Photoelectrocatalytic oxidation of chlortetracycline using Ti/TiO2 photo-anode with simultaneous H2O2 production

Degradation of typical tetracycline antibiotics in landfill leachate by three-dimensional aerated electrocatalytic reactor (3D-AER): electrode properties, influencing factors and degradation mechanism

Anode Ti/RuO2/IrO2-SnO2 was prepared, and coconut shell biochar (CBC) was applied as the particle electrode to construct a three-dimensional aerated electrocatalytic reactor (3D-AER) for enhanced treatment of landfill leachate, especially for tetracycline antibiotics (TCs), including tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) in it. The characterization results of the anode indicated that the dense RuO2-IrO2-SnO2 solid solution on the surface of the electrode coating had excellent electrocatalytic activity, high oxygen evolution potential, and low chlorine evolution potential. The investigation of influencing factors showed that under the conditions of pH 10, current density of 30 mA/cm2, KCl concentration of 100 mg/L, CBC dosage of 7 g/L, CBC particle size of 1.7-2.36 mm, and electrode spacing of 3 cm, excellent treatment effects were achieved for nitrogen and carbon removal from leachate. The removal rates of COD, NH3-N, TC, OTC, and CTC reached 82.76 %, 66.02 %, 86.58 %, 87.46 %, and 81.88 %, respectively, and the degradation process of TCs followed pseudo-first-order kinetics. The presence of CBC enhanced mass transfer and electrolysis efficiency, promoting the generation of ·OH. The degradation modes of macromolecular organic compounds and TCs in leachate included anodic direct oxidation and indirect oxidation (free radical pathway(·OH) and non-free radical pathway (1O2 and active chlorine)), among which 1O2 dominated. In the denitrification process, NH3-N accounted for 79.69 % of TN, most of which was converted into N2 and NO3-, and Cl· and active chlorine played an indispensable role. Therefore, this study shares a theoretical basis for further understanding the electrocatalytic process, degradation mechanism of TCs in chlorine containing leachate.

Visible-light photoelectrocatalysis/H2O2 synergistic degradation of organic pollutants by a magnetic Fe3O4@SiO2@mesoporous TiO2 catalyst-loaded photoelectrode

In this paper, we describe a method for photoelectrocatalysis (PEC)/H₂O₂ synergistic degradation of organic pollutants with a magnetic Fe₃O₄@SiO₂@mesoporous TiO₂ (FST) photocatalyst-loaded electrode. At optimal conditions of pH 3.0, 2.25% H₂O₂, working electrode (fixed FST 30 mg) potential +0.6 V (vs. SCE), and 10 mg L^-1 of all experimental pollutants, the FST PEC/H₂O₂ synergistic system exhibited high activity and stability for the removal of various organic pollutants under visible light with comparable degradation efficiencies, including MB (98.8%), rhodamine B (Rh B, 96.7%), methyl orange (MO, 97.7%), amoxicillin (AMX, 83.9%). Moreover, this system obtained TOC removal ratios of 83.5% (MB), 77.9% (Rh B), 80.2% (MO), 65.5% (AMX) within 8 min. The kinetic rate constants of the PEC/H₂O₂ synergistic system were nearly 53 and 1436 times higher than that of the PEC process and H₂O₂ photolysis under visible light, respectively. Furthermore, the main reactive oxidant species (˙OH, ˙O₂ ^-) were studied and enhanced mechanisms of the photocatalytic-electro-H₂O₂ coupling system were proposed. This work brings new insights to efficiently purify organic pollutants by PEC coupled with peroxide under solar light illumination.

Recent advances on inactivation of waterborne pathogenic microorganisms by (photo) electrochemical oxidation processes: Design and application strategies

Compared with other conventional water disinfection processes, (photo) electrochemical oxidation (P/ECO) processes have the characteristics of environmental friendliness, convenient installation and operation, easy control and high efficiency of inactivating waterborne pathogenic microorganisms (PMs), so that more and more research work has been focused on this topic, but there is still a huge gap between the research and practical application. Here, the research network of inactivating PMs by P/ECO processes has been comprehensively summarized, and the electrode/reactor/process design strategies based on strengthening direct and indirect oxidation, enhancing mass transfer efficiency and electron transfer efficiency, and improving the effective dose of electrogenerated oxidants are discussed. Furthermore, the factors affecting the inactivation of PMs and the issues regarding to stability and lifetime of the electrode are discussed respectively. Finally, the important research priorities and possible research challenges of P/ECO processes are put forward to make significant progress of this technology.

