An inexpensive UV-LED photoacoustic based real-time sensor-system detecting exhaled trace-acetone

In this research we present a low-cost system for breath acetone analysis based on UV-LED photoacoustic spectroscopy. We considered the end-tidal phase of exhalation, which represents the systemic concentrations of volatile organic compounds (VOCs) - providing clinically relevant information about the human health. This is achieved via the development of a CO2-triggered breath sampling system, which collected alveolar breath over several minutes in sterile and inert containers. A real-time mass spectrometer is coupled to serve as a reference device for calibration measurements and subsequent breath analysis. The new sensor system provided a 3σ detection limit of 8.3 ppbV and an NNEA of 1.4E-9 Wcm-1Hz-0.5. In terms of the performed breath analysis measurements, 12 out of 13 fell within the error margin of the photoacoustic measurement system, demonstrating the reliability of the measurements in the field.

Wavelength dependency and photosensitizer effects in UV-LED photodegradation of iohexol

Iodinated X-ray contrast media (ICM) are ubiquitously present in water sources and challenging to eliminate using conventional processes, posing a significant risk to aquatic ecosystems. Ultraviolet light-emitting diodes (UV-LED) emerge as a promising technology for transforming micropollutants in water, boasting advantages such as diverse wavelengths, elimination of chemical additives, and no induction of microorganisms' resistance to disinfectants. The research reveals that iohexol (IOX) degradation escalates as UV wavelength decreases, attributed to enhanced photon utilization efficiency. Pseudo-first-order rate constants (kobs) were determined as 3.70, 2.60, 1.31 and 0.65 cm2 J-1 at UV-LED wavelengths of 255, 265, 275 and 285 nm, respectively. The optical properties of dissolved organic matter (DOM) and anions undeniably influence the UV-LED photolysis process through photon competition and the generation of reactive substances. The influence of Cl- on IOX degradation was insignificant at UV-LED 255, but it promoted IOX degradation at 265, 275 and 285 nm. IOX degradation was accelerated by ClO2-, NO3-and HA due to the formation of various reactive species. In the presence of NO3-, the kobs of IOX followed the order: 265 > 255 > 275 > 285 nm. Photosensitizers altered the spectral dependence of IOX, and the intermediate photoactivity products were detected using electron spin resonance. The transformation pathways of IOX were determined through density functional theory calculations and experiments. Disinfection by-products (DBPs) yields of IOX during UV-LED irradiation decreased as the wavelength increased: 255 > 265 > 275 > 285 nm. The cytotoxicity index value decreased as the UV-LED wavelength increased from 255 to 285 nm. These findings are crucial for selecting the most efficient wavelength for UV-LED degradation of ICM and will benefit future water purification design.

Design and Performance Evaluation of a Deep Ultraviolet LED-Based Ozone Sensor for Semiconductor Industry Applications

Ozone (O3) is a critical gas in various industrial applications, particularly in semiconductor manufacturing, where it is used for wafer cleaning and oxidation processes. Accurate and reliable detection of ozone concentration is essential for process control, ensuring product quality, and safeguarding workplace safety. By studying the UV absorption characteristics of O3 and combining the specific operational needs of semiconductor process gas analysis, a pressure-insensitive ozone gas sensor has been developed. In its optical structure, a straight-through design without corners was adopted, achieving a coupling efficiency of 52% in the gas chamber. This device can operate reliably in a temperature range from 0 °C to 50 °C, with only ±0.3% full-scale error across the entire temperature range. The sensor consists of a deep ultraviolet light-emitting diode in a narrow spectrum centered at 254 nm, a photodetector, and a gas chamber, with dimensions of 85 mm × 25 mm × 35 mm. The performance of the sensor has been meticulously evaluated through simulation and experimental analysis. The sensor's gas detection accuracy is 750 ppb, with a rapid response time (t90) of 7 s, and a limit of detection of 2.26 ppm. It has the potential to be applied in various fields for ozone monitoring, including the semiconductor industry, water treatment facilities, and environmental research.

Microplastics as potential barriers to ultraviolet light emitting diode inactivation of MS2 bacteriophage: Influence of water-quality parameters

Microplastics have emerged as a concerning contaminant in drinking water sources, potentially interacting with pathogenic microorganisms and affecting the disinfection processes. In this study, MS2 was selected as an alternative for the human enteric virus. The influence of microplastics polyvinylchloride (MPs-PVC) on ultraviolet light emitting diode (UV-LED) inactivation of MS2 was investigated under various water chemistry conditions, such as MPs-PVC concentration, pH, salinity, and humic acid concentration. The results revealed that higher concentrations of MPs-PVC led to the reduced inactivation of MS2 by decreased UV transmittance, hindering the disinfection process. Additionally, the inactivation efficiency of MS2 in the presence of MPs-PVC was influenced by pH, and acidic solution (pH at 4, 5, and 6) exhibited higher efficiency compared to alkaline solution (pH at 8 and 9) and neutral solution (pH at 7). The low Na+ concentrations (0-50 mM) had a noticeable effect on MS2 inaction efficiency in the presence of MPs-PVC, while the addition of Ca2+ posed an insignificant effect due to the preferential interaction with MPs-PVC. Furthermore, the inactivation rate of MS2 initially increased and then decreased with increasing the concentration of humic acid, which was significantly different without MPs-PVC. These findings shed light on the complex interactions between MPs-PVC and MS2 in the UV-LED disinfection process under various water-quality parameters, contributing to drinking water safety and treatment.

Comparison of the impact of UV-light emitting diode and UV lamp at pilot-plant scale level on quality parameters and consumer perception of fresh chicken meat

The present study compared the impact of two UV light devices: conventional UV lamp and UV-LED on the colour, pH, lipid and protein oxidation of fresh chicken breast meat aerobically stored at 4 °C for 10 days. Lipid oxidation was the most impacted quality attribute in UV lamp treated meat, unlike UV-LED that showed no effect compared to non-treated meat. Slight changes were observed in colour, pH and protein oxidation of chicken samples subjected to UV lamp and UV-LED. To evaluate these changes from a consumer perspective, the different treatment samples were stored at 4 °C for 3 days and colour likeness, odour likeness and overall appearance were assessed by consumer sensory analysis. However, alterations in quality parameters of chicken meat caused by UV light did not decrease overall acceptance in the sensory analysis. UV-LED was the preferred chicken meat by the participants, even compared to non-treated meat.

Effect of ozonation and UV-LED combination on simultaneous removal of toxic elements during electrocoagulation

Cyanide and heavy metals pose significant risks as contaminants in certain industrial effluents. This study aims to concurrently eliminate cyanide and specific heavy metals from synthetic wastewater resembling gold processing effluent, employing an improved electrocoagulation method incorporating ozone and UV-LED. The investigation delves into the effects of pH, electrode type, current density, reaction time, and ozonation. The findings revealed notable removal efficiencies: 98% for cyanide, 76% for nickel, 85% for copper, and 84% for zinc when utilizing a stainless steel electrode as the cathode. Optimal removal rates were achieved at 94% for cyanide, 93% for copper, 92% for zinc, and 83% for nickel, employing the UV-LED-ozone technique with an ozonation flow rate of 4 mg/s at pH = 10. Notably, when Al-Gr-SS-Fe electrodes and a current of 15 mA/cm2 were applied, these removal efficiencies were observed. Therefore, the most favorable conditions for the concurrent removal of pollutants from synthetic wastewater involved maintaining a pH of 10, utilizing SS-Fe as anode and Al-Gr as cathode electrodes, and employing a current density of 15 mA/cm2. The addition of ozonation with a flow rate of 4 mg/s, along with UV-LED, further enhanced the removal process. In summary, it can be inferred that the enhanced electrocoagulation method outperformed conventional electrocoagulation, leading to increased elimination of cyanide and selected heavy metals.

