Microwave Discharge Electrodeless Lamp Research Articles

Photocatalytic degradation of ammonia to nitrogen by anatase TiO2 under microwave discharge electrodeless lamp irradiation

In this study, a microwave discharge electrodeless lamp (MDEL) photo-degradation system coupled with anatase TiO2 (P25) was constructed to improve the selective degradation of NH3 to N2. The MDEL system can generate abundant reactive oxygen species (ROS) with ultraviolet radiation at 185 nm and 254 nm during gas phase reaction. The species and content of ROS generated in the reaction system were determined by oxidation extraction spectrophotometry, and the effects of residence time, temperature, and relative humidity on the production of reactive oxygen species were investigated. In addition, the removal efficiency under different conditions such as initial ammonia concentration, relative humidity and residence time was explored. It was found that the removal rate could reach 83% when the initial ammonia concentration was 100 ppm, relative humidity was 55% and gas residence time was 5.16 s. The high-energy ultraviolet at 185 nm from MDEL could break NH3 molecules in advance and produced a large amount of ·NH2. Besides, NH3 was converted to N2 by generating large amounts of ROS, reducing NOx and nitrate generation. Our work presents a novel approach to construct a photocatalytic system for high efficiency degradation of NH3.

Disinfection of wastewater by a complete equipment based on a novel ultraviolet light source of microwave discharge electrodeless lamp: Characteristics of bacteria inactivation, reactivation and full-scale studies

Ultraviolet (UV) light is widely used for wastewater disinfection. Traditional electrode-excited UV lamps, such as low-pressure mercy lamps (LPUV), encounter drawbacks like electrode aging and rapid light attenuation. A novel UV source of microwave discharge electrodeless lamp (MDEL) has aroused attention, yet its disinfection performance is unclear and still far from practical application. Here, we successfully developed a complete piece of equipment based on MDELs and achieved the application for disinfection in wastewater treatment plants (WWTPs). The light emitted by an MDEL (MWUV) shared a spectrum similar to that of LPUV, with the main emission wavelength at 254 nm. The inactivation rate of Gram-negative E. coli by MWUV reached 4.5 log at an intensity of 1.6 mW/cm2 and a dose of 20 mJ/cm2. For Gram-positive B. subtilis, an MWUV dose of 50 mJ/cm2 and a light intensity of 1.2 mW/cm2 reached an inactivation rate of 3.4 log. A higher MWUV intensity led to a better disinfection effect and a lower photoreactivation rate of E. coli. When inactivated by MWUV with an intensity of 1.2 mW/cm2 and a dose of 16 mJ/cm2, the maximum photoreactivation rate and reactivation rate constant Kmax of E. coli were 0.63 % and 0.11 % h−1 respectively. Compared with the photoreactivation, the dark repair of E. coli was insignificant. The full-scale application of the MDEL equipment was conducted in two WWTPs (10,000 m3/d and 15,000 m3/d). Generally 2–3 log inactivation rates of fecal coliforms in secondary effluent were achieved within 5–6 s contact time, and the disinfected effluent met the emission standard (1000 CFU/L). This study successfully applied MDEL for disinfection in WWTPs for the first time and demonstrated that MDEL has broad application prospects.

Efficient wastewater disinfection using a novel microwave discharge electrodeless ultraviolet system with ozone at an ultra-low dose

Microwave discharge electrodeless lamp (MDEL) is a novel ultraviolet (UV) light source. Synergistic disinfection using UV light emitted by MDEL (MWUV) coupled with ozone (O3) at an ultra-low dose was investigated. Escherichia coli and Bacillus subtilis were deactivated more effectively by MWUV/O3 than by either MWUV or O3 alone. MWUV/O3 treatment using an O3 concentration of 0.4 mg/L gave an E. coli inactivation rate of 5.52 log. The photoreactivation degree and rate of E. coli were lower after inactivation by MWUV/O3 treatment than after MWUV treatment alone. The maximum photoreactivation rates after the MWUV/O3 and MWUV treatments were 2.90% and 16.08%, respectively. MWUV/O3 disinfection also inhibited dark resurrection of E. coli and gave a maximum dark resurrection rate of 0.0036%. Electron paramagnetic resonance spectroscopy indicated that more hydroxyl radicals were generated during MWUV/O3 treatment. Scanning electron microscopy and laser confocal scanning microscopy observations indicated that O3 played a key role in breaking down the cell structure. MWUV/O3 treatment gave a good disinfection effect on fecal coliform bacteria in actual domestic wastewater. The results indicated that inactivation of bacteria can be more effectively achieved by MWUV treatment with O3.