Study of the performance of a cylindrical flow-through electro-Fenton reactor using different arrangements of carbon felt electrodes: effect of key operating parameters

In this work, a cylindrical flow-through electro-Fenton reactor containing graphite felt electrodes and an Fe(II) loaded resin was evaluated for the production of the Fenton reaction mixture and for the degradation of amoxicillin (AMX) and fecal coliforms containing aqueous solutions. First, the influence of several factors such as treatment time, current intensity, flow rate, and electrode position was investigated for the electrogeneration of H₂O₂ and the energetic consumption by means of a factorial design methodology using a 2⁴ factorial matrix. Electric current and treatment time were found to be the pivotal parameters influencing the H₂O₂ production with contributions of 40.2 and 26.9%, respectively. The flow rate had low influence on the responses; however, 500 mL min^-1 (with an average residence time of 1.09 min obtained in the residence time distribution analysis) allowed to obtain a better performance due to the high mass transport to and from the electrodes. As expected, polarization was also found to play an important role, since for the cathode-to-anode flow direction, lower H₂O₂ concentrations were observed when compared with the anode-to-cathode flow arrangement, indicating that part of the H₂O₂ produced in the cathode was destroyed at the anode. A fluorescence study of hydroxyl radical production, on the other hand, showed that higher yields were obtained using an anode-to-cathode flow direction (up to 3.88 µM), when compared with experiments carried out using a cathode-to-anode flow path (3.11 µM). The removal of a commercial formulation of the antibiotic AMX was evaluated in terms of total organic carbon, achieving up to 57.9% and 38.63% of pollutant mineralization using synthetic and real sanitary wastewater spiked, respectively. Finally, the efficiency of the process on the inactivation of fecal coliforms in sanitary wastewater samples was assessed, reducing 90% of the bacteria after 5 min of electrolysis.

Solar-driven photoelectrocatalytic degradation of anticancer drugs using TiO2 nanotubes decorated with SnS quantum dots

In recent years, the growing interest in applying photoelectrocatalysis (PEC) to decompose organic pollutants has resulted in the need to search for new photoelectrode materials with high activity under visible light radiation. The presented research showed an increased photoelectrocatalytic activity under sunlight of Ti/TiO₂ sensitized with SnS quantum dots, obtained by the successive ionic layer adsorption and reaction (SILAR) method. The presence of SnS caused the enhanced absorption of visible irradiation and the reduction of recombination of generated charges by a p-n heterojunction created with the TiO₂. The highest efficiency of photoelectrocatalytic degradation of anticancer drugs (ifosfamide, 5-fluorouracil, imatinib) was achieved for the SnS-Ti/TiO₂ photoelectrode with a SnS quantum dot size from 4 to 10 nm. In addition, a decrease of IF PEC degradation efficiency was observed with increasing pH and with the presence of Cl^-, NO₃^-, HCO₃^- and organic matter in the treated solution. Studies of the PEC mechanism have shown that drug degradation occurs mainly as a result of the direct and indirect action of photogenerated holes on the SnS-Ti/TiO₂ photoelectrode, and the identified degradation products allowed for the presentation of the degradation pathway of IF, 5-FU and IMB. Duckweed (Lemna minor) growth inhibition tests showed no toxicity of the drug solutions after treatment.

Fundamentals and applications of photoelectrocatalysis as an efficient process to remove pollutants from water: A review

Water pollution is an environmental problem in constant raising because of population growing, industrial development, agricultural frontier expansion, and principally because of the lack of wastewater treatment technology to remove organic recalcitrant and toxic pollutants from industrial and domestic wastewater. Recalcitrant compounds are a serious environmental and health problem mainly due to their toxicity and potential hazardous effects on living organisms, including human beings. Conventional wastewater treatments have not been able to remove efficiently pollutants from water; however, electrochemical advanced oxidation processes (EAOPs) are able to solve this environmental concern. One of the most recent EAOPs technology is photoelectrocatalysis (PEC), it consists in applying an external bias potential to a semiconductor film placed over a conductive substrate to avoid the recombination of photogenerated electron-hole (e^-/h⁺) pairs, increasing h⁺ availability and hydroxyl radicals' formation, responsible for promoting the degradation/mineralization of organic pollutants in aqueous medium. This review summarizes the recent advances in PEC as a promising technology for wastewater treatment. It addresses the fundamentals and kinetic aspects of PEC. An analysis of photoanode materials and of the configuration of photoelectrochemical reactors is also presented, including an analysis of the influence of the main operational parameters on the treatment of contaminated water. Finally, the most recent applications of PEC are reviewed, and the challenges and perspectives of PEC in wastewater treatment are discussed.