The efficiency of UV light-emitting diodes (UV-LED) in decontaminating Campylobacter and Salmonella and natural microbiota in chicken breast, compared to a UV pilot-plant scale device

This study investigated the combined effect of Ultraviolet (UV) light-emitting diode (LED) technology treatment with refrigerated storage of chicken breast meat over 7 days on Campylobacter jejuni, Salmonella enterica serovar Typhimurium, total viable counts (TVC) and total Enterobacteriaceae counts (TEC). An optimised UV-LED treatment at 280 nm for 6 min decreased inoculated S. Typhimurium and C. jejuni populations by 0.6-0.64 log CFU/g, and TVC and TEC population by 1-1.2 log CFU/g in chicken samples. During a 7-day storage at 4 °C, a 0.73 log reduction in C. jejuni was achieved compared with non-treated samples. Moreover, the UV-LED effectiveness to reduce TVC and TEC during refrigerated storage was compared with a conventional UV lamp and a similar efficiency was observed. The impact of UV-LED and UV lamp devices on the microbial community composition of chicken meat during storage was further examined using 16 S rRNA gene amplicon sequencing. Although similar bacterial reductions were observed for both technologies, the microbial communities were impacted differently. Treatment with the UV conventional lamp increased the proportion of Brochothrix spp. In meat samples, whilst Photobacterium spp. Levels were reduced.

Low-cost test rig for characterization of photocatalytic planar materials using photonically sized UV-A LED light sources

In the presented studies, a system for the characterization of planar photocatalysts was developed and tested. In the system, reference substances can be studied online with regard to their degradability and adsorption on photocatalytic materials. In order to perform accurate calculations of the quantum and photon efficiency of the catalysts, the LED arrays used were adjusted in their spacing by simulations so that a homogeneous light field is imaged on the catalysts. The system was tested with respect to measurement accuracy and reproducibility and the photocatalytic degradation of methylene blue, methyl orange and rhodamine B was investigated. Exemplarily, the reaction kinetics, photolysis and adsorption on the tested photocatalysts were determined for these compounds and the calculation was presented in detail. The exact construction plans and circuits as well as the sensors and their programming are presented in detail and should encourage other scientists to replicate the experimental setup, since especially in the field of photocatalysis research, often the results of publications cannot be compared with each other.

Efficacy of UV and UV-LEDs Irradiation Models for Microbial Inactivation Applicable to Automated Sterile Drug Compounding

LEDs development has attracted attention over conventional mercury lamps for the tiny size, high efficiency, long lifetime, low operating temperature. The antimicrobial effectiveness of traditional UV-lamps radiation (wavelength of 254 nm) compared to UV-C LEDs (LED1 wavelength range 275-286 nm and LED2 range 260-270 nm) was carried out, for possible applications to automated sterile drug compounding. The UV lamp and the tested UV-LED devices remarkably reduced microbial load, following a time-dose response, but the best performance was evidenced by LED1, which guaranteed the complete inactivation of high concentrations of bacteria, yeasts, and spores at doses between 200 and 2000 J/m2.

UV-LED silicon carbide composite photocatalytic membrane reactor for the degradation of organic contaminants

The utilization of membranes in the water industry has been growing rapidly; however, the technology still experiences problems with fouling. A potential solution is to immobilize photocatalyst particles on the surface of the membranes to encourage in situ degradation of the organic contaminants contributing to the fouling. In this study, we developed a photocatalytic membrane (PM) by coating a silicon carbide membrane with Zr/TiO₂ sol. The performance of the PM in degrading different concentrations of humic acid was evaluated comparatively under UV irradiation of two wavelengths, 275 and 365 nm. The results indicated that (i) the PM achieved high levels of humic acid degradation, (ii) the photocatalytic activity of the PM reduced the formation of fouling and hence the loss of permeability, (iii) the formation of fouling was reversible; no trace of fouling was observed after cleaning, and (iv) the PM showed high durability during multiple rounds of operation.

The Attenuation of Microbial Reduction in Blueberry Fruit Following UV-LED Treatment

Ultraviolet-C (UV-C) irradiation is a well-recognized technology for improving blueberry postharvest quality, and previous literature indicates that it has the potential for dual-use as an antimicrobial intervention for this industry. However, the practicality and feasibility of deploying this technology in fresh blueberry fruit are significantly hindered by the shadowing effect occurring at the blossom-end scar of the fruit. The purpose of this study was to determine if treating the blueberry fruit within a chamber fitted with UV-Light Emitting Diodes (LEDs) emitting a peak UV-C at 275 nm could minimize this shadowing and result in improved treatment efficacy. Ten blueberry fruits were dip-inoculated with E. coli at a concentration of 10⁵ CFU/mL and irradiated within the system at doses of 0, 1.617, 3.234, 9.702, and 16.17 mJ/cm² (0, 30, 60, 180, and 300 s). Statistical analysis was performed to characterize the extent of microbial survival as well as the UV-C inactivation kinetics. A maximum of 0.91-0.95 log reduction was observed, which attenuated after 60 s of treatment. The microbial inactivation and survival were thus modeled using the Geeraerd-tail model in Microsoft Excel with the GInaFIt add-in (RMSE = 0.2862). Temperatures fluctuated between 23 ± 0.5°C and 39.5°C ± 0.5°C during treatment but did not statistically impact the treatment efficacy (P = 0.0823). The data indicate that the design of a UV-LED system may improve the antimicrobial efficacy of UV-C technology for the surface decontamination of irregularly shaped fruits, and that further optimization could facilitate its use in the industry.

Acetaminophen degradation in aqueous solution by the UV-LED-EC/Cl2 process

In this study, electrochemically generated free chlorine (EC/Cl2) was activated by UV irradiation with a light emitting diode (LED) lamp at 275 nm to degrade acetaminophen (AAP, 2 μM) in aqueous solution. The potential at a RuO2-IrO2/Ti plate anode was set at 1.5 V vs. the Ag/AgCl electrode. Chlorine was in situ generated in the presence of Cl at the anode and then it was transformed into various active species such as OH and reactive chlorine species (RCS) under UV-LED irradiation. The degradation of AAP was investigated using batch tests, evaluating the influence of different experimental conditions such as NaCl concentration, phosphate buffer saline concentration, irradiation time and solution pH, keeping constant the UV-LED power and temperature. Results show that AAP could be completely degraded by the hybrid process with a high mineralization ratio (73%), and the degradation process followed a pseudo-first-order kinetics. The value of the Electric Energy per Order (EEO) = 1.272 kWh m3 order?, which is lower than the energy consumption of some other UV-based processes for AAP degradation. Adding 1 mM HCO3 ions slightly decreased the rate of AAP degradation. Luminescent bacteria experiment revealed that the acute toxicity of the reacted solution could be greatly reduced and the ecological risk was effectively abated. The scavenging assay shows that RCS plays a key role in the AAP degradation. The intermediate products were identified, and possible degradation routes were proposed. The system can advantageously replace conventional UV mercury lamp based ones in the degradation of microorganic pollutants.