마이크로파-이산화티타늄 광촉매 복합 시스템의 이부프로펜 분해 특성

Since pharmaceutical ingredients detected in the water environment have a harmful effect on humans and natural ecosystems, it is necessary to develop a treatment process that can properly remove them. In this study, the ibuprofen removal properties from aqueous solutions were investigated with a photocatalytic hybrid system based on microwaves, microwave discharge electrodeless lamps, and TiO₂ photocatalyst balls. In particular, the relationship between the microwave intensity, the initial concentration of ibuprofen, and the component technology of the photocatalytic hybrid system and the decomposition properties of ibuprofen were investigated. The amount of UV generated from MDEL, which is closely related to the degradation rate of ibuprofen, was affected by the microwave intensity. The optimal microwave intensity of the microwave-photocatalytic hybrid system used in this study was found to be 0.5 kW. Also, the degradation rate of ibuprofen decreased with increasing initial concentration. The TiO₂ photocatalyst system using microwave and MDEL showed the highest degradation constant value, which was related to the generation of reactive oxygen species. This study showed that the microwave-TiO₂ hybrid system process can be effectively applied to the removal of pharmaceutical-related contaminants.

Phase control and optimization of photocatalytical properties of samarium doped TiO2 synthesized by coupled ultraviolet and microwave radiations

The scientific community has been looking for strategies to synthesize active catalysts under Ultraviolet_Visible (UV_Vis) light to atrazine (ATZ) degradation. In this study, we applied for the first time the microwave (MW) energy and a Microwave Discharge Electrodeless Lamp (MDEL) as an UV_Vis light source to synthesize photocatalysts. The synergistic use of MW_UV_Vis energies allowed obtaining Sm-doped TiO2 with photoactivity under UV-A light (365 nm) to degrade ATZ. Different characterization analyzes showed that Sm3+ was inserted into the TiO2 lattice and prevented the conversion of anatase into rutile, in addition to giving rise to brookite phase, which increase under MDEL assisted synthesis. Different techniques proved the doping, and especially photoluminescence (PL) showed that electrons are excited to f levels of Sm3+ and can be trapped in the structural defects of the photocatalyst to be consumed later. Moreover, the catalyst synthesized under MDEL irradiation (STiM) showed lower recombination rates and a performance to degrade ATZ of 45% and 15% higher than pristine TiO2 (Ti) and Sm-doped TiO2 (STi), respectively. Photocatalytic degradation mechanism was unveiled by monitoring Desethyl-atrazine (DEAT), Desisopropyl-atrazine (DIAT), and Hydroxy-atrazine (HAT), which are by-products of ATZ. The doped materials showed high efficiency to activate the ATZ hydrolysis reaction, while the water oxidation to generate •OH and converted ATZ to HAT was more pronounced in STiM. We proved through radical probe tests that STiM produces more hydroxyl radicals and that its photoactivity remains even after 4 application cycles.

Combination of microwave discharge electrodeless lamp and a TiO2/HZSM-5 composite for the photocatalytic degradation of dimethyl sulphide

In this study, an integrated photocatalytic system consisting of a microwave discharge electrodeless lamp (MDEL) and TiO2/HZSM-5 was established to investigate the intensified degradation of dimethyl sulphide (DMS). The system targets optimisation of the reactive oxygen species (ROS) and photocatalytic degradation pathways without catalyst deactivation. TiO2/HZSM-5, containing highly dispersed TiO2 nanoparticles, was prepared through the sol-gel method. TiO2/HZSM-5 exhibits strong acidity and can adsorb DMS in multiple adsorption forms. Thus, the adsorption capacity of TiO2/HZSM-5 is 20 and 53 times higher than that of Aeroxide TiO2 (P25) in dry and highly humid air, respectively. UV–Vis analysis was performed to investigate the ROS in the gas phase. The results show that the concentrations of the ROS increased by 8% and 62.7% in dry and highly humid air, respectively. 1O2 and O (1D), as well as ·OH are the major ROS, accounting for 73.6% and 61.6% in dry and highly humid air, respectively. A total of 92.5% DMS was removed over 600 min in dry air. Microwaves have strong desorption effects on absorbed substances, promoting the degradation of DMS via ROS in the gas phase. Moreover, 1O2, O (1D), and ·OH can mineralise more DMS molecules into SO2 and SO3 through methanesulfonic acid. The highest mineralisation rate of 89.48% was obtained at 90% humidity over 600 min without catalyst deactivation. Therefore, this integrated system induced by microwave radiation can improve ROS production and prevent catalyst deactivation, providing an alternative to achieve higher photocatalytic performances in dry and highly humid air.

