Direct Ultraviolet Photolysis Research Articles

Making waves: Opportunities and challenges of applying far-UVC radiation in controlling micropollutants in water.

Concerns over human health risks associated with chemical contaminants (micropollutants) in drinking waters are rising due to the increased use of reclaimed water or water supplies impacted by upstream wastewater discharges. Ultraviolet (UV)-driven advanced oxidation processes (UV-AOPs) using radiation sources that emit at 254nm have been developed as advanced treatments to degrade contaminants, while those UV-AOPs can be improved towards higher radical yields and lower byproduct formation. Several previous studies have suggested that Far-UVC radiation (200-230nm) is a promising radiance source to drive UV-AOPs because the direct photolysis of micropollutants and production of reactive species from oxidant precursors can both be improved. In this study, we summarize from the literature the photodecay rate constants of five micropollutants by direct UV photolysis, which are higher at 222 than 254nm. We experimentally determine the molar absorption coefficients at 222 and 254nm of eight oxidants commonly used in water treatment and present the quantum yields of the oxidant photodecay. Our experimental results also show that the concentrations of HO·, Cl·, and ClO· generated in the UV/chlorine AOP can be increased by 5.15-, 15.76-, and 2.86-fold, respectively, by switching the UV wavelength from 254 to 222nm. We also point out the challenges of applying Far-UVC for micropollutant abatement in water treatment, including the strong light screening effect of matrix components (e.g., carbonate, nitrate, bromide, and dissolved organic matter), the formation of byproducts via new reaction pathways, and the needs to improve the energy efficiency of the Far-UVC radiation sources.

Titania nano-coated quartz wool for the photocatalytic mineralisation of emerging organic contaminants.

Many emerging contaminants pass through conventional wastewater treatment plants, contaminating surface and drinking water. The implementation of advanced oxidation processes in existing plants for emerging contaminant remediation is one of the challenges for the enhancement of water quality in the industrialised countries. This paper reports on the production of a TiO2 nano-layer on quartz wool in a relevant amount, its characterisation by X-ray diffraction and scanning electron microscopy, and its use as a photocatalyst under ultraviolet radiation for the simultaneous mineralisation of five emerging organic contaminants (benzophenone-3, benzophenone-4, carbamazepine, diclofenac, and triton X-100) dissolved in deionised water and tap water. This treatment was compared with direct ultraviolet photolysis and with photocatalytic degradation on commercial TiO2 micropearls. The disappearance of every pollutant was measured by high performance liquid chromatography and mineralisation was assessed by the determination of total organic carbon. After 4 hours of treatment with the TiO2 nano-coated quartz wool, the mineralisation exceeds 90% in deionised water and is about 70% in tap water. This catalyst was reused for seven cycles without significant efficiency loss.

Photochemical decomposition of 1H,1H,2H,2H-perfluorooctane sulfonate (6:2FTS) induced by ferric ions

Perfluorooctane sulfonate (PFOS) had wide applications, such as in the electroplating industry, but its use was restricted in 2009 by the Stockholm Convention, due to its environmental persistence and potential hazards. As the most common PFOS alternative, 1H,1H,2H,2H-perfluorooctane sulfonic acid (6:2FTS) and its salts have been increasingly used. However, little is known about its photochemical decomposition. This paper reports the ferric ion-induced efficient decomposition and defluorination of 6:2FTS under 254nm ultraviolet (UV) irradiation; the underlying mechanisms were also investigated. In the presence of 100μmol/L ferric ion and at pH3.0, the first-order decomposition rate constant of 6:2FTS (10mg/L) was 1.59/hr, which was 6 times higher than for direct UV photolysis. The effects of the ferric ion concentration and the solution pH on the 6:2FTS photodecomposition were investigated and the optimal reaction conditions were determined. In addition to fluoride and sulfate ions, shorter-chain PFCAs (C2–C7) were detected as major intermediates. The addition of hydrogen peroxide or oxalic acid accelerated the decomposition of 6:2FTS under UV irradiation, but not its defluorination, indicating that hydroxyl radicals can directly react with 6:2FTS but not with the shorter-chain PFCAs. Accordingly, a mechanism for 6:2FTS photochemical decomposition in the presence of ferric ion was proposed, which comprises two reaction pathways. First, hydroxyl radicals can directly attack 6:2FTS, leading to CC bond cleavage. Alternatively, 6:2FTS coordinates with ferric ion to form Fe(III)-6:2FTS complexes, which can undergo ligand-to-metal charge transfer under UV irradiation, causing CS bond cleavage.