Protocol for UVC uridine actinometry

Uridine contains the chromophore uracil, a base forming part of RNA. In the range 240-290 nm, the absorption spectra of uridine and DNA are very similar and correspond to the spectral inactivation sensitivity of almost all microorganisms. This makes the uridine (absorption maximum 262 nm) an ideal actinometer for determining the germicidal photon flux in the range of 240 to 290 nm. Uridine actinometry is a simple, environmental-friendly, and easy-to-operate actinometry. Thanks to the uridine absorbance spectrum, it was found to be a perfect fit for the photon flux validation of UVC systems. Conventional UV disinfection systems are generally based on low-pressure (LP) mercury lamps which emit at 254 nm. On the other hand, UV light-emitting diodes (UV-LEDs) are a relatively new source of UV light for water treatment, emitting at various wavelengths. This protocol suggests an accurate, simple, easy to operate and straightforward way to determine the photon flux of UVC systems. Contain between 1 and 3 bullet points highlighting the customization rather than the steps of the procedure.•Because of the uridine absorbance spectrum, it is an ideal actinometer for photon flux validation of UVC systems.•Initial uridine concentration and photoproduct absorbance impact the kinetic order and quantum yield.•The protocol for UVC uridine actinometry is appropriate for UV-LP and UV-LED sources for water disinfection.

Contribution of filtration and photocatalysis to DOM removal and fouling mechanism during in-situ UV-LED photocatalytic ceramic membrane process

The use of ceramic membranes and ultraviolet light-emitting diodes (UV-LEDs) has advanced the application of photocatalytic membrane for water treatment. We systematically evaluated the contribution of filtration and photocatalysis to dissolved organic matter (DOM) removal and fouling mechanism during in-situ UV-LED photocatalytic ceramic membrane filtration. The results showed that physical rejection primarily led to removal of 4-15 kDa molecules and photocatalysis further increased the removal of 1-4 kDa molecules, causing small sized microbial humic-like or protein-like materials in the permeate. In-situ UV-LED photocatalysis had an excellent effect on membrane fouling mitigation regardless of DOM sources. The dominant fouling mechanism changed from partial blockage to gel layer formation with increasing Ca²⁺ concentration but did not change with UV treatment. Correlation analysis revealed that the removal of 1-4 kDa molecules contributed to the mitigation of both reversible and irreversible fouling resistance, and the small molecules were the major cause of irreversible fouling resistance. Removal of 1-4 kDa terrestrial humic acid-like contributed to the pore blockage mechanism for synthetic water. Removal of 4-15 kDa protein-like materials was closely correlated to the pore blockage mechanism for real water. Trihalomethanes (THMs) and haloacetic acids (HAAs) formation potential (FP) were both significantly reduced after photocatalytic ceramic membrane process, but precursors of nitrogenous disinfection by-products (N-DBPs) with high toxicity were not removed by filtration or by photocatalysis, which deserves attention. Membrane rejection made higher contribution to better DBPFP control than photocatalysis. This study provides novel insights into the impact of UV-LED on DOM removal, DBPFP control and fouling mitigation, promoting the development of photocatalytic ceramic membrane filtration.

Degradation of iopromide during the UV-LED/chlorine reaction: Effect of wavelength, radical contribution, transformation products, and toxicity

Three different UV-LED wavelengths (265, 310, and 365 nm) were used in the UV-LED/chlorine reaction to investigate the degradation mechanism of iopromide (IPM) at different wavelengths, a representative iodinated contrast media compound. The degradation rate (k'_IPM) increased from pH 6-8 at 265 nm, but, decreased as the pH increased up to 9 at 310 nm and 365 nm. Radical scavenging experiments showed that reactive chlorine species (RCS) are the dominant radical species at all wavelengths, but a higher contribution of OH• was observed at lower pH and longer wavelengths. The contribution of RCS decreased but the contribution of OH• increased as the wavelength increased. Among RCS, the largest contribution was found to be ClO•. Total nine transformation products (TPs) were identified by LC-QTOF-MS during the UV-LED/chlorine reaction at 265 nm. Based on the identified TPs and their time profiles, we proposed a degradation pathway of IPM during UV-LED/chlorine reaction. The Microtox test using V. fischeri showed that no significant increase in toxicity was observed at all wavelengths. The synergistic effect of UV-LED and chlorine was greater at a higher wavelength by the electrical efficiency per order (EEO) calculation.

Insight into UV-LED/PS/Fe(Ⅲ) and UV-LED/PMS/Fe(Ⅲ) for p-arsanilic acid degradation and simultaneous arsenate immobilization

As a feed additive, p-arsanilic acid (p-ASA) is hardly metabolized in animal bodies and is excreted chemically unchanged via feces and urine, which can be transformed into more toxic inorganic arsenic species and other organic by-products upon degradation in the aquatic environment. In this study, UV-LED/persulfate (PS)/Fe(Ⅲ) and UV-LED/peroxymonosulfate (PMS)/Fe(Ⅲ) processes were developed to remove p-ASA and immobilize the formed inorganic arsenic via tuning solution pH. UV-LED/PMS/Fe(Ⅲ) (90.8%) presented the best performance for p-ASA degradation at pH 3.0, and the p-ASA degradation in these processes both followed the pseudo-first-order kinetics. The ∙OH played the major role in UV-LED/PS/Fe(Ⅲ) and UV-LED/PMS/Fe(Ⅲ) systems. Solution pH greatly affected the p-ASA degradation and the maximum removal can be achieved at pH 3.0 due to the presence of more Fe(OH)(H₂O)₅²⁺. The dosages of Fe(III) and PMS (PS), SO₄^2- and HCO₃^- significantly influenced the performance of p-ASA oxidation, while HA, Cl^- and NO₃^- slightly affected the p-ASA degradation. According to quantum chemical calculation, radical addition on the C atom in the C-As bond of p-ASA was corroborated to be the dominant reaction pathway by SO₄∙^- and ∙OH. Additionally, the reactive sites and reasonable degradation pathways of p-ASA were proposed based on DFT calculation and HPLC/MS analysis. The release of inorganic arsenic in both processes can be effectively immobilized and the toxicity of the reaction solution dramatically reduced by adjusting solution pH to 6.0. UV-LED/PMS/Fe(Ⅲ) process was found to be more cost-effective than UV-LED/PS/Fe(Ⅲ) process at the low oxidant dosages.

A novel UV-LED hydrogen peroxide electrochemical photoreactor for point-of-use organic contaminant degradation

The degradation of organic contaminants is typically achieved by exposure of hydrogen peroxide (H₂O₂) containing influent to ultraviolet (UV) lamps as the source of radiation that can convert H₂O₂ to hydroxyl radicals (·OH), which oxidize organic pollutants. However, two factors prevent this process from being scaled down: the need to introduce H₂O₂, which requires special handling, and the use of bulky UV lamps, which have a high electric power consumption. In this work, an electrochemical cell was developed for the efficient in situ generation of H₂O₂ from water and atmospheric oxygen in a process called a two-electron oxygen reduction reaction (2e-ORR), so that the external addition of H₂O₂ is no longer needed. Moreover, the electrochemical cell was equipped with ultraviolet light-emitting diodes (UV-LEDs) to convert H₂O₂ to ·OH. The reactor exhibited a current efficiency of ∼90% for the H₂O₂ production at a flow rate of 50 mL min^-1. The degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied at 277 nm based on different operational parameters, such as UV fluence rate, initial concentration, and initial pH. A high degradation of >70% was obtained at a UV output of 900 mW. Our approach, the first of its kind, has novel features applied, including: optimal radiation distribution in the reactor by applying a new UV source, UV-LEDs that offer much more control for the radiation profile in the reaction system compared to traditional UV lamps, controlled hydrodynamics by implementing special flow channels to provide a more uniform residence time and offer enhanced mixing, and integrating UV reactor and electrochemical cell in a single unit which could lead to superior performance and space efficiency of the device. These features make the device very suitable for point-of-use (POU) water treatment applications to eliminate both microbial and chemical contaminants.