Enhanced photo-degradation of gaseous toluene over MnOx/TiO2/activated carbon under a novel microwave discharge electrodeless lamps system

Traditional photocatalytic oxidation of volatile organic compounds (VOCs) suffers low oxidation and mineralization capability, the short lifetime of the lamps, etc. The usage of microwave discharge electrodeless lamps (MDELs) is an energetic approach to eliminate pollutants with lamps having a long lifetime. Herein, a novel MDELs-photocatalytic system using MnOx/TiO2/activated carbon (AC) as the photocatalyst was explored to degrade toluene. The system displayed a superior toluene removal efficiency (94%) and mineralization rate (91%), and there was nearly no ozone emission. Owing to the formation of MnTiO3, the photocatalytic degradation activity over MnOx/TiO2/AC was remarkably increased by producing more reactive oxygen species, such as O(1D) and OH·. MnO and MnTiO3 in MnOx/TiO2/AC also promoted the decomposition of ozone to further degrade toluene via catalytic ozonation. Moreover, the excellent microwave absorbing property of MnOx/TiO2/AC increased the catalyst bed temperature to nearly 150 °C, accelerating the thermal decomposition of toluene due to the “hot spots” effect. The degradation mechanism was proposed tentatively. This work shed new light on the effective removal of VOCs using a novel MDELs photodegradation system over multi-functional catalysts.

Application of Microwave/Electrodeless Discharge Ultraviolet/Ozone Sterilization Technology in Water Reclamation

In recent years, a new water treatment technology based on microwave discharge electrodeless lamp (MDEL) has been developed. Hence, we designed an integrated system of microwave/electrodeless discharge ultraviolet/ozone (MW/UV/O3) for sewage sterilization according to the theoretical study of MDEL. The experiment was designed to test the ability to sterilize Escherichia coli and Bacillus subtilis by using different process conditions, such as single O3, MW/UV and MW/UV/O3, aiming to find an optimal process route. The results showed that the bactericidal effect of MW was mainly thermal effect, the bactericidal effect of MW/UV was significantly affected by turbidity, while the bactericidal effect of MW/UV/O3 was better than single O3 and MW/UV. In the dynamic test, when the four electrodeless UV lamps were stable, the light intensity reached 3.6mW/cm2; when the aeration rate was 50L/min, the generated O3 content was 0.30mg/L. With a water flow of 800L/h and hydraulic retention time of 1.5min, a sewage sterilization rate of >99.99% was achieved by MW/UV/O3 system, and other water quality indexes including chemical oxygen demand (COD) and total organic carbon (TOC) in effluents was also decreased to some extents.

Degradation behaviors of naproxen by a hybrid TiO2 photocatalyst system with process components

A hybrid system combining microwave and a microwave discharge electrodeless lamp (MDEL) was proposed to overcome the limitations of conventional TiO2 photocatalysts. The degradation efficiency and mechanism of naproxen were determined using a series of single processes, including conventional TiO2 photocatalyst reactors and a hybrid system that fuses them. Although the degradation efficiency tended to increase after changing the experimental condition of a single process, the optimal conditions existed for these experimental conditions. On the other hand, remarkable synergy was observed in the fused process, whose efficiency was significantly higher than that of the unit process. In particular, the optimal degradation ability was obtained by adding hydrogen peroxide together with microwave irradiation. The seven intermediates in the proposed photocatalytic degradation pathway were generated by the demethylation and hydroxylation by hydroxyl radicals. These results are expected to provide new data on the design of high efficiency photocatalytic systems at low cost.