Treatment of real wastewater by photoelectrochemical methods: An overview

An inadequate and inefficient performance ability of conventional methods to remove persistent organic pollutants urges the need of alternative or complementary advanced wastewater treatments methods to ensure the safer reuse of reclaimed water. Photoelectrochemical methods are emerging as promising options among other advanced oxidation processes because of the higher treatment efficiency achieved due to the synergistic effects of combined photochemical and electrolysis reactions. Synergistic effects of integrated photochemical, electrochemical and photoelectrochemical processes not only increase the hydroxyl radical production; an enhancement on the mineralization ability through various side reactions is also achieved. In this review, fundamental reaction mechanisms of different photoelectrochemical methods including photoelectrocatalysis, photo/solar electro-Fenton, photo anodic oxidation, photoelectroperoxone and photocatalytic fuel cell are discussed. Various integrated photochemical, electrochemical and photoelectrochemical processes and their synergistic effects are elaborated. Different reactor configurations along with the positioning of electrodes, photocatalysts and light source of the individual/combined photoelectrochemical treatment systems are discussed. Modified photoanode and cathode materials used in the photoelectrochemical reactors and their performance ability is presented. Photoelectrochemical treatment of real wastewater such as landfill leachate, oil mill, pharmaceutical, textile, and tannery wastewater are reviewed. Hydrogen production efficiency in the photoelectrochemical process is further elaborated. Cost and energy involved in these processes are briefed, but the applicability of photocatalytic fuel cells to reduce the electrical dependence is also summarised. Finally, the use of photoelectrochemical approaches as an alternative for treating soil washing effluents is currently discussed.

Photo-assisted electrochemical advanced oxidation processes for the disinfection of aqueous solutions: A review

Disinfection is usually the final step in water treatment and its effectiveness is of paramount importance in ensuring public health. Chlorination, ultraviolet (UV) irradiation and ozone (O3) are currently the most common methods for water disinfection; however, the generation of toxic by-products and the non-remnant effect of UV and O3 still constitute major drawbacks. Photo-assisted electrochemical advanced oxidation processes (EAOPs) on the other hand, appear as a potentially effective option for water disinfection. In these processes, the synergism between electrochemically produced active species and photo-generated radicals, improve their performance when compared with the corresponding separate processes and with other physical or chemical approaches. In photo-assisted EAOPs the inactivation of pathogens takes place by means of mechanisms that occur at different distances from the anode, that is: (i) directly at the electrode's surface (direct oxidation), (ii) at the anode's vicinity by means of electrochemically generated hydroxyl radical species (quasi-direct), (iii) or at the bulk solution (away from the electrode surface) by photo-electrogenerated active species (indirect oxidation). This review addresses state of the art reports concerning the inactivation of pathogens in water by means of photo-assisted EAOPs such as photo-electrocatalytic process, photo-assisted electrochemical oxidation, photo-electrocoagulation and cathodic processes. By focusing on the oxidation mechanism, it was found that while quasi-direct oxidation is the preponderant inactivation mechanism, the photo-electrocatalytic process using semiconductor materials is the most studied method as revealed by numerous reports in the literature. Advantages, disadvantages, trends and perspectives for water disinfection in photo-assisted EAOPs are also analyzed in this work.

Microwave-induced release and degradation of airborne antibiotic resistance genes (ARGs) from Escherichia coli bioaerosol based on microwave absorbing material

Antibiotic resistance genes (ARGs) have been detected in the atmosphere. Airborne ARGs transmission threatens human health. In the present study, we investigated the release and degradation of airborne ARGs from Escherichia coli bioaerosol through microwave (MW) irradiation. In this study, a new MW absorbing material (Fe₃O₄@SiC ceramic foam) that contributed to its stronger MW absorption is presented. When the MW input energy density was 7.4 × 10³ kJ/m³, the concentration of airborne Escherichia coli decreased by 4.4 log. Different DNA forms were found in the air because MW irradiation ruptured cell membranes. The bound particles provide more protection for bound DNA in the degradation process than free DNA. After the self-degradation of the released airborne free ARGs, some of them would remain and continue to spread in the atmosphere. The released airborne free ARGs cannot be ignored. Total ARGs concentrations decrease rapidly with increased temperature. The inactivation rate constant of ARGs through MW irradiation is higher than that through the Fenton and UV, however, the energy efficiency per order of MW irradiation is lower. Therefore, MW irradiation with Fe₃O₄@SiC ceramic foam could efficiently degrade the distribution of ARGs in the atmosphere.