Insights into the wavelength-dependent photolysis of chlorite: Elimination of carbamazepine and formation of chlorate

Simultaneous removal of chlorite (ClO₂^-) and organic micro-pollutants (OMPs) by the irradiation of UV is a novel process. In this study we used UV light emitting diode (UV-LED) as a new UV source to systematically investigate the effect of UV wavelength (255, 285, 365 nm) on the simultaneous removal of carbamazepine (CBZ) and ClO₂^-. Removal of both CBZ and ClO₂^- followed the order of 255, 285, and 365 nm. Formation of hydroxyl radical and reactive chlorine species (RCS) were confirmed during the photolysis of ClO₂^- using probe compounds. RCS were always the predominant contributor to the degradation of CBZ in UV-LED/ClO₂^- system. The impacts of ClO₂^- dosage, pH, bicarbonate/carbonate (HCO₃^-/CO₃^2-), and the effect of natural organic matter (NOM) on CBZ degradation were also evaluated. This study identified the products produced by CBZ through possible degradation pathways during the transformation process. Further, the amount of ClO₂^- may affect the amount of chlorate produced in UV/ClO₂^- system. Overall, our research provides an in-depth analysis of the effects of UV wavelength on the simultaneous removal of ClO₂^- and OMPs in water.

A Novel UVA/ClO2 Advanced Oxidation Process for the Degradation of Micropollutants in Water

Ultraviolet (UV)-based advanced oxidation processes (AOPs) are increasingly used for the degradation of micropollutants in water and wastewater. This study reports a novel UVA/chlorine dioxide (ClO₂) AOP based on the photolysis of ClO₂ using energy-efficient UV radiation sources in the UVA range (e.g., UVA-LEDs). At a ClO₂ dosage of 74 μM (5.0 mg L^-1 as ClO₂) and a UV fluence at 47.5 mJ cm^-2, the UVA₃₆₅/ClO₂ AOP generated a spectrum of reactive species, including chlorine oxide radicals (ClO^•), chlorine atoms (Cl^•), hydroxyl radicals (HO^•), and ozone at a concentration of ∼10^-13, ∼10^-15, ∼10^-14, and ∼10^-7 M, respectively. A kinetic model to simulate the reactive species generation in the UVA₃₆₅/ClO₂ AOP was established, validated against the experimental results, and used to predict the pseudo-first-order rate constants and relative contributions of different reactive species to the degradation of 19 micropollutants in the UVA₃₆₅/ClO₂ AOP. Compared to the well-documented UVC₂₅₄/chlorine AOP, the UVA₃₆₅/ClO₂ AOP produced similar levels of reactive species at similar oxidant dosages but was much less pH-dependent and required much lower energy input, with much lower formation of chloro-organic byproducts and marginal formation of chlorite and chlorate.

Bisphenol S degradation via persulfate activation under UV-LED using mixed catalysts: Synergistic effect of Cu-TiO2 and Zn-TiO2 for catalysis

A photocatalyst composed of Zn-TiO₂ and Cu-TiO₂ through simple physical mixing was used to activate persulfate(PS) for Bisphenol S (BPS) degradation. Zn-TiO₂ and Cu-TiO₂ were prepared with a sol gel method and were characterized by X-ray diffraction (XRD), Raman, Transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The two catalysts have shown an obvious synergistic effect in the photocatalytic degradation process. When 5 mM persulfate and 0.3 g/L catalyst were used, the removal rate of mixed catalyst (0.2 g/L Zn-TiO₂ and 0.1 g/L Cu-TiO₂) is 100 % in 18 min, which is significantly better than that of 0.3 g/L Zn-TiO₂(58 %) and 0.3 g/L Cu-TiO₂(90 %). Typically, the effects of various operation parameters, including the ratio of Cu-TiO₂/Zn-TiO₂, catalyst dosage, persulfate dosage, initial concentration of BPS, and initial solution pH, were examined. Reactive oxygen species (ROS) in the UV/mixed catalyst/PS process was identified by scavenger and electron paramagnetic resonance (EPR) tests. The superoxide radicals generated by both Zn-TiO₂ and the hydrolysis of persulfate in the system could accelerate the Cu (II)/Cu(I) redox cycles and results in the synergistic effect. This study proposed a new and effective way to improve the reaction by simply combining two catalysts, and unraveled the mechanism behind the synergistic effect, which could provide new ideas to use the catalyst more effectively for wastewater treatment or other areas.

Recent Update on UV Disinfection to Fulfill the Disinfection Credit Value for Enteric Viruses in Water

Ultraviolet (UV) radiation alone or in combination with other oxidation processes is increasingly being considered for water disinfection because of stringent regulatory requirements for pathogen inactivation. To fulfill this requirement, an appropriate UV dose or fluence (mJ/cm²) is applied to combat enteric viruses in surface or treated water. There is a need for a cumulative review on the effectiveness of current and emerging UV technologies against various types of human enteric viruses. We extracted the kinetics data from 52 selected experimental studies on enteric virus inactivation using low pressure (LP-UV), medium pressure (MP-UV), UV-LED, and advanced oxidation processes (AOPs) and applied a simple linear regression analysis to calculate the range of UV fluence (mJ/cm²) needed for 4-log₁₀ inactivation. The inactivation of adenoviruses with LP-UV, MP-UV, and UV/H₂O₂ (10 mg/L) required the highest fluence, which ranged from 159 to 337, 45, and 115 mJ/cm², respectively. By contrast, when using LP-UV, the inactivation of other enteric viruses, such as the Caliciviridae and Picornaviridae family and rotavirus, required fluence that ranged from 19 to 69, 18 to 43, and 38 mJ/cm², respectively. ssRNA viruses exhibit higher sensitivity to UV radiation than dsRNA and DNA viruses. In general, as an upgrade to LP-UV, MP-UV is a more promising strategy for eliminating enteric viruses compared to AOP involving LP-UV with added H₂O₂ or TiO₂. The UV-LED technology showed potential because a lower UV fluence (at 260 and/or 280 nm wavelength) was required for 4-log₁₀ inactivation compared to that of LP-UV for most strains examined in this critical review. However, more studies evaluating the inactivation of enteric viruses by means of UV-LEDs and UV-AOP are needed to ascertain these observations.

