Low-pressure Mercury UV Lamp Research Articles

Enhanced Direct Photolysis of Organic Micropollutants by Far-UVC Light at 222 nm from KrCl* Excilamps.

Krypton chloride (KrCl*) excilamps emitting at far-UVC 222 nm represent a promising technology for microbial disinfection and advanced oxidation of organic micropollutants (OMPs) in water treatment. However, direct photolysis rates and photochemical properties at 222 nm are largely unknown for common OMPs. In this study, we evaluated photolysis for 46 OMPs by a KrCl* excilamp and compared it with a low-pressure mercury UV lamp. Generally, OMP photolysis was greatly enhanced at 222 nm with fluence rate-normalized rate constants of 0.2-21.6 cm2·μEinstein-1, regardless of whether they feature higher or lower absorbance at 222 nm than at 254 nm. The photolysis rate constants and quantum yields were 10-100 and 1.1-47 times higher, respectively, than those at 254 nm for most OMPs. The enhanced photolysis at 222 nm was mainly caused by strong light absorbance for non-nitrogenous, aniline-like, and triazine OMPs, while notably higher quantum yield (4-47 times of that at 254 nm) occurred for nitrogenous OMPs. At 222 nm, humic acid can inhibit OMP photolysis by light screening and potentially by quenching intermediates, while nitrate/nitrite may contribute more than others to screen light. Overall, KrCl* excilamps are promising in achieving effective OMP photolysis and merit further research.

Inactivation of foodborne pathogenic bacteria in water and stainless steel surfaces by vacuum-UV amalgam lamp and low-pressure mercury UV lamp irradiation

The objective of this study was to investigate the inactivation mechanism of a vacuum-ultraviolet (VUV)-amalgam lamp and its bactericidal efficacy on a stainless-steel surface and water compared with that of a conventional low-pressure mercury ultraviolet (LP) lamp. When treated with the VUV-amalgam and LP lamp over distilled water, initial 6–7 log CFU/mL of the foodborne pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes) were inactivated over 4.5 log after 60 mJ/cm2 treatment. However, there was no significant difference (p > 0.05) from the action of the VUV-amalgam lamp and conventional LP lamp at the same dose. However, on the stainless steel surface, the VUV-amalgam lamp treatment showed over 1.5 log higher inactivation capacity against the three pathogens at the same 254 nm dose irradiation of the LP lamp. Results of this study suggested that the VUV-amalgam lamp can be applied as a potential substitute for a conventional LP lamp for surface disinfection and limited water disinfection if ozone generation is well controlled.

Photooxidation of atrazine and its influence on disinfection byproducts formation during post-chlorination: effect of solution pH and mechanism

Partial photooxidation of micropollutants may lead to various degradation intermediates, obviously affecting disinfection byproducts (DBPs) formation during the post-chlorination process. The photooxidation of atrazine (ATZ) in aqueous solutions with low-pressure mercury UV lamps in UV, UV/H2O2 and UV/TiO2 treatment system and the formation of chlorinated disinfection byproducts (DBPs) during subsequent chlorination processes including dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), 1,1,1-trichloro-2-propanone (TCP), trichloromethane (TCM) and chloropicrin (CHP) were investigated in this study. The effect of solution pH on the oxidation pathway of ATZ in three UV photooxidation treatment process and the impact of photooxidation on the DBPs formations were assessed. Based on UPLC-ESI–MS/MS analyses, identification of main oxidation intermediates was performed and the plausible degradation pathways of ATZ in photooxidation system were proposed, indicating that photooxidation of ATZ in UV/H2O2 and UV/TiO2 process system was significantly pH-dependent processes. Dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), 1,1,1-trichloro-2-propanone (TCP), trichloromethane (TCM) and chloropicrin (CHP) were detected in photooxidized ATZ solutions. Compared to the other three DBPs, TCM and TCP were the main DBPs formed. The DBPs formations were greatly promoted in oxidized ATZ solutions. Solution pH and UV irradiation time exhibited obvious impact on the DBPs formation on the basis of DBP species. The variation tendency of DBPs observed relates to the combustion of ATZ in photooxidation system and the production oxidation intermediates.