Gas-Phase Photoelectrocatalytic Oxidation of NO via TiO2 Nanorod Array/FTO Photoanodes

Most photoelectrocatalytic (PEC) reactions are performed in the liquid phase for convenient electron transfer in an electrolyte solution. Herein, a novel PEC reactor involving a tandem combination of TiO₂ nanorod array/fluorine-doped tin oxide (TiO₂-NR/FTO) working electrodes and an electrochemical auxiliary cell was constructed to drive the highly efficient PEC oxidation of indoor gas (NO_x). With the aid of a low bias voltage (0.3 V), the as-formed PEC reactor exhibited an 80% removal rate for oxidizing NO (500 ppb) under light irradiation, which is much higher than that of the traditional photocatalytic (PC) process. Upon being irradiated by light, the photogenerated electrons are quickly separated from the holes and transferred to the counter electrode (Pt) owing to the applied bias voltage, leaving photogenerated holes in the TiO₂-NR/FTO electrode for oxidizing NO molecules. Moreover, both dry and humid NO could be effectively removed by the tandem TiO₂-NR/FTO-based gas-phase PEC reactor, indicating that the NO molecules could also be directly oxidized by photogenerated holes in addition to hydroxyl radicals. The presence of trace amounts of water could promote the PEC oxidation of NO owing to the formation of hydroxyl radicals induced by reactions between the water and holes, which could further oxidize NO. This PEC reactor offers an energy-saving, environmentally friendly, and efficient route to treat air polluted with low concentrations of gases (NO_x and SO_x).

Semiconductor Electrode Materials Applied in Photoelectrocatalytic Wastewater Treatment—an Overview

Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable raw materials. Conventional sewage treatment systems are often not efficient enough for the complete degradation of pollutants and they are characterized by high energy consumption. Moreover, the chemical energy that is stored in the wastewater is wasted. A solution to these problems is an application of photoelectrocatalytic treatment methods, especially when they are coupled with energy generation. The paper presents a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants. The fundamentals of photoelectrocatalytic reactions and the mechanism of pollutants treatment as well as parameters affecting the treatment process are presented. Examples of different semiconductor photoelectrodes that are applied in treatment processes are described in order to present the strengths and weaknesses of the photoelectrocatalytic treatment of industrial wastewater. This overview is an addition to the existing knowledge with a particular focus on the main experimental conditions employed in the photoelectrocatalytic degradation of various pollutants with the application of semiconductor photoelectrodes.

Comparison of ciprofloxacin degradation in reclaimed water by UV/chlorine and UV/persulfate advanced oxidation processes

This study analyzed the ciprofloxacin (CIP) degradation in real reclaimed water through UV/chlorine and UV/persulfate (UV/PS) advanced oxidation processes. The influence of oxidant dosage, pH, inorganic anions, and humic acid (HA) on the oxidation capacity and performances of various UV-based processes was investigated. The results revealed that the CIP degradation rate constants in the UV/chlorine and UV/PS processes were higher than that in UV/H₂ O₂ , direct-UV, NaClO, and K₂ S₂ O₈ processes. The removal rate peaked at 0.1 mM oxidant dosage for 1 μM CIP, while the rate constant was highest at pH 5 (UV/chlorine) and pH 7 (UV/PS). The presence of Cl^- , HCO₃ ^- , and HA inhibited CIP removal in both processes. The degradation rate observed in reclaimed water was high, but still lower than that in laboratory water by 9.2 (UV/chlorine) and 9 (UV/PS) times. The UV/chlorine and UV/PS processes were found to be more cost-effective and hence more feasible in removing refractory compounds in reclaimed water. PRACTITIONER POINTS: The addition of oxidant and UV irradiation together had a pronounced promotion in the degradation of CIP. Cl^· and SO₄ ^·- had potential importance for enhancing CIP degradation in UV/chlorine and UV/PS process, respectively. UV/chlorine and UV/PS processes exhibited effective removal capability to CIP in real reclaimed water.

Synthesis of a Novel Catalyst MnO/CNTs for Microwave-Induced Degradation of Tetracycline

Microwave-induced catalytic degradation (MICD) has been considered as one of the most prospective approaches to remove organic contaminants from water. High-performance catalysts, ideally offering efficient degradation ability, are essential to this process. This work reports the fabrication of manganese oxide on carbon nanotubes (MnO/CNTs) as an efficient catalyst under microwave irradiation (MI) to remove tetracycline (TC) from aqueous solution. The hybrid MnO/CNTs structure shows excellent performance in TC degradation. Combining experimental characterization and theoretical calculations, synergistic mechanisms are revealed: (i) Strong MnO/CNTs interaction stabilizes Mn(II) through interfacial bonding; (ii) high-spin states associated with low coordinated Mn(II) play a major role in MICD; and (iii) superoxide radicals (•O2−) and hydroxyl radicals (•OH) induced by microwave input are identified as the major active species.