Enhanced photocatalytic activity of efficient magnetically recyclable core-shell nanocomposites on 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) degradation under UV-LED irradiation

The congener polychlorinated biphenyls (PCBs) are one of the of persistent organic pollutant compounds that increase lifestyle-related diseases, such as diabetes, obesity, and cancer. So, 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153), which is one of the most common PCB contaminants in nature, was selected as a model compound to study the photocatalytic degradation of Fe₃O₄@SiO₂@TiO₂ core-shell structure. In this work, Fe₃O₄@SiO₂@TiO₂ nanocomposite was synthesized and characterized using transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) techniques. Then, the effect of parameters such as catalyst dosage, initial concentration of PCB 153, solution pH, amount of H₂O₂, and kind of co-solvent on photocatalytic degradation of PCB 153 by the synthesized nanocomposite was investigated. The high degradation efficiency of Fe₃O₄@SiO₂@TiO₂ nanocomposite, which was 96.5%, was obtained at 4 g/l of the catalysts, 4 ppm of PCB 153, pH 5, 20 mM H₂O₂, 2 h of reaction time, and acetone as a cosolvent. Also, the rate of mineralization for Fe₃O₄@SiO₂@TiO₂ nanocomposite with H₂O₂ and UV-LED irradiation was 75.3% which had a significant efficiency compared to control experiments. Moreover, the mentioned photocatalysts are possible to be reused through exposing to external magnetic field, with insignificant decrease in the catalytic activity even after 6 cycles. The photocatalytic degradation process has an effective and environmental friendly effect on the degradation of organic pollutants.

Electrospun Semi-Alicyclic Polyimide Nanofibrous Membrane: High-Reflectance and High-Whiteness with Superior Thermal and Ultraviolet Radiation Stability for Potential Applications in High-Power UV-LEDs

Polymeric nanofibrous membranes (NFMs) with both high whiteness and high thermal and ultraviolet (UV) stability are highly desired as reflectors for ultraviolet light-emitting diodes (UV-LEDs) devices. In the current work, a semi-alicyclic and fluoro-containing polyimide (PI) NFM with potential application in such kinds of circumstances was successfully fabricated from the organo-soluble PI resin solution via a one-step electrospinning procedure. In order to achieve the target, a semi-alicyclic PI resin was first designed and synthesized from an alicyclic dianhydride, 3,4-dicarboxy-1,2,3,4,5,6,7,8-decahydro-1-naphthalenesuccinic dianhydride (or hydrogenated tetralin dianhydride, HTDA), and a fluoro-containing diamine, 2,2-bis[4-(4-amino-phenoxy)phenyl]hexafluoropropane (BDAF), via an imidization procedure. The derived PI (HTDA-BDAF) resin possessed a number-average molecular weight (M_n) higher than 33,000 g/mol and was highly soluble in polar aprotic solvents, such as N,N-dimethylacetamide (DMAc). The electrospinning solution was prepared by dissolving the PI resin in DMAc at a solid content of 25–35 wt%. For comparison, the conventional high-whiteness polystyrene (PS) NFM was prepared according to a similar electrospinning procedure. The thermal and UV stability of the derived PI and PS NFMs were investigated by exposure under the UV-LED (wavelength: 365 nm) irradiation. Various thermal evaluation results indicated that the developed PI (HTDA-BDAF) NFM could maintain both the high reflectance and high whiteness at elevated temperatures. For example, after thermal treatment at 200 °C for 1 h in air, the PI (HTDA-BDAF) NFM exhibited a reflectance at a wavelength of 457 nm (R₄₅₇) of 89.0%, which was comparable to that of the pristine PI NMF (R₄₅₇ = 90.2%). The PI (HTDA-BDAF) NFM exhibited a whiteness index (WI) of 90.88, which was also close to that of the pristine sample (WI = 91.22). However, for the PS NFM counterpart, the R₄₅₇ value decreased from the pristine 88.4% to 18.1% after thermal treatment at 150 °C for 1 h, and the sample became transparent. The PI NFM maintained good optical and mechanical properties during the high dose (2670 J/cm²) of UV exposure, while the properties of the PS NFM apparently deteriorated under the same UV aging.

Study of the Photodegradation of PBDEs in Water by UV-LED Technology

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants that can arrive to water bodies from their use as flame retardants in a wide range of applications, such as electric and electronic devices or textiles. In this study, the photodegradation of PBDEs in water samples when applying UV-LED radiation was studied. Irradiation was applied at three different wavelengths (255 nm, 265 nm and 285 nm) and different exposure times. The best degradation conditions for spiked purified water samples were at 285 nm and 240 min, resulting in degradations between 67% and 86%. The optimized methodology was applied to real water samples from different sources: river, marine, wastewater (effluent and influent of treatment plants) and greywater samples. Real water samples were spiked and exposed to 4 hours of irradiation at 285 nm. Successful photodegradation of PBDEs ranging from 51% to 97% was achieved for all PBDE congeners in the different water samples with the exception of the marine one, in which only a 31% of degradation was achieved.

Rapid Inactivation of SARS-CoV-2 Variants by Continuous and Intermittent Irradiation with a Deep-Ultraviolet Light-Emitting Diode (DUV-LED) Device

More than 1 year has passed since social activities have been restricted due to the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). More recently, novel SARS-CoV-2 variants have been spreading around the world, and there is growing concern that they may have higher transmissibility and that the protective efficacy of vaccines may be weaker against them. Immediate measures are needed to reduce human exposure to the virus. In this study, the antiviral efficacy of deep-ultraviolet light-emitting diode (DUV-LED) irradiation (280 ± 5 nm, 3.75 mW/cm2) against three SARS-CoV-2 variants was evaluated. For the B.1.1.7, B.1.351, and P.1 variant strains, irradiation of the virus stocks for 1 s resulted in infectious titer reduction rates of 96.3%, 94.6%, and 91.9%, respectively, and with irradiation for 5 s, the rates increased to 99.9%, 99.9%, and 99.8%, respectively. We also tested the effect of pulsed DUV-LED irradiation (7.5 mW/cm2, duty rate: 50%, frequency: 1 kHz) under the same output conditions as for continuous irradiation and found that the antiviral efficacy of pulsed and continuous irradiation was the same. These findings suggest that by further developing and optimizing the DUV-LED device to increase its output, it may be possible to instantly inactivate SARS-CoV-2 with DUV-LED irradiation.

UV-LED as a New Emerging Tool for Curable Polyurethane Acrylate Hydrophobic Coating

The elimination of mercury, low energy consumption, and low heat make the ultraviolet light-emitting diode (UV-LED) system emerge as a promising alternative to conventional UV-mercury radiation coating. Hence, a series of hydrophobic coatings based on urethane acrylate oligomer and fluorinated monomer via UV-LED photopolymerisation was designed in this paper. The presence of fluorine component at 1160 cm-1, 1235 cm-1, and 1296 cm-1 was confirmed by Fourier Transform Infra-Red spectroscopy. A considerably high degree C=C conversion (96-98%) and gel fraction (95-93%) verified the application of UV-LED as a new technique in radiation coating. It is well-accepted that fluorinated monomer can change the surface wettability as the water contact angle of the coating evolved from 88.4° to 121.2°, which, in turn, reduced its surface free energy by 70.5%. Hence, the hydrophobicity of the coating was governed by the migration of the fluorine component to the coating surface as validated by scanning electron and atomic force microscopies. However, above 4 phr of fluorinated monomer, the transparency of the cured coating examined by UV-visible spectroscopy experienced approximately a 16% reduction. In summary, the utilisation of UV-LED was a great initiative to develop green aspect in photopolymerisation, particularly in coating technology.