Removal of trace level amounts of twelve sulfonamides from drinking water by UV-activated peroxymonosulfate

Trace levels of residual antibiotics in drinking water may threaten public health and become a serious problem in modern society. In this work, we investigated the degradation of twelve sulfonamides (SAs) at environmentally relevant trace level concentrations by three different methods: ultraviolet (UV) photolysis, peroxymonosulfate (PMS) oxidation, and UV-activated PMS (UV/PMS). Sulfaguanidine, sulfadiazine, sulfamerazine, sulfamethazine, sulfathiazole, sulfamethoxydiazine, and sulfadimethoxine were be effectively removed by direct UV photolysis and PMS oxidation. However, sulfanilamide, sulfamethizole, sulfamethoxazole, sulfisoxazole, and sulfachloropyridazine were not completely degraded, despite prolonging the UV irradiation time to 30min or increasing the PMS concentration to 5.0mg·L−1. UV/PMS provided more thorough elimination of SAs, as demonstrated by the complete removal of 200ng·L−1 of all SAs within 5min at an initial PMS concentration of 1.0mg·L−1. UV/PMS promoted SA decomposition more efficiently than UV photolysis or PMS oxidation alone. Bicarbonate concentration and pH had a negligible effect on SA degradation by UV/PMS. However, humic acid retarded the process. Removal of 200ng·L−1 of each SA from a sample of sand-filtered effluent from a drinking water treatment plant (DWTPs) was quickly and completely achieved by UV/PMS. Meanwhile, about 41% of the total organic carbon (TOC) was eliminated. Scavenging experiments showed that sulfate radical (SO4−) was the predominant species involved in the degradation. It is concluded that UV/PMS is a rapid and efficient method for removing trace-level SAs from drinking water.

Toxicology Aspects of the Decomposition of Diuron by advanced Oxidation Processes

Abstract Diuron is a phenylurea-based residual herbicide with toxic and endocrine disrupting effects. The aims of the present work were the comparison of the efficiency of various advanced oxidation processes, such as direct ultraviolet photolysis, ozonation, their combination, and heterogeneous photocatalysis from the point of view of the transformation rate of diuron, rate of mineralisation and dehalogenation, formation of aromatic intermediates, and ecotoxicological effects of the formed multicomponent solutions during the treatments. The initial rates of transformation of diuron are in the order of ozonation < heterogeneous photocatalysis < UV photolysis < combination of UV photolysis and ozonation. Each method provided similar tendencies in the decrease of the concentration of organically bound chlorines (AOX) since, until the diuron was completely degraded, the concentration of AOX decreased almost to zero in each case. However, only heterogeneous photocatalysis was found to be effective in terms of mineralisation. Ecotoxicological results showed that in each case, except for ozonation, the toxicity of the treated solutions changed through a maximum during the transformation of diuron. The maximum value was found to be lower in the case of heterogeneous photocatalysis. Thus, the formation and decomposition of by-products of relatively higher toxicity than diuron can be supposed. Our results confirmed that the amount of the formed (aromatic) intermediates, their quality and specific toxicity strongly depend on the applied processes.

UV Photodegradation of Enoxacin in Water: Kinetics and Degradation Pathways

AbstractFluoroquinolones, such as enoxacin, are poorly removed by common sewage-treatment processes, leading to their discharge into the environment, where they have unknown, and potentially serious, impacts on plants and aquatic organisms. The aim of the research reported in this paper was to understand the degradation of enoxacin by direct UV (ultraviolet) photolysis and advanced oxidation processes (AOPs) involving UV/H2O2 and photo-Fenton [UV/H2O2/Fe(II)], which may provide an alternative method of removing this compound from water in a treatment plant. Aqueous samples of enoxacin (0.06 mM) were irradiated at 254 nm (Io=2×1016 photon s−1). The presence of H2O2, as well as the addition of FeSO4·7H2O (photo-Fenton process) both resulted in faster degradation kinetics compared to direct irradiation, with all of these systems leading to significant mineralization of enoxacin [>80% removal of total organic carbon (TOC)] within 30 min. The kinetics for the degradation of enoxacin in the presence of natural...