H2O2-assisted photoelectrocatalytic degradation of Mitoxantrone using CuO nanostructured films: Identification of by-products and toxicity

CuO nanostructured thin films supported on silicon with 6.5 cm² area (geometric area greater than the studies reported in the literature) were synthesized by a chemical bath deposition technique. The electrodes were characterized by MEV, XRD, XPS, contact angle, cyclic voltammetry and electrochemical impedance spectroscopy analyses. To evaluate the photoelectrochemical properties of the CuO films, photocurrent-voltage measurements were performed using linear voltammetry. The catalytic activities of CuO nanostructures were evaluated by monitoring photodegradation of Mitoxantrone (MTX) under UV-A light irradiation. The method of photoelectrocatalysis (PEC), applying a voltage of 1.5 V and assisted by adding H₂O₂, was undertaken. To the best of our knowledge, no studies on the degradation of anticancer agents using PEC process have been found in the literature. For comparison purposes, experiments were performed under the same conditions by assisted photocatalysis (PC) with H₂O₂ and direct photolysis. CuO deposits consist of a needle-like morphology. The presence of CuO in the tenorite phase was evidenced by XRD and the XPS spectra showed the presence of copper(II) oxide. The increase in current under illumination shows that CuO exhibits photoactivity. The PEC system showed a 75% level of MTX degradation, while the level achieved using PC was 50%. Under UV-A light alone only 3% removal was obtained after 180 min. Up to 10 by-products were identified by chromatography-mass spectrometry (LC-MS) with m/z values ranging between 521 and 285 and a plausible degradation route has been proposed. It is worth mentioning that 9 by-products identified in this work, were not found in the literature in other studies of degradation or products generated as metabolites. The toxicity tests of MTX before and after PEC treatment with Artemia Salina and Allium cepa showed a decrease in the acute toxicity of the medium as the antineoplastic was degraded.

Simultaneous efficient adsorption and accelerated photocatalytic degradation of chlortetracycline hydrochloride over novel Fe-based MOGs under visible light irradiation assisted by hydrogen peroxide

Two novel porous MOGs were prepared for degrading CTC, and JLUE-MOG-1 exhibited an enhanced performance because of the photo-Fenton synergistic effect.

Application of ZnO-Ag-Nd nanocomposite as a new synthesized nanophotocatalyst for the degradation of organic compounds: kinetic, thermodynamic and economic study

In the present research, a zinc oxide (ZnO)-silver (Ag)-neodymium (Nd) nanocomposite was synthesized via the combustion method for the degradation of dyes as organic pollutants. The synthesized nanophotocatalyst was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques. The process of organic pollutant (Acid Red 18) removal was carried out in a semi-batch photoreactor equipped with an ultraviolet lamp. Also, the influence of key operational parameters such as pH, temperature, initial concentration of solution, and nanophotocatalyst dosage was investigated to evaluate kinetic and thermodynamic properties. Under optimum process conditions (pH = 6.21, dosage of nanophotocatalyst = 0.08 g/l, and low initial concentration of the solution), degradation of pollutant was monitored by measuring the total organic carbon of the solution. Finally, an economic study showed that the photocatalytic advanced oxidation process is an viable treatment method for low concentrations of organic pollutants.

Anchoring Fe3O4 Nanoparticles on Carbon Nanotubes for Microwave-Induced Catalytic Degradation of Antibiotics

Microwave-induced catalytic degradation is considered amongst the most efficient techniques to remove antibiotic such as chlortetracycline from contaminated water. Described here is a new microwave-induced oxidation catalyst based on carbon nanotubes (CNTs) decorated uniformly with nanoparticles of Fe₃O₄. The combination of dielectric loss and magnetic loss of the material contributed to its stronger microwave absorption and the ability to produce more "hot spots". These hot spots promoted the oxidation of common antibiotics such as chlortetracycline, tetracycline, and oxytetracycline under microwave irradiation. Experiments with the addition of scavenger showed that hydroxy radicals (^•OH) together with superoxide radicals (^•O₂^-) contributed to the antibiotics removal as well. The final degradation products included CO₂ and NO₃^- as confirmed by mass spectroscopy and ion chromatography analyses. The results indicated that the Fe₃O₄/CNTs was an efficient catalyst for microwave-induced oxidation.