Comparison of Chemistry Induced by Direct and Indirect Plasma Treatment of Water to the Effect of UV Radiation

The yield of redox reactions (Fe2+ oxidation and Mn7+ reduction in aqueous solutions) under the action of hot plasma radiation in liquid and species formed in the region of plasma discharge was measured. The goal of the investigation is to evaluate the role of hot plasma radiation as active factor compared to species generating in discharge itself. As source of active species we studied the spark discharge in air and in nitrogen (SD50 generator), the generator of corona discharge in air and low-pressure mercury UV lamp (λ = 253.7 nm). The yield of redox reactions for all sources was determined using detecting liquids; the mechanisms of these reactions were analysed. It was shown that chain reactions do not take place. When the yields were calculated, the stoichiometry of the reactions was taken into account. An analysis of the results shows that under the action of a spark discharge generator SD50, the main active factor is radiation. The role of active species formed in discharge region not more than 15%. Under the action of a spark discharge radiation, active species first form in the sample being processed, and then interact with substances dissolved in water. There is an indirect mechanism of action. Owing of this peculiarity, the redox properties of water, activated by hot plasma radiation, are the same as direct treatment of samples to hot plasma radiation. For a corona discharge plasma and radiation from a mercury lamp, such a mechanism does not occur.

Investigation of a new UVC LEDs array continuous type water disinfection system for inactivating Escherichia coli O157:H7 according to flow rate and electrical energy efficiency analysis

UVC LEDs are gaining popularity for its advantages which compensate for the limitations of low-pressure mercury UV lamps. In order to investigate the efficacy of UVC LEDs-based continuous water disinfection system, various numbers of UVC LEDs chips were introduced to inactivate Escherichia coli O157:H7 in water. Also, the effect of an aluminum reflector in the irradiation system was investigated in order to enhance bacterial inactivation. Without the reflector, the pathogen inactivation profile showed a sigmoidal curve, while linear fitting was shown for the treatment with the reflector, and there was a 1.5 times greater bactericidal effect when the reflector was installed. Based on the inactivation rate constant, no significant differences were revealed among the UVC LEDs chip arrays. Electrical energy efficiency necessary for 3- and 5-log reductions were calculated and the 18 UVC LEDs chip array consumed 30% less energy compared to the 33 UVC LEDs array. In this study, kinetic profiles of E. coli O157:H7 in a continuous water disinfection system using UVC LEDs irradiation with or without a reflector under various operational currents were obtained. Electrical energy consumption was considered in order to optimize the efficacy of this disinfection system. These results can be used as practical database to develop a water disinfection system using UVC LEDs and attributed to water and food safety.

The impact of wastewater matrix on the degradation of pharmaceutically active compounds by oxidation processes including ultraviolet radiation and sulfate radicals.

Ultraviolet radiation (UV)-activated peroxydisulfate (PDS) and peroxymonosulfate (PMS) advanced oxidation processes were examined for their capacity to remove nine pharmaceutically active compounds (PhACs) from secondary effluent. The effect of operational parameters (initial oxidant concentration, UV exposure time, pH, common coexisting anions and effluent organic matter (EfOM)) on UV/PDS and UV/PMS treatment efficiency was investigated in a collimated beam device housing a low-pressure mercury UV lamp emitting light at 253.7 nm. Both AOPs achieved high removals (>90%) when applied to pure water. Under otherwise similar conditions the removal percentage fell by 20-30% due to the scavenging of effluent organic matter (EfOM) in secondary effluent. Finally, eliminating EfOM but maintaining the inorganic composition, the radical scavenging effect was reduced and 98.3% and 85.6% average removals were obtained by UV/PDS and UV/PMS, respectively. Increasing pH improved degradation of several PhACs containing amine groups. Higher oxidant dosages created only a significant benefit in UV/PDS. The chloride anion produced a negligible effect on both processes, while higher nitrate concentrations increased removal percentage but did not affect degradation rate constants. Finally and surprisingly, the addition of bicarbonate had the strongest positive impact on the degradation kinetics observed, even stronger than the elimination of EfOM from secondary effluent.

Identification of intermediates, acute toxicity removal, and kinetics investigation to the Ametryn treatment by direct photolysis (UV254), UV254/H2O2, Fenton, and photo-Fenton processes.