Mineralization of cefoperazone in acid medium by the microwave discharge electrodeless lamp irradiated photoelectro-Fenton using a RuO2/Ti or boron-doped diamond anode.

The mineralization of 125 mL of 50-300 mg L-1 cefoperazone (CFPZ) has been comparatively studied by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation (AO), electro-Fenton (EF) and photoelectro-Fenton (PEF) with a RuO2/Ti or boron-doped diamond (BDD) anode and an activated carbon fiber (ACF) cathode. A microwave discharge electrodeless lamp (MDEL) was used as the UV source in PEF process. CFPZ decays always followed pseudo-first-order kinetics and their constant rates increased in the order: AO < EF < MDEL-PEF, regardless of anode types. Higher mineralization was achieved in all methods using BDD instead of RuO2/Ti, while the most potent BDD-MDEL-PEF gave 88% mineralization under its optimum conditions of 0.36 A, pH 3.0 and 1.0 mmol L-1 Fe2+. The synergistic mechanisms were explored by quantifying the electrogenerated H2O2 and formed •OH, in which 2.27 and 2.58 mmol L-1 H2O2 were accumulated in AO-H2O2 with RuO2/Ti or BDD anode, respectively, while 92.0 and 263.5 μmol L-1 •OH were generated in EF with RuO2/Ti or BDD anode, respectively. The oxidation power of EAOPs with different anodes was also compared by measuring the evolutions of NO3- and NH4+ as well as four generated carboxylic acids including oxalic, oxamic, formic and fumaric acids.

Degradation of methyl mercaptan by a microwave-induced photoreaction process

In this research, microwave discharge electrodeless lamp (MDEL) was applied to treat methyl mercaptan (MM). The influence factors of microwave-induced photoreaction on the malodor removal and MM degradation were intensively studied. The decline of malodor and MM concentration suggested that MDEL treatment has strong capability of deodorization and MM degradation. In addition, the irradiation of ultraviolet ray and visible light emitted from MDEL could remove over 99% of malodor at initial MM concentration of 90 ppmv in air atmosphere. The MM degradation analysis showed that MDEL played a significant role on the MM removal in N2, air and O2 atmosphere. Humidity had little effect on photo degradation in this system. However, the increment of initial MM concentration would decrease the degradation rate of MM, and total MM removal required longer time. Direct photolysis could remove a limited concentration of MM by MDEL in N2 atmosphere. When increasing O2 concentration and extending retention time, MM removal reached higher value. By comparing the results in N2 and air, it took shorter time to decompose MM completely in pure O2 atmosphere. This study provides a proof of concept that the combination of microwave and ultraviolet to deodorize MM, and the result can be used to optimize pilot-scale and full-scale experiment.

Microwave Discharge Electrodeless Lamps (MDELs). Part XI. Photolytic, Chemical Oxidation, and Photocatalytic Treatment of Aqueous Urea Solution with a Novel MDEL Photoreactor.

Decomposition of urea in aqueous solution was carried out using a microwave discharge electrodeless lamp (MDEL) consisting of two photoreactors with a triple tube structure that generate vacuum-UV/UV light and reactive oxygen species (ROS) using microwaves (MW) as an energy source. The rate of decomposition of urea was highest under acidic conditions (pH 4) compared with those at pH 7 and 10. When used in combination with dispersed TiO2, a photocatalyst, high decomposition efficiency was achieved with less power consumption. Moreover, decomposition efficiency more than two times higher than that of ozone oxidation and sodium hypochlorite oxidation could be realized.

Efficient mineralization of antibiotic ciprofloxacin in acid aqueous medium by a novel photoelectro-Fenton process using a microwave discharge electrodeless lamp irradiation

In this study, a novel photoelectro-Fenton (PEF) process using microwave discharge electrodeless lamp (MDEL) as a UV irradiation source was developed for the removal of antibiotic ciprofloxacin (CIP) in water. Comparative degradation of 200mgL−1 CIP was studied by direct MDEL photolysis, anodic oxidation (AO), AO in presence of electrogenerated H2O2 (AO-H2O2), AO-H2O2 under MDEL irradiation (MDEL-AO-H2O2), electro-Fenton (EF) and MDEL-PEF processes. Higher oxidation power was found in the sequence: MDEL photolysis < AO < AO-H2O2< MDEL-AO-H2O2< EF < MDEL-PEF. Effects of current density, pH, initial Fe2+ concentration and initial CIP concentration on TOC removal in MDEL-PEF process were examined, and the optimal conditions were ascertained. The releases of three inorganic ions (F−, NH4+ and NO3−) and two carboxylic acids (oxalic and formic acids) were qualified. Seven aromatic intermediates mainly generated from hydroxylation, dealkylation and defluorination of CIP were detected by UPLC-QTOF-MS/MS technology. Therefore, plausible degradation sequences for CIP degradation in MDEL-PEF process including all detected products were proposed.