Photodecomposition of pharmaceuticals and personal care products using P25 modified with Ag nanoparticles in the presence of natural organic matter

The presence of pharmaceuticals and personal care products (PPCPs) in water remains a concern due to their potential threat to environmental and human health. Advanced oxidation processes (AOPs) have been receiving attention in water treatment studies to remove PPCPs. However, most studies have been focused on pure water containing a limited number of substances. In this study, the photocatalytic efficiency of commercially available titanium dioxide nanoparticles (P25) and P25 modified by silver nanoparticles (Ag-P25) were compared for their ability to degrade 23 target PPCPs (2 μg L^-1) in realistic water matrices containing natural organic matter (Suwanee River NOM, 6.12 mg L^-1). The experiments were completed under ultraviolet-light emitting diode (UV-LED) illumination at 365 and 405 nm wavelengths, with the latter representing visible light exposure. Under 365 nm UV-LED treatment, 99% of the PPCPs were removed using both P25 and Ag-P25 photocatalysts within 180 min of the treatment duration. The number of PPCPs removed dropped to 57% and 53% for P25 and Ag-P25 respectively under the 405 nm UV-LED irradiation. Dissolved organic carbon (DOC) and UV absorbance at 254 nm (UV254) measured at the end of the experiment indicated that the aromatic fraction of NOM was preferentially removed from the water matrix. Also, Ag-P25 was more effective in DOC removal than P25. The relationships of removal rate constants with physico-chemical properties of the substances were also determined. The molecular weight and charge were strongly associated with removal, with the former and the latter being positively and negatively correlated with the rate constants. The results of this work indicate that Ag-P25 is a promising photocatalyst to degrade persistent substances such as PPCPs and NOM even if they are present in a complex water matrix. The properties of individual substances can also be employed as an indication of their removal using this technology.

Photocatalytic removal of the cyanobacterium Microcystis aeruginosa PCC7813 and four microcystins by TiO2 coated porous glass beads with UV-LED irradiation

Cyanobacteria and their toxic secondary metabolites are a challenge in water treatment due to increased biomass and dissolved metabolites in the raw water. Retrofitting existing water treatment infrastructure is prohibitively expensive or unfeasible, hence 'in-reservoir' treatment options are being explored. In the current study, a treatment system was able to photocatalytically inhibit the growth of Microcystis aeruginosa and remove released microcystins by photocatalysis using titanium dioxide coated, porous foamed glass beads and UV-LEDs (365 nm). A 35% reduction of M. aeruginosa PCC7813 cell density compared to control samples was achieved in seven days. As a function of cell removal, intracellular microcystins (microcystin-LR, -LY, -LW, and -LF) were removed by 49% from 0.69 to 0.35 μg mL^-1 in seven days_. Microcystins that leaked into the surrounding water from compromised cells were completely removed by photocatalysis. The findings of the current study demonstrate the feasibility of an in-reservoir treatment unit applying low cost UV-LEDs and porous foamed beads made from recycled glass coated with titanium dioxide as a means to control cyanobacteria and their toxins before they can reach the water treatment plant.

Removal of micropollutants in drinking water using UV-LED/chlorine advanced oxidation process followed by activated carbon adsorption

This study investigated the removal of three selected micropollutants (i.e., bisphenol A, diclofenac and caffeine) in drinking water using the UV-LED/chlorine advanced oxidation process (AOP) followed by activated carbon adsorption. The degradation of bisphenol A, diclofenac and caffeine was predominantly contributed by chlorination (>60%), direct UV photolysis (>80%) and radical oxidation (>90%), respectively, during the treatment by the UV-LED/chlorine AOP at three tested UV wavelengths (i.e., 265, 285 and 300 nm). The most effective UV wavelengths for the degradation of bisphenol A, diclofenac and caffeine were 265, 285 and 300 nm, respectively. The degradation of all the three micropollutants was enhanced with increasing pH from 6 to 8, though the reasons for the pH dependence were different. The residues of the micropollutants and their degradation (by)products were removed by post-adsorption using granular activated carbon (GAC). Interestingly and more importantly, the adsorption rates of the degradation (by)products were 2-3 times higher than the adsorption rates of the corresponding micropollutants, indicating the formation of more adsorbable (by)products after the AOP pre-treatment. The UV-LED/chlorine AOP followed by GAC adsorption provides a multi-barrier treatment system for enhancing micropollutant removal in potable water. The findings also suggest the merit of the sequential use of UV-LEDs followed by GAC in treating chlorine-containing potable water in small-scale water treatment systems (e.g., point-of-use or point-of-entry water purifiers).

Efficacy of ultraviolet light-emitting diodes (UV-LED) at four different peak wavelengths against Cryptosporidium parvum oocysts by inactivation assay using immunodeficient mice

As an alternative to using ultraviolet (UV) lamps, which are made with mercury that is toxic to the environment and human health, UV light-emitting diodes (UV-LEDs) are expected to be effective for inactivating microorganisms in water. Although UV-LEDs have been reported to be effective against bacteria and viruses, the effectiveness of UV-LEDs against Cryptosporidium parasites has not been fully evaluated. As we report here, we have developed an in vivo quantitative inactivation assay for C. parvum oocysts using immunodeficient mice. Using the assay, we evaluated the effectiveness of treatment by UV lamp (254 nm) at approximately 1000 μJ/cm² (for 3 s at a distance of 95 mm) compared to inactivation by commercially available UV-LEDs (with peak wavelengths of 268, 275, 284, and 289 nm). The shed patterns of oocysts after treatment with 284- and 289-nm wavelength UV-LEDs were significantly delayed compared to that after treatment with a UV lamp. These findings provide the first suggestion that UV-LEDs are effective against these parasites, as assessed using commercially available 350-mA UV-LEDs under conditions of fixed exposure distance and time.

Methods of Disinfecting Stethoscopes: Systematic Review

The aim of this systematic review was to investigate the effectiveness of various disinfection methods available for stethoscopes. In March 2019, we performed a search in PubMed and Scopus using the search terms: “reducing stethoscopes contamination” and “disinfection stethoscopes”; the Mesh terms used in PubMed were “Decontamination/methods” or “Disinfection/methods” and “Stethoscopes/microbiology”. Selection criteria were: English language; at least one disinfection method tested. A total of 253 publications were screened. After title, abstract, and full-text analysis, 17 papers were included in the systematic review. Ethanol at 90%, Ethanol-Based Hands Sanitizer (EBHS), triclosan, chlorhexidine, isopropyl alcohol, 66% ethyl alcohol, sodium hypochlorite, and benzalkonium chloride have been proven to lower the presence of bacteria on stethoscopes’ surfaces. In addition, alcohol wipes show effective results. A wearable device emitting ultraviolet C by Light-Emitting Diode (LED) resulted efficacious against common microorganisms involved in Healthcare Associated Infections. The cover impregnated with silver ions seemed to be associated with significantly higher colony counts. Instead, copper stethoscopes surface reduced bacterial load. The disinfection of stethoscopes appears to be essential. There are many valid methods available; the choice depends on various factors, such as the cost, availability, and practicality.