This paper reports the degradation of 10mgL-1 Ametryn solution with different advanced oxidation processes and by ultraviolet (UV254) irradiation alone with the main objective of reducing acute toxicity and increase biodegradability. The investigated factors included Fe2+ and H2O2 concentrations. The effectiveness of the UV254 and UV254/H2O2 processes were investigated using a low-pressure mercury UV lamp (254nm). Photo-Fenton process was explored using a blacklight blue lamp (BLB, λ = 365nm). The UV254 irradiation process achieved complete degradation of Ametryn solution after 60min. The degradation time of Ametryn was greatly improved by the addition of H2O2. It is worth pointing out that a high rate of Ametryn removal was attained even at low concentrations of H2O2. The kinetic constant of the reaction between Ametryn and HO● for UV254/H2O2 was 3.53 × 108Lmol-1s-1. The complete Ametryn degradation by the Fenton and photo-Fenton processes was observed following 10min of reaction for various combinations of Fe2+ and H2O2 under investigation. Working with the highest concentration (150mgL-1 H2O2 and 10mgL-1 Fe2+), around 30 and 70% of TOC removal were reached within 120min of treatment by Fenton and photo-Fenton processes, respectively. Although it did not obtain complete mineralization, the intermediates formed in the degradation processes were hydroxylated and did not promote acute toxicity of Vibrio fischeri. Furthermore, a substantial improvement of biodegradability was obtained for all studied processes.

Impact of natural organic matter on bromate removal in the sulfite/UV-L advanced reduction process

Advanced reduction processes (ARPs) are treatment processes that involve combining reducing reagents and activating tools to produce highly reactive reducing free radicals. The process has proven effective for treating oxidized contaminants, and the effects of process variables on the degradation kinetics of various target contaminants have been investigated in our previous studies. In natural environments, natural organic matter (NOM) is found in surface or ground water. NOM absorbs UV light and can react with photochemically produced radicals, thus affecting target contaminant photochemical reactions and further influencing the efficiency of ARP. This study examines the impact of humic acid (HA) and Suwanee River NOM on bromate reduction rates with UV irradiation using a low-pressure mercury UV lamp. The effects of the sulfite dose, solution pH, and light intensity are studied and the pseudo-first-order rate constants in the presence of HA (kobs,HA) are compared to those observed in the absence of HA (kobs). At low HA concentrations of 1 mg L−1, kobs,HA was larger than kobs; however, kobs,HA was less than kobs at higher HA concentrations. Furthermore, kobs,HA did not increase with increasing sulfite doses in the presence of HA, which is unlike the behavior of kobs.

Aniline degradation in aqueous solution by UV-aeration and UV-microO3 processes: Efficiency, contribution of radicals and byproducts

The use of combination of air and UV irradiation for organic matters removal has drawn attention since degradation efficiency would be significantly enhanced in the presence of oxygen. Considering the fact that a low-pressure mercury UV lamp (emitting at 254nm and 185nm) could dissociate oxygen in gas phase and generate ozone, UV irradiation with addition of ozone enriched air, generated by the same UV lamp, was introduced. This technology was called UV-microO3 because the concentration of ozone generated by UV irradiation was relatively low (lower than 1mgL−1). The degradation of aniline by UV-aeration and UV-microO3 processes was comparatively analyzed. It was shown that aniline underwent much faster and more complete degradation in UV-microO3 process than in UV-aeration system. Hydroxyl radical (OH) exposure in UV-microO3 process was 2.46times of that in UV-aeration system. Furthermore, increasing inlet air flow rate would be of benefit to maintaining high dissolved oxygen (DO) level in UV-aeration system, thus the aniline removal was improved. While concentration of ozone generated by UV irradiation increased at first and then declined as the air flow rate increased from 1.8Lmin−1 to 4.8Lmin−1 in UV-microO3 process, and similar trend for aniline removal rate was observed. The contributions of radicals on aniline removal in UV-aeration and UV-microO3 processes were calculated to be 23.1% and 67.7%. The formation of 4-aminophenol, 4-Hydroxydiphenylamine, azobenzene and 4-Phenylazophenol was observed as the major intermediates in UV-aeration and UV-microO3 processes, mechanism of aniline degradation was proposed based on experimental evidence.