Synthesis of TiO2–CTAB–SiC composite possessing the microwave absorption capacity and its photocatalytic performance in the microwave field

The synthesis of high activity TiO2–CTAB–SiC composite possessing the microwave absorption capacity has been reported. Herein, the commercial Silicon carbide (SiC) particles were used as the microwave absorbent and supporter. TiO2 nanopowders were loaded on the surface of SiC modified by hexadecyl trimethyl ammonium bromide (CTAB) via the hydrothermal route. The as-prepared TiO2–CTAB–SiC composite was characterized by X-ray diffraction, field-emission scanning electron microscopy, Fourier transformed infrared spectra, inductively coupled plasma-atomic emission spectrometry and fluorescence emission (PL). Its photocatalytic activity was evaluated by the degradation of rhodamine B in the microwave discharge electrodeless lamp (MDEL) system. The experimental results showed that TiO2–CTAB–SiC composite exhibited obviously higher photocatalytic activity in the MDEL system compared with pure TiO2 nanopowders. Their reusability and separation performance were evaluated by recycling experiments. The reasons for the improvement in photocatalytic performance were discussed in detail.

Photooxidation of Guaiacol to Organic Acids with Hydrogen Peroxide by Microwave Discharge Electrodeless Lamps

AbstractThe production of chemicals from lignin by green and sustainable technologies is a promising alternative route to replace fossil fuels. Photooxidation of guaiacol, a model of lignin, to value‐added carboxylic acids with microwave discharge electrodeless lamps as light source was investigated in the presence of hydrogen peroxide (H2O2). The coupled UV‐vis/microwave irradiation led to a more effective degradation of guaiacol than with conventional photocatalysis. Hydroxyl radicals as active species, confirmed by electron spin resonance spin‐trapping, were generated and participated in the oxidation. The effect of different operating conditions such as reaction time, guaiacol concentration, solution pH, as well as oxidant concentration, was evaluated.

Microwave discharge electrodeless lamps (MDELs). Part IX. A novel MDEL photoreactor for the photolytic and chemical oxidation treatment of contaminated wastewaters.

This article reports on the fabrication and enhanced performance of a novel microwave discharge electrodeless lamp (MDEL) consisting of a three layered cylindrical structure that was effective in the remediation of wastewater containing the 2,4-D herbicide and the near total sterilization of bacteria-contaminated pond water (E. coli and other microorganisms) through photolysis with the emitted vacuum-UV (185 nm) and UVC (254 nm) light from the MDEL and through chemical oxidation with reactive oxygen species (ROS) produced by the photolysis of dioxygen and air oxygen through one of the photoreactors. The flow rates of the 1.0 L contaminated waters were 0.6 and 1.2 L min(-1). The integrated UV/ROSO2 and UV/ROSair methods used to carry out the degradation of 2,4-D and sterilization processes were more effective than either the UV method alone or the ROSO2 and ROSair methods for short time periods (5 or 8 min). At a lower flow rate, 79% of 2,4-D was degraded by the UV/ROSO2 method and 55% by UV/ROSair after 8 min. At a faster flow rate of 1.2 L min(-1), degradation of 2,4-D in 1.0 L volume of water was 84% and 77% complete by the UV/ROSO2 and the UV/ROSair method, respectively, after 8 min of irradiation. The number of kills of E. coli bacteria was nearly quantitative (98 and 99%) by the UV/ROSO2 and UV/ROSair methods after treating the contaminated water for 5 min. The decrease of total viable microorganisms in pond water was 90% and 80% after 5 min of microwave irradiation at a flow rate of 1.2 L min(-1) by the integrated methods UV/ROSO2 and UV/ROSair, respectively. The rate of flow of oxygen gas through the photoreactor impacted the extent of degradation and the related dynamics of the 2,4-D herbicide.