A comparison of dissolved organic matter transformation in low pressure ultraviolet (LPUV) and ultraviolet light-emitting diode (UV-LED)/chlorine processes

This study compared the degradation of dissolved organic matter (DOM) by UV/chlorine advanced oxidation processes (AOPs) with emerging ultraviolet light-emitting diode (UV-LED, 275 nm) and traditional low pressure UV (LPUV, 254 nm) as UV sources. Excitation emission matrix-parallel factor (EEM-PARAFAC) analysis and two-dimensional (2D) correlation gel permeation chromatograph were applied to explore the evolutions of DOM during oxidation processes. The degradation behaviors of DOM indicated by UV absorbance at 254 nm (UV₂₅₄), dissolved organic carbon (DOC), and fluorophores fitted the pseudo-first-order kinetics well. The removal efficiency of DOM was similar under UV-LED and LPUV irradiation alone. However, UV-LED exhibited much higher degradation rates (increased by 29-160%) than LPUV regardless of the tracking variables during UV/chlorine processes. For three PARAFAC components, humic-like fluorescences were preferentially degraded by UV/chlorine oxidation compared with protein-like fluorescence potentially due to the differences of electronic moieties and molecular weight (MW). The decline in UV₂₅₄, DOC, and fluorophores increased with increasing chlorine dosage; linear correlations between those indicators were observed during the two AOPs. Moreover, UV-LED/chlorine could achieve greater extents of MW change. Our study demonstrated that UV-LED could be a superior alternative for the future selection of UV source in the UV/chlorine process.

Investigating the efficiency of α-Bismuth zinc oxide heterostructure composite/UV-LED in methylene blue dye removal and evaluation of its antimicrobial activity

Heterostructured α-Bismuth zinc oxide (α-Bi₂O₃-ZnO) photocatalyst was fabricated by a facile and cost-effective, ultrasound assisted chemical precipitation method followed by hydrothermal growth technique. As synthesized α-Bi₂O₃-ZnO photocatalyst showed enhanced photocatalytic performance for the MB dye degradation in contrast to pure ZnO and α-Bi₂O₃. Light emitting diodes (UV-LED) were used in the experimental setup, which has several advantages over conventional lamps like wavelength selectivity, high efficacy, less power consumption, long lifespan, no disposal problem, no warming-up time, compactness, easy and economic installation. XRD study confirmed the presence of both the lattice phases i.e. monoclinic and hexagonal wurtzite phase corresponding to α-Bi₂O₃ and ZnO in the α-Bi₂O₃-ZnO composite photocatalyst. FESEM images showed that α-Bi₂O₃-ZnO photocatalyst is composed of dumbbell like structures of ZnO with breadth ranging 4-5 μm and length ranging from 10 to 11 μm respectively. It was observed that α-Bi₂O₃ nanoparticles were attached on the ZnO surface and were in contact with each other. Low recombination rate of photo-induced electron-hole pairs, due to the migration of electrons and holes between the photocatalyst could be responsible for the 100% photocatalytic efficiency of α-Bi₂O₃-ZnO composite. In addition, photocatalyst was also observed to show the excellent antimicrobial activity with 1.5 cm zone of inhibition for 1 mg L^-1 dose, against the human pathogenic bacteria (S. aureus).

Computational modeling of ultraviolet light-emitting diode (UV-LED) reactor for water treatment

The ultraviolet light emitting diode (UV-LED) has recently emerged as a new UV source. It offers design flexibility due to its small size and ability to alter its radiation profile. In view of the variety of design possibilities for a UV-LED reactor, a computational model could be of great value for simulating the reactor and providing insight into its performance. Given the UV-LED's ability to emit various radiation wavelengths and because it is a directional UV source, the challenges of simulation for UV-LEDs are greater than those for UV lamps, which typically have a single wavelength and an almost radial radiation profile. This study proposes a method of simulating UV-LED reactors in the Eulerian framework through the integration of the kinetic, hydrodynamic, and radiation models, representing UV-LED systems. Additionally, the concept of an ideal UV-LED system is proposed, which can provide insight into the efficiency of any UV-LED reactor design concept. The integrated model of reactor performance is evaluated through experimental studies of challenge organisms (e.g., Escherichia coli and MS2) in two UV-LED reactors under different operating conditions, including flow rates, flow regimes, radiant powers, and UV-LED configurations. The close agreement between the numerical predictions and experimental data demonstrates the ability of the proposed method to simulate UV-LED reactor performance.

Investigation of Step-Stress Accelerated Degradation Test Strategy for Ultraviolet Light Emitting Diodes

III-nitride-based ultraviolet light emitting diode (UV LED) has numerous attractive applications in air and water purification, UV photolithography, and in situ activation of drugs through optical stimulus, solid state lighting, polymer curing, and laser surgery. However, the unclear failure mechanisms and uncertainty reliability have limited its application. Therefore, a design of an appropriate reliability test plan for UV LEDs has become extremely urgent. Compared to traditional reliability tests recommended in LED lighting industry, the step-stress accelerated degradation test (SSADT) is more cost-effective and time-effective. This paper compares three SSADT testing plans with temperature and driving currents as stepwise increasing loads to determine an appropriate test strategy for UV LEDs. The study shows that: (1) the failure mechanisms among different SSADT tests seem to be very different, since the driving current determines the failure mechanisms of UV LEDs more sensitively, and (2) the stepped temperature accelerated degradation test with an appropriate current is recommended for UV LEDs.

Moving from the traditional paradigm of pathogen inactivation to controlling antibiotic resistance in water - Role of ultraviolet irradiation

Ultraviolet (UV) irradiation has proven an effective tool for inactivating microorganisms in water. There is, however, a need to look at disinfection from a different perspective because microbial inactivation alone may not be sufficient to ensure the microbiological safety of the treated water since pathogenic genes may still be present, even after disinfection. Antibiotic resistance genes (ARGs) are of a particular concern since they enable microorganisms to become resistant to antibiotics. UV irradiation has been widely used for disinfection and more recently for destroying ARGs. While UV lamps remain the principal technology to achieve this objective, UV light emitting diodes (UV-LEDs) are novel sources of UV irradiation and have increasingly been reported in lab-scale investigations as a potential alternative. This review discusses the current state of the applications of UV technology for controlling antibiotic resistance during water and wastewater treatment. Since UV-LEDs possess several attractive advantages over conventional UV lamps, the impact of UV-LED characteristics (single vs combined wavelengths, and operational parameters such as periodic or pulsed and continuous irradiation, pulse repetition frequencies, duty cycle), type of organism, and fluence response, are critically reviewed with a view to highlighting the research needs for addressing future disinfection challenges. The energy efficiency of the reported UV processes is also evaluated with a focus on relating the findings to disinfection efficacy. The greater experience with UV lamps could be useful for investigating UV-LEDs for similar applications (i.e., antibiotic resistance control), and hence identification of future research directions.

Kinetic spectrophotometric method for real-time monitoring of ultraviolet photoreactions: A mini-photoreactor

It is proposed a new approach to evaluate the performance of ultraviolet photoreactions by integrating UV-LED and a UV-Vis cuvette as a mini-reactor for kinetic monitoring in a spectrophotometer not influenced by external light. This system uses only 3.0 mL of solutions in a rectangular quartz cuvette with a mini-bar magnetic stirrer in a cell holder and a UV-LED of 5 W with λ_max at 370 nm was positioned on the top of the cuvette and maintained at 25.0 ^oC. The effectiveness of this photoreactor was demonstrated by measuring the real-time degradation of two model compounds, salicylic acid and methylene blue, in homogeneous and heterogenous systems. Photolysis of MB with H₂O₂ results in increasing of rate constants as [H₂O₂] increased. Heterogeneous photocatalysis of MB and SA was fastest achieved in ZnO dosage of 0,20 g.L^-1. This mini-photoreactor allows monitoring the real-time kinetic performance collecting almost a thousand points in each experiment, leading to accurate rate constants. Moreover, this system presented positive environmental aspects such as: lower reactants and catalyst amounts, lower cost and waste amounts, use of the UV-LED radiation and labor time saving. This is a novel approach to determine the photoreaction effectiveness and it can be applied to systematic studies especially for the kinetic parameter determinations.