Photodegradation of emerging micropollutants using the medium-pressure UV/H2O2 Advanced Oxidation Process

A medium-pressure (MP) ultraviolet (UV) process has been applied to investigate the direct UV photolysis and UV/H2O2 oxidation of selected model micropollutants (naproxen, carbamazepine, diclofenac, gemfibrozil, ibuprofen, caffeine, 2,4-D, 2,4-DCP, and mecoprop). The quantum yields were found to be between0.0010and 0.13 at pH = 7. In the MP UV/H2O2 oxidation, the pseudo first-order rate constants for the selected compounds were found to be dependent on their initial concentrations (at mg/L levels) and on the H2O2 concentration. The UV doses required for 50% and 90% removal at various H2O2 levels varied widely among the compounds tested. Second-order rate constants (ranging from 4.1 × 109 to 1.4 × 1010 M−1 s−1) for the reaction between the selected compounds and hydroxyl radicals were determined using a competition-kinetics approach, where para-chlorobenzoic acid (pCBA) was chosen as the reference compound. Further, as an evaluation of electrical energy efficiency, the Figure-of-Merit, Electrical Energy per Order (EEO) was determined for the selected compounds using a batch reactor at 25 and 50 mg/L H2O2 concentrations. The electrical energy (in kWh) required to reduce a pollutant concentration by 90% ranged from 1.3 to 7.1 kWh m−3.

Degradation of selected pharmaceuticals in aqueous solution with UV and UV/H 2O 2

The degradation of four pharmaceutical compounds (PhACs), ibuprofen (IBU), diphenhydramine (DP), phenazone (PZ), and phenytoin (PHT) was investigated via ultraviolet (UV) photolysis and UV/H 2O 2 process with a low-pressure (LP) UV lamp. For each PhAC tested, direct photolysis quantum yields at 254 nm were found to be ranging from 6.32 × 10 −2 to 2.79 × 10 −1 mol E −1 at pH 7. The second-order rate constants of the reaction between the PhACs and OH were determined to be from 4.86 × 10 9 to 6.67 × 10 9 M −1 s −1 by using a competition kinetic model which utilized para-chlorobenzoic acid ( pCBA) as a reference compound. The overall effect of OH radical scavenging from humic acid (HA) and anions HCO 3 −, NO 3 − was measured utilizing R OH,UV method through examining the aqueous photodegradation of pCBA as a probe compound. Moreover, these fundamental direct and indirect photolysis parameters were applied in the model prediction for oxidation rate constants of the PhACs in UV/H 2O 2 process. It was found that the predicted oxidation rate constants approximated the observed ones. The results indicated that the new R OH,UV probe compound method was applicable for measuring background OH radical scavenging effects in water treatment process of UV/H 2O 2. Furthermore, by GC–MS analysis, most of the intermediates created during the photodegradation of the selected PhACs in UV/H 2O 2 process were identified. For the photodegradation of PZ, a competition mechanism existed between the direct UV photolysis and the oxidation of OH. An appropriate dosage of H 2O 2 could hinder the occurrence of the direct photolysis.

Japan striving for international standards for visible-light photocatalysts

Trace levels of residual antibiotics in drinking water may threaten public health and become a serious problem in modern society. In this work, we investigated the degradation of twelve sulfonamides (SAs) at environmentally relevant trace level concentrations by three different methods: ultraviolet (UV) photolysis, peroxymonosulfate (PMS) oxidation, and UV-activated PMS (UV/PMS). Sulfaguanidine, sulfadiazine, sulfamerazine, sulfamethazine, sulfathiazole, sulfamethoxydiazine, and sulfadimethoxine were be effectively removed by direct UV photolysis and PMS oxidation. However, sulfanilamide, sulfamethizole, sulfamethoxazole, sulfisoxazole, and sulfachloropyridazine were not completely degraded, despite prolonging the UV irradiation time to 30 min or increasing the PMS concentration to 5.0 mg·L− 1. UV/PMS provided more thorough elimination of SAs, as demonstrated by the complete removal of 200 ng·L− 1 of all SAs within 5 min at an initial PMS concentration of 1.0 mg·L− 1. UV/PMS promoted SA decomposition more efficiently than UV photolysis or PMS oxidation alone. Bicarbonate concentration and pH had a negligible effect on SA degradation by UV/PMS. However, humic acid retarded the process. Removal of 200 ng·L− 1 of each SA from a sample of sand-filtered effluent from a drinking water treatment plant (DWTPs) was quickly and completely achieved by UV/PMS. Meanwhile, about 41% of the total organic carbon (TOC) was eliminated. Scavenging experiments showed that sulfate radical (SO4−) was the predominant species involved in the degradation. It is concluded that UV/PMS is a rapid and efficient method for removing trace-level SAs from drinking water.