Evaluating tetracycline degradation pathway and intermediate toxicity during the electrochemical oxidation over a Ti/Ti4O7 anode

Tetracycline (TC) is one of the most widely used antibiotics with significant impacts on human health and thus it needs appropriate approaches for its removal. In the present study, we evaluated the performance and complete pathway of the TC electrochemical oxidation on a Ti/Ti₄O₇ anode prepared by plasma spraying. Morphological data and composition analysis indicated a compact coating layer on the anode, which had the characteristic peaks of Ti₄O₇ as active constituent. The TC electrochemical oxidation on the Ti/Ti₄O₇ anode followed a pseudo-first-order kinetics, and the TC removal efficiency reached 95.8% in 40 min. The influential factors on TC decay kinetics included current density, anode-cathode distance and initial TC concentration. This anode also had high durability and the TC removal efficiency was maintained over 95% after five times reuse. For the first time, we unraveled the complete pathway of the TC electrochemical oxidation using high-performance liquid chromatograph (HPLC) and gas chromatograph (GC) coupled with mass spectrometer (MS). ·OH radicals produced from electrochemical oxidation attack the double bond, phenolic group and amine group of TC, forming a primary intermediate (m/z = 461), secondary intermediates (m/z = 432, 477 and 509) and tertiary intermediates (m/z = 480, 448 and 525). The latter were further oxidized to the key downstream intermediate (m/z = 496), followed by further downstream intermediates (m/z = 451, 412, 396, 367, 351, 298 and 253) and eventually short-chain carboxylic acids. We also evaluated the toxicity change during the electrochemical oxidation process with bioluminescent bacteria. The bioluminescence inhibition ratio peaked at 10 min (55.41%), likely owing to the high toxicity of intermediates with m/z = 461, 432 and 477 as obtained from quantitative structure activity relationship (QSAR) analysis. The bioluminescence inhibition ratio eventually decreased to 16.78% in 40 min due to further transformation of TC and intermediates. By comprehensively analyzing the influential factors and complete degradation pathway of TC electrochemical oxidation on the Ti/Ti₄O₇ anode, our research provides deeper insights into the risk assessment of intermediates and their toxicity, assigning new perspectives for practical electrochemical oxidation to effectively eliminate the amount and toxicity of TC and other antibiotics in wastewater.

Evaluation of UV/S2O8 process efficiency for removal of metronidazole (MNZ) from aqueous solutions

Antibiotics are known today as emerging contaminants due to potentially adverse effects on aquatic ecosystems and the health of humans and animals, even at very low concentrations. The present study was conducted to evaluate the efficiency of the UV/S₂O₈ process and affecting factors (pH, initial metronidazole (MNZ) concentration, initial persulfate concentration and reaction time) in removing antibiotic MNZ. The results obtained from the experiments showed that the UV/S₂O₈ process efficiency is higher in acidic pH values due to production of further radical SO₄^- and increases with extended contact time, but the efficiency of the process is reduced by increasing the concentration of MNZ. In assessing the effect of initial persulfate concentration on the process efficiency, MNZ removal efficiency was also increased by 99.5% after contact time of 35 min with increasing the initial persulfate concentration up to 1 g/L. However, the process efficiency was decreased at higher concentrations (2 mg/L) due to reaction of sulfate radicals with each other or with persulfate and its saturation. The kinetic data fitted the pseudo-first-order kinetic model (R² > 99%). The findings of this study clearly demonstrated the high potential of the UV/S₂O₈ process in the degradation of MNZ.

Understanding Toxicity of Nanomaterials in Biological Systems

Nanotechnology is a growing applied science having considerable global socioeconomic value. Nanoscale materials are casting their impact on almost all industries and all areas of society. A wide range of engineered nanoscale products has emerged with widespread applications in fields such as energy, medicine, electronics, plastics, energy and aerospace etc. While the market for nanotechnology products will have grown over one trillion US dollars by 2015, the presence of these material is likely to increase leading to increasing likelihood of exposure. The direct use of nanomaterials in humans for medical and cosmetic purposes dictates vigorous safety assessment of toxicity. Therefore this book chapter provides the detailed toxicity assessment of various types of nanomaterials.