An experimental and modelling investigation of the effect of the flow regime on the photocatalytic degradation of methylene blue on a thin film coated ultraviolet irradiated spinning disc reactor

AbstractIn this work, the impact of wave regime and operational parameters on the photocatalytic degradation of methylene blue was investigated on a thin film coated ultra-violet spinning disc. In the employed experimental setup, the wave regimes of spiral, unstructured and crisscross waves as well as smooth film could be observed at disc rotational speeds of 50–200rpm and flow rates of 5–20mL/s with a calculated average thickness of 160–450μm. The glass discs were coated with anatase TiO2 by a sol–gel procedure followed by heat treatment at 500° C for 1h. The reactor was irradiated by a low pressure mercury UV lamp producing an irradiance of 12–23W/m2 on the disc surface. The reactant was saturated with oxygen and the effect of spinning speed, flow rate and the resulting wave regime on the degradation rate and kinetics of methylene blue and its reaction intermediates determined. Reactions followed pseudo-second-order kinetics, suggesting dimerisation and/or mass transfer limitations given that the two reactions with the highest conversion observed at 15mL/s and 100 and 200rpm, were pseudo-first-order. The spinning disc reactor was, however, not photon transfer limited. The wave regimes showed no impact on the reaction rate, since the flow was mainly laminar with no interfacial mass transfer of oxidant required.

A finite model for the prediction of the UV radiation field around a linear lamp

A finite model was established to predict the radiation field around a line lamp treating contaminated air, taking into account the effects of the radius of the lamp and sleeve, as well as other physical parameters. Both irradiance and fluence rate could be calculated, and the model was validated with measured data and by comparison with a conventional extense source volumetric emission (ESVE) model. Diffuse and specular emissions for a line lamp were compared, showing that diffuse emission is more appropriate for a low pressure mercury UV lamp. Refraction by the lamp sleeve can induce a 12% increase in fluence rate near the sleeve, while reflection causes a 7% decrease. When the attenuation coefficient of a gaseous chemical is less than 0.04 m −1 the error due to ignoring its light absorption is less than 1%, within a distance of 0.2 m from the lamp.

Continuous surface modification process with ultraviolet/ozone for improving interfacial adhesion of poly(ethylene terephthalate)/epoxy composites

This study proposed a continuous UV/ozone surface modification process for the production of polymeric fiber-reinforced polymer composite. A gas phase photoreactor using the conventional low-pressure mercury UV lamps and the economically made ozone generators were designed and constructed. Poly(ethylene terephthalate) (PET) fibers and epoxy resin were chosen as a reinforcement and a matrix, respectively. The synergistic effects of UV and various gas species (nitrogen, air, oxygen, air/ozone, and oxygen/ozone) exposure as well as the effects of exposure time, i.e., 2, 5, and 10 min, on the morphology and chemistry of PET-fiber surfaces were investigated by using a scanning electron microscope coupled with energy dispersive x-ray analysis (SEM/EDX). The tensile testing and analysis of fractography of the resulted composites were performed to evaluate the effectiveness of the process. The SEM/EDX results showed that the effects of the treatment were dependent on both the concentration of reactive species present in the gases and the exposure time. The PET fibers treated under UV/O2 + O3 exposure for 5 min yielded the resulting composite with the highest tensile strength value. Under this condition, the tensile strength of the composite can be increased up to 63% in comparison with that of the untreated PET fiber/epoxy composite. The results are of interest for application as an in-line surface modification for composite productions. POLYM. COMPOS., 27:484–490, 2006. © 2006 Society of Plastics Engineers