Effects of single and combined UV-LEDs on inactivation and subsequent reactivation of E. coli in water disinfection

Ultraviolet light emitting diodes (UV-LEDs) have shown a potential to replace traditional Ultraviolet (UV) pressure lamps for water disinfection. However, the research is not sufficient and hence, it is still difficult to make any logical conclusions. In this work, UV-LEDs with peak emissions at 267, 275, 310 nm and combined emissions at 267/275, 267/310 and 275/310 nm were applied to a batch water disinfection system. Under either single- or combined-wavelength situation, the inactivation efficiency, reactivation (due to photoreactivation and dark repair) after UV irradiation and electrical energy consumption were evaluated by way of the model bacterium Escherichia coli. It was found that, the 267 nm UV-LED had the highest inactivation efficiency than other UV-LEDs. Although reactivation occurred after 267, 275, 267/275 and 275/310 nm UV-LEDs' irradiations, it occurred to a lesser extent in dark repair than in photoreactivation, demonstrating that photo-effect is the dominant mechanism of reactivation. In addition, decay phase was more prominent than reactivation in dark repair. However, the irradiation by the 275 nm UV-LED showed a better persistence against reactivation which could be attributed to protein damage at 275 nm. No synergistic effect for combined wavelengths was observed in this study. The electrical energy consumption was lower for the 275 nm UV-LED than the other UV-LEDs which was attributed to its higher wall plug efficiency. This study showed the variation principle between the single and combined UVB/UVC-LEDs in inactivation efficiency, inhibition of reactivation, synergistic effect and electrical energy consumption in treatment of E. coli, which is useful for the reasonable exploitation of UV-LEDs in water disinfection systems.

Landfill leachate treatment by sequential combination of activated persulfate and Fenton oxidation

This work assesses the feasibility of sequential persulfate and Fenton oxidation for the decolorization and mineralization of landfill leachate (5600 mg L^-1 TOC; pH₀: 8.6) in a continuous batch-recirculation system. Firstly, it was analyzed the role of the operational conditions upon the persulfate activation evaluating the effects of electrolysis, ilmenite (FeTiO₃) as a source of Fe(II) and UV-LED (at 365 nm). The studied variables include current density (j) (50-200 mA cm^-2), persulfate dose (46.8-234 mM) and mineral concentration (500-1500 mg L^-1). The increase in j enhanced the hypochlorite generation and PS conversion to SO₄^- and, consequently, decolorization efficiency increasing the penetration of light through the solution and the photoreduction of Fe(III) to Fe(II) in the FeTiO₃ surface. The combined electrolysis/FeTiO₃/UV-LED showed synergetic effect compared to the individual processes, achieving mineralization around 53% under the optimum operating conditions (1 g L^-1 of FeTiO₃, using 234 mM of PS at 200 mA cm^-2 under UV-LED radiation). The subsequent Fenton oxidation once the pH decreased up to around 3, led to overall mineralization above 90% after 480 min, confirming the suitability of this combined treatment to deal with recalcitrant and highly colored effluents.

"Green" UV-LED gel nail polishes from bio-based materials

OBJECTIVE

Gel nail polishes represent an advanced class of nail polishes, with the ability to cure under ultraviolet (UV) radiation, and consequently demonstrate improved properties and greater durability compared to conventional nail polishes. Most gel nail polishes available today are based on petrochemical resources, making them unsustainable. Bio-based materials are excellent renewable resources, with high potential for meeting final-product performance, cost, and environmental needs. In addition, bio-based materials can be modified to make them amenable to being cured by advanced Light Emitting Diode (LED) resources that consume low energy and are safer for human exposure compared to conventional UV-mercury lamps. Consumer preference for use of products made from bio-based sources has been clearly growing. On the other hand, according to the U.S. Department of Energy (DOE) technology roadmap, a considerable amount of basic chemical building blocks should be derived from plant-based renewable materials in near future. However, to the best of our knowledge, bio-based nail products have not been sufficiently explored. Therefore, to keep pace with environmental regulations and consumer preference, there is an unmet opportunity to develop novel, sustainable nail gel polishes with considerable bio-renewable content. In this study, two sustainable UV-LED curable gel nail polish prototypes-one high-solids zero-volatile organic content (VOC) and the other waterborne, both with considerable bio-renewable content, were designed.

METHODS

Both formulations were cured under both UV-mercury and UV-LED radiation sources in order to evaluate their curing efficiency under a UV-LED source. Also, their performance was compared with a commercial petro-based benchmark.

RESULTS

The high-solids formulation demonstrated promising performance, exceeding that of the benchmark in opacity, chemical properties, gloss, and pendulum hardness, while the waterborne formulation met most of the desirable requirements with some significant technical benefits, including low odour and higher renewable raw material content.

CONCLUSION

These novel gel nail polishes are greener alternatives to the current products in the market with high potential for promising consumer acceptance.

Wavelength-dependent chlorine photolysis and subsequent radical production using UV-LEDs as light sources

UV-LEDs are considered as the most promising UV light sources, because it has the potential to replace conventional UV lamps in some water treatment applications in the foreseeable future. In this study, UV-LEDs at four wavelengths in the UV-C or near UV-C range (i.e., 257.7, 268, 282.3, and 301.2 nm) were used to investigate the wavelength-dependency on chlorine photolysis and its subsequent radical formation. The fluence-based photodecay rates of hypochlorous acid (HOCl) and hypochlorite (OCl^-) were monotonically correlated to their molar absorption coefficients and quantum yields, and the chlorine photodecay rates were much more significantly affected by molar absorption coefficients (β  = 0.949) than quantum yields (β  = 0.055). An empirical model that incorporated the chlorine photodecay rate constants, quantum yields, and molar absorption coefficients of HOCl and OCl^- was established, validated and then used to predict the chlorine photodecay rate at any wavelength (257.7-301.2 nm) and pH (5-10). The modelling results suggested that the maximum fluence-based rate constant (1.46 × 10^-4 m² J^-1) was obtained at 289.7 nm and pH 9.95. The wavelength dependency was larger at alkaline pH than at acidic pH, and the pH dependency was the largest at the longest wavelength. The formation of hydroxyl radicals (HO·) and reactive chlorine species (RCS) decreased with increasing wavelength at pH 6, and increased with increasing wavelength at pH 7. More HO· was formed at pH 6 than pH 7, but RCS showed the opposite pH-dependency. The findings in this study provide the fundamental information in selecting UV-LEDs with specific wavelength for enhancing/optimizing chlorine photodecay and/or its radical generation at different pHs in real-world applications.

Degradation mechanism of cyanide in water using a UV-LED/H2O2/Cu2+ system

In this study, we developed a UV-LED/H₂O₂/Cu²⁺