Preparation of Cathode-Anode Integrated Ceramic Filler and Application in a Coupled ME-EGSB-SBR System for Chlortetracycline Industrial Wastewater Systematic Treatment

Chlortetracycline (CTC) contamination of aquatic systems has seriously threatened the environmental and human health throughout the world. Conventional biological treatments could not effectively treat the CTC industrial wastewater and few studies have been focused on the wastewater systematic treatment. Firstly, 40.0 wt% of clay, 30.0 wt% of dewatered sewage sludge (DSS), and 30.0 wt% of scrap iron (SI) were added to sinter the new media (cathode-anode integrated ceramic filler, CAICF). Subsequently, the nontoxic CAICF with rough surface and porous interior packed into ME reactor, severing as a pretreatment step, was effective in removing CTC residue and improving the wastewater biodegradability. Secondly, expanded granular sludge bed (EGSB) and sequencing batch reactor (SBR), serving as the secondary biological treatment, were mainly focusing on chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal. The coupled ME-EGSB-SBR system removed about 98.0% of CODcr and 95.0% of NH3-N and the final effluent met the national discharged standard (C standard of CJ 343-2010, China). Therefore, the CTC industrial wastewater could be effectively treated by the coupled ME-EGSB-SBR system, which has significant implications for a cost-efficient system in CTC industrial systematic treatment and solid wastes (DSS and SI) treatment.

One-pot solvothermal synthesis of magnetic SnFe2O4 nanoparticles and their performance in the photocatalytic degradation of chlortetracycline with visible light radiation

Highly crystalline SnFe₂O₄ nanoparticles with high saturation magnetization and superior chlortetracycline degradation efficiency was developed using a one-pot solvothermal method.

Removal of carbamazepine from spiked municipal wastewater using electro-Fenton process

The electrochemical degradation of carbamazepine (CBZ) in both synthetic solutions (CBZo = 12 mg/L) and enriched municipal effluents (CBZo = 60-70 μg/L) was investigated using an electro-Fenton (EF) process. Different operating parameters were investigated, including current intensity, pH, reaction time, ferrous ion concentration, and the type of anode material. The current intensity, the type of anode material, and the concentration of ferrous ions played an important role in the CBZ degradation efficiency. The degradation was mainly attributed to direct anodic oxidation. The best operating conditions for the synthetic sample were obtained at a current density of 0.2 A, a pH of 3.0, and 120 min of treatment using a boron-doped diamond (BDD) anode in the presence of 0.25 mM of Fe(2+). Under these conditions, 52% of total organic carbon (TOC) and 73% of CBZ were removed. The process was also tested as tertiary treatment for a municipal wastewater treatment plant effluent, and CBZ was completely removed.

Effect of oxidants on photoelectrocatalytic decolourization using α-Fe2O3/TiO2/activated charcoal plate nanocomposite under visible light

Effect of oxidants on the decolourization efficiency of Lanasol Yellow 4G in photoelectrocatalytic process using α-Fe₂O₃/TiO₂/ACP nanocomposite under visible light.

Mechanistic understanding of toxicity from nanocatalysts

Nanoparticle-based catalysts, or nanocatalysts, have been applied in various industrial sectors, including refineries, petrochemical plants, the pharmaceutical industry, the chemical industry, food processing, and environmental remediation. As a result, there is an increasing risk of human exposure to nanocatalysts. This review evaluates the toxicity of popular nanocatalysts applied in industrial processes in cell and animal models. The molecular mechanisms associated with such nanotoxicity are emphasized to reveal common toxicity-inducing pathways from various nanocatalysts and the uniqueness of each specific nanocatalyst.

Electrochemical treatment of domestic wastewater using boron-doped diamond and nanostructured amorphous carbon electrodes

The performance of the electrochemical oxidation process for efficient treatment of domestic wastewater loaded with organic matter was studied. The process was firstly evaluated in terms of its capability of producing an oxidant agent (H2O2) using amorphous carbon (or carbon felt) as cathode, whereas Ti/BDD electrode was used as anode. Relatively high concentrations of H2O2 (0.064 mM) was produced after 90 min of electrolysis time, at 4.0 A of current intensity and using amorphous carbon at the cathode. Factorial design and central composite design methodologies were successively used to define the optimal operating conditions to reach maximum removal of chemical oxygen demand (COD) and color. Current intensity and electrolysis time were found to influence the removal of COD and color. The contribution of current intensity on the removal of COD and color was around 59.1 and 58.8%, respectively, whereas the contribution of treatment time on the removal of COD and color was around 23.2 and 22.9%, respectively. The electrochemical treatment applied under 3.0 A of current intensity, during 120 min of electrolysis time and using Ti/BDD as anode, was found to be the optimal operating condition in terms of cost/effectiveness. Under these optimal conditions, the average removal rates of COD and color were 78.9 ± 2 and 85.5 ± 2 %, whereas 70% of total organic carbon removal was achieved.