Removal of dimethyl phthalate from water by UV–H2O2 process

This study aims to demonstrate the removal efficiency of dimethyl phthalate from water using the UV–H2O2 photooxidation process. Pure water samples, spiked with 20 ppm dimethyl phthalate (DMP) were treated by the combined effect of UV photolysis as well as hydrogen peroxide oxidation mechanisms. In the experiments, the concentration of hydrogen peroxide was varied from 34 to 136 ppm and a low-pressure mercury UV lamp of 100 mW power output was used to provide the necessary radiation. The effects of initial concentration of H2O2, UV exposure time, pH, and temperature were investigated. The results showed that about 60% of DMP were removed directly by activation caused by UV light radiation intensity after an exposure time of 1 h. However, the removal efficiency increased when the DMP-spiked water was dosed with H2O2 prior to irradiating with UV light (i.e., UV–H2O2). More than 98% of DMP was removed after 45 min when the UV-irradiated solution was dosed with 136 ppm of H2O2. The results also showed that lowering the pH and increasing the temperature enhanced the removal of DMP by UV–H2O2 process. Key words: ultraviolet light, hydrogen peroxide, hydroxyl radical, phthalates, UV–H2O2 process, advanced oxidation processes.

Kinetics and mechanisms of UV-photodegradation of chlorinated organics in the gas phase

Over the last two decades, the application of photodegradation for the destruction of a wide spectrum of organic compounds in air has gained considerable interest in abating environmental pollution. This paper presents the results of a fundamental study conducted to evaluate the gas phase oxidation kinetics of volatile organic compounds (VOCs) with respect to different parameters pertinent to the operating conditions of air stripping and soil vapor extraction processes. Photodegradations of three chlorinated VOCs: chloroform, carbon tetrachloride (CTC) and trichloroethylene (TCE), were investigated in a semi-batch reactor using a low-pressure mercury UV lamp. The effects of different experimental parameters, such as the initial concentrations of the VOCs, the reaction medium, relative humidity, light intensity, temperature and the effect of mixture that may influence the kinetics of the gas phase photodegradation were evaluated. Mechanisms of photodegradation as supported by the experimental data are also proposed.

Application of ultraviolet photooxidation to remove organic pollutants in the gas phase

Abstract The photooxidation of volatile organic compounds (VOCs) such as benzene, toluene, and cis- 1, 2-dichloroethylene (DCE) using low-pressure mercury UV lamp as the irradiation source is described. The kinetics of the gas phase photooxidation was evaluated by varying different conditions, such as initial concentrations of the VOCs, intensity of radiation, humidity, temperature and reaction medium. The results showed that the low-pressure mercury UV lamp with relatively low radiant intensity is capable of destroying various types of organic pollutants. The photooxidation rates increased with the presence of moisture and the chloride radical in the mixture, and the effect was more pronounced for compounds with reactive hydrogen. The results indicate that the photooxidation process is ideal for on-site non-combustion destruction of different types of organics present in the off-gas resulting from treatment technologies such as soil-vapor extraction and air stripping.

Development of rubbery materials with excellent barrier properties to H 2, D 2, and T 2

Various acrylonitrile-butadiene copolymers, known as NBR, are known to have much lower gas permeabilities than other rubbers. The purpose of this study is to prepare chemically modified NBR membranes having even lower tritium permeability than unmodified NBR, combined with good antiradiation properties. NBR 41, an acrylonitrile-butadiene copolymer in which the content of acrylonitrile is 41 mol%, was used. Bromination of the NBR 41, to give Br-NBR-41, was carried out by immersing an NBR 41 membrane in saturated bromine water at 20°C and irradiating with a low pressure mercury UV lamp. Membranes of a polymer blend of NBR 41 with poly(vinyl chloride)- N,N-dimethyldithiocarbamate, or PDM, known as Blend-NBR-41, were prepared. PDM was synthesized by the reaction of poly(vinyl chloride) with sodium N,N-dimethyldithiocarbamate. The bromination of Blend-NBR-41, to give Br-Blend-NBR-41, was carried out by the technique used for preparation of the Br-NBR-41 membranes. Temperature dependence of the apparent permeability of NBR-41, Blend-NBR-41 and Br-Blend-NBR-41 to H 2, D 2 and He was studied. These modified NBR membranes showed excellent barrier properties for H 2, D 2 and He over a wide range of temperatures. The permeability of T 2 through the Br-Blend-NBR-41 membrane at room temperature was about 6% lower than that of H 2. The gas evolution from NBR-41 on gamma-ray irradiation was compared with that from the modified NBR-41. The small amount of gaseous products from the modified NBR-41 suggests that this material has excellent antiradiation properties.