GBE), initial [CBZ], and electrolyte type, were also investigated. Accordingly, a nonconsecutive empirical kinetic model was established to predict changes in CBZ concentration under the given operational parameters. The contribution of different oxidation types to the EF process was calculated using kinetic analysis and quenching experiments to verify the role of the FeS₂-modified cathode. The reaction contributions of anodic oxidation (AO), H₂O₂ electrolysis (EP), and EF oxidation to CBZ removal were 12.81%, 7.41%, and 79.77%, respectively. The ^•OH exposure of EP and EF oxidation was calculated, confirming that ^•OH exposure was approximately 22.45-fold higher using FeS₂-modified CF. Finally, the 19 intermediates formed by CBZ degradation were identified by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. Accordingly, four CBZ degradation pathways were proposed. ECOSAR software was used to assess the ecotoxicity of intermediates toward fish, daphnia, and green algae, showing that this novel EF oxidation process showed good toxicity reduction performance. A prolonged EF retention time was proposed to be necessary to obtain clean and safe water, even if the targeted compound was removed at an earlier time.

Dinitrodiazophenol industrial wastewater treatment by a sequential ozone Fenton process

The ozonation process is efficient in degrading aromatic substances and substances with unsaturated bonds, but cannot effectively destroy small-molecule organic compounds, which accumulate. Likewise, the Fenton process is a classic wastewater treatment method, but requires strict pH control and produces secondary pollution when the concentration of organic substances is high. In this study, we applied a 1stO₃-2ndFenton sequential process to treat diazodinitrophenol (DDNP) industrial wastewater and provide suitable reaction conditions for Fenton process. For the 1stOzone process, organics removal increased as O₃ dosage increased. At optimized operation, the 1stO₃ process provided an acidic effluent (pH = 3) and reduced the organics concentration to a level suitable for the 2ndFenton process. Benzene ring substances as well as nitro group and diazo group compounds were greatly degraded in the 1stO₃ process and were further mineralized in the 2ndFenton process. Additionally, the biodegradability of DDNP industrial wastewater was greatly improved. This is the first reported time that ozonation and the Fenton process have been integrated sequentially to treat an explosive production wastewater. The study provides a feasible chemical oxidation method for treating DDNP industrial wastewater by simply combining two classic treatment processes.

Decomplexation removal of Ni(II)-citrate complexes through heterogeneous Fenton-like process using novel CuO-CeO2-CoOx composite nanocatalyst

A novel CuO-CeO₂-CoO_x nanocatalyst was prepared for heterogeneous Fenton-like reaction to break the Ni²⁺-chelate into free Ni²⁺ in electroless nickel plating wastewater, followed by separation of Ni²⁺ in an insoluble form. The composite nanocatalysts prepared by co-precipitation method were characterized by XRD, TEM, and XPS, et al. Its catalytic activity as Fenton-like reagent was evaluated by the removal efficiency of Ni(II)-citrate after decomplexation and postprecipitation treatment. Subsequently, the effects of operating parameters on the decomplexation efficiency of the nanocatalysts were investigated including calcination temperature of catalysts, H₂O₂ concentration, catalyst dosage, initial pH and reaction temperature. Under optimized condition, the Ni(II)-citrate complexes (C₀ = 1.0 mM) achieved the complete decomplexation (>99.9%) within 60-min reaction using 0.3 g/L of CuO-CeO₂-CoO_x calcined at 450 °C and 75 mM of H₂O₂ at pH 3.0 under 50 °C of reaction. Then, Ni²⁺ after decomplexation could be completely removed by the subsequent precipitation at pH 11.0. In addition, the life test of CuO-CeO₂-CoO_x catalyst indicated that, after recycled 10 times, its activity for decomplexation of Ni(II)-citrate decreased no more than 8%. As a result, this new heterogeneous Fenton-like process is promising for decomplexation and purification of electroless nickel plating wastewater as a sludge reduction technology.