Bioassay based luminescent bacteria: interferences, improvements, and applications

Due to the merits of being time-saving, cost effective and simple operation, the luminescent bacteria toxicity assay (LBTA) has been widely used for environmental pollution monitoring. Based on numerous studies since 2007, this critical review aims to give an overview on the mechanisms, developments and applications of LBTA. Firstly, based on the introduction of the mechanisms of LBTA, this review shows the interferences from the characteristics of testing samples (such as inorganic nutrients, color, turbidity) and summarizes the improvements on pretreatment method, test methods and test systems in recent years. Regarding the factors that affect the toxicity prediction of single chemicals, the correlation between the toxicity index expressed as median effective concentration (EC50) and characters (such as Kow, the alkyl chain length, the anion and the cation) of known chemicals, especially the emerging ionic liquids (ILs), were given an in-depth discussion. The models for predicting the joint effect of mixtures to luminescent bacteria were also presented. For the factors that affect the toxicity of actual waters, the correlation of toxicity of actual samples to luminescent bacteria and their conventional indexes were discussed. Comparing the sensitivity of the LBTA with other bioassays could indicate the feasibility of the LBTA applied on specific samples. The summary on the application of LBTA to environmental samples has been made to find the future research direction.

Electrochemical advanced oxidation processes: today and tomorrow. A review

In recent years, new advanced oxidation processes based on the electrochemical technology, the so-called electrochemical advanced oxidation processes (EAOPs), have been developed for the prevention and remediation of environmental pollution, especially focusing on water streams. These methods are based on the electrochemical generation of a very powerful oxidizing agent, such as the hydroxyl radical ((•)OH) in solution, which is then able to destroy organics up to their mineralization. EAOPs include heterogeneous processes like anodic oxidation and photoelectrocatalysis methods, in which (•)OH are generated at the anode surface either electrochemically or photochemically, and homogeneous processes like electro-Fenton, photoelectro-Fenton, and sonoelectrolysis, in which (•)OH are produced in the bulk solution. This paper presents a general overview of the application of EAOPs on the removal of aqueous organic pollutants, first reviewing the most recent works and then looking to the future. A global perspective on the fundamentals and experimental setups is offered, and laboratory-scale and pilot-scale experiments are examined and discussed.

Removal of chlortetracycline from spiked municipal wastewater using a photoelectrocatalytic process operated under sunlight irradiations

The degradation of chlortetracycline in synthetic solution and in municipal effluent was investigated using a photoelectrocatalytic oxidation process under visible irradiation. The N-doped TiO₂ used as photoanode with 3.4 at.% of nitrogen content was prepared by means of a radiofrequency magnetron sputtering (RF-MS) process. Under visible irradiation, higher photoelectrocatalytic removal efficiency of CTC was recorded using N-doped TiO₂ compared to the conventional electrochemical oxidation, direct photolysis and photocatalysis processes. The photoelectrocatalytic process operated at 0.6A of current intensity during 180 min of treatment time promotes the degradation of 99.1 ± 0.1% of CTC. Under these conditions, removal rates of 85.4 ± 3.6%, 87.4 ± 3.1% and 55.7 ± 2.9% of TOC, TN and NH₄(+) have been recorded. During the treatment, CTC was mainly transformed into CO₂ and H₂O. The process was also found to be effective in removing indicator of pathogens such as fecal coliform (log-inactivation was higher than 1.2 units).

Electrochemical degradation of chlortetracycline using N-doped Ti/TiO2 photoanode under sunlight irradiations

The appearance and the persistence of pharmaceutical products in the aquatic environment urgently call for the development of an innovative and practical water treatment technology. This study deals with the development of nanostructured nitrogen-doped TiO2 photoanodes and their subsequent use for chlortetracycline (CTC) photoelectrocatalytic oxidation under visible light. The N-doped TiO2 photoanodes with different nitrogen contents were prepared by means of a radiofrequency magnetron sputtering (RF-MS) process, with the objective to tune shift their optical absorption from the UV towards the visible. The N-doped TiO2 consist of nanostructured anatase phase with average TiO2 nanocrystallite size of 29 nm. The nitrogen doping is clearly shown to produce the desired red shift of the absorption onset of the TiO2 coatings (from ~380 nm to ~550 nm). Likewise, the N-doped TiO2 are found to be highly photo-electroactive not only under the UV light but most interestingly under the visible light as well. Using the optimal N-doped photoanodes, 99.6% of CTC (100 μg/L) was successfully degraded after 180 min of treatment time with a current intensity of 0.6 A. Under these conditions, a relatively high mineralization of CTC (92.5% ± 0.26% of TOC removal and 90.3% ± 1.1% of TN removal) was achieved.