Photodegradation of Metolachlor Applying UV and UV/H2O2

Metolachlor is one of the most widely used herbicides in the world for controlling weeds. It has been detected in both ground and surface waters in the United States, and there are rising concerns in regard to its health risks and in developing effective treatment processes for its removal from water. Degradation of metolachlor via ultraviolet (UV) photolysis and an UV/hydrogen peroxide advanced oxidation process (AOP) was studied. The quantum yield of metolachlor at 254 nm was found to be 0.302 +/- 0.001 mol E-1 through direct UV photolysis in the range of pH 6-8. The second-order rate constant of the reaction between metolachlor and hydroxyl radical was determined to be 9.07 (+/-0.21) x 10(9) M-1 s-1 by using a competition kinetics model that utilized nitrobenzene as a reference compound. In addition, these parameters were successfully applied in modeling the kinetics of elimination of metolachlor using an UV/H2O2 process in both laboratory and natural waters. The formation of several photolysis byproducts was identified using gas chromatography/mass spectrometry, and a scheme for the metolachlor photodegradation pathway is proposed.

Inactivation of E. coli, B. subtilis spores, and MS2, T4, and T7 phage using UV/H 2O 2 advanced oxidation

The goal of this study was to evaluate the potential of an advanced oxidation process (AOP) for microbiocidal and virucidal inactivation. The viruses chosen for this study were bacteriophage MS2, T4, and T7. In addition, Bacillus subtilis spores and Escherichia coli were studied. By using H 2O 2 in the presence of filtered ultraviolet (UV) irradiation (UV/H 2O 2) to generate wavelengths above 295 nm, the direct UV photolysis disinfection mechanism was minimized, while disinfection by H 2O 2 was also negligible. Virus T4 and E. coli in phosphate buffered saline (PBS) were sensitive to >295 nm filtered UV irradiation (without H 2O 2), while MS2 was very resistant. Addition of H 2O 2 at 25 mg/l in the presence of filtered UV irradiation over a 15 min reaction time did not result in any additional disinfection of virus T4, while an additional one log inactivation for T7 and 2.5 logs for MS2 were obtained. With E. coli, only a slight additional effect was observed when H 2O 2 was added. B. subtilis spores did not show any inactivation at any of the conditions used in this study. The OH radical exposure (CT value) was calculated to present the relationship between the hydroxyl radical dose and microbial inactivation.

UV and UV/H2O2 treatment of methylisoborneol (MIB) and geosmin in water

The presence of taste and odour-causing compounds in water can lead consumers to perceive the water as unsafe and thus is a great concern for water utilities. This study examined the effectiveness of direct ultraviolet (UV) photolysis and the UV/hydrogen peroxide (H 2 O 2 ) advanced oxidation process (AOP) for removing methylisoborneol (MIB) and geosmin from raw source water and treated water. Low Pressure (LP) and Medium Pressure (MP) direct UV photolysis removed 10% and 25–50% of the compounds by 1000 mJ cm −2 UV fluence, respectively. The addition of H 2 O 2 created advanced oxidation conditions, and oxidized greater than 70% of these compounds at a UV fluence of 1000 mJ cm −2 . MP UV + H 2 O 2 was consistently faster than LP UV + H 2 O 2 for MIB oxidation, but water quality affected both of the UV + H 2 O 2 AOPs. The UV + H 2 O 2 AOP oxidation of these taste and odour contaminants in natural waters was effectively modelled using the steady state OH radical concentration model. Finally, electrical energy per order (E EO ) values for oxidation of MIB and geosmin were determined for a model UV reactor, and indicated that the UV + H 2 O 2 AOP requires less than 5 kWh of UV energy to oxidize 90% of MIB or geosmin in 1,000 gallons (3,785 liters) of clearwell or raw blend water, corresponding to a cost of less than US$0.35 per 1000 US gallons (3,785 liters).

Degradation of Endocrine Disrupting Chemicals Bisphenol A, Ethinyl Estradiol, and Estradiol during UV Photolysis and Advanced Oxidation Processes

The degradation of three endocrine disrupting chemicals (EDCs), bisphenol A, ethinyl estradiol, and estradiol, was investigated via ultraviolet (UV) radiation photolysis and the UV/hydrogen peroxide advanced oxidation process (AOP). These EDCs have been detected at low levels in wastewaters and surface waters in both the United States and European countries, can cause adverse effects on humans and wildlife via interactions with the endocrine system, and thus must be treated before entering the public drinking water supply. Because many EDCs can only be partially removed with conventional water treatment systems, there is a need to evaluate alternative treatment processes. For each EDC tested, direct UV photolysis quantum yields were derived for use with both monochromatic low-pressure (LP) UV lamps and polychromatic medium-pressure (MP) UV lamps and second-order hydroxyl radical rate constants were developed. These parameters were utilized to successfully model UV treatment of the EDCs in laboratory and natural waters. The polychromatic MP UV radiation source was more effective for direct photolysis degradation as compared to conventional LP UV lamps emitting monochromatic UV 254 nm radiation. However, in all cases the EDCs were more effectively degraded utilizing UV/H2O2 advanced oxidation as compared to direct UV photolysis treatment.