Microwave Discharge Electrodeless Lamps. Part VIII: Continuous On‐Site Solar Energy Remediation of Contaminated Water

AbstractMicrowave discharge electrodeless lamps (MDELs) have been examined for continuous on‐site field treatment of contaminated water using solar cells to provide the necessary electrical power. The equipment aimed to decontaminate water in areas impacted by natural disasters such as the extensive earthquake that hit Eastern Japan in 2011. An energy‐saving semiconductor microwave generator provided the microwaves to activate the MDELs in a microwave/UV reactor setup operated using a single‐mode applicator and an E/H tuner. The herbicide 2,4‐dichlorophenoxyacetic acid degraded within a shorter time compared to methylene blue at a defined flow rate through the microwave/UV reactor. Sterilization of natural water contaminated with the bacterial microorganism Escherichia coli was complete within 20 min.

Photo-catalytic destruction of ethylene using microwave discharge electrodeless lamp

A double tube type microwave discharge electrodeless lamp was employed to investigate the photo-catalytic decomposition of ethylene gas, an important VOC species. The anatase TiO2 film photo-catalyst balls prepared by a low pressure metal organic chemical vapor deposition method were used. In addition, the advantages of microwave/UV/TiO2 photo-catalysts hybrid process were analyzed. The removal performance was examined under different conditions with different initial ethylene concentrations, gas residence times and oxygen concentrations. At all microwave powers tested, UV-C exhibited much larger irradiance than UV-A and UV-B. The degradation efficiency of ethylene increased with increasing microwave intensity, with decreasing inlet concentration, and with decreasing reaction gas flow rate. Taking the energy cost into account, residence time should be determined considering inlet concentration, volume of degradation, capacity of devices, and admitted costs. Microwave intensity was shown to be a critical operation variable for the photo-catalytic degradation of ethylene, required to be determined depending on initial ethylene concentration.

Removal of Refractory Organics from Biologically Treated Landfill Leachate by Microwave Discharge Electrodeless Lamp Assisted Fenton Process

Biologically treated leachate usually contains considerable amount of refractory organics and trace concentrations of xenobiotic pollutants. Removal of refractory organics from biologically treated landfill leachate by a novel microwave discharge electrodeless lamp (MDEL) assisted Fenton process was investigated in the present study in comparison to conventional Fenton and ultraviolet Fenton processes. Conventional Fenton and ultraviolet Fenton processes could substantially remove up to 70% of the refractory organics in a membrane bioreactor treated leachate. MDEL assisted Fenton process achieved excellent removal performance of the refractory components, and the effluent chemical oxygen demand concentration was lower than 100 mg L−1. Most organic matters were transformed into smaller compounds with molecular weights less than 1000 Da. Ten different polycyclic aromatic hydrocarbons were detected in the biologically treated leachate, most of which were effectively removed by MDEL-Fenton treatment. MDEL-Fenton process provides powerful capability in degradation of refractory and xenobiotic organic pollutants in landfill leachate and could be adopted as a single-stage polishing process for biologically treated landfill leachate to meet the stringent discharge limit.

Microwaves and their coupling to advanced oxidation processes: Enhanced performance in pollutants degradation

This review assesses microwaves (MW) coupled to advanced oxidation processes (AOPs) for pollutants degradation, as well as the basic theory and mechanisms of MW dielectric heating. We addressed the following couplings: MW/H2O2, MW/UV/H2O2, MW/Fenton, MW/US, and MW/UV/TiO2, as well as few studies that tested alternative oxidants and catalysts. Microwave Discharge Electrodeless Lamps (MDELs) are being extensively used with great advantages over ballasts. In their degradation studies, researchers generally employed domestic ovens with minor adaptations. Non-thermal effects and synergies between UV and MW radiation play an important role in the processes. Published papers so far report degradation enhancements between 30 and 1,300%. Unfortunately, how microwaves enhance pollutants is still obscure and real wastewaters scarcely studied. Based on the results surveyed in the literature, MW/AOPs are promising alternatives for treating/remediating environmental pollutants, whenever one considers high degradation yields, short reaction times, and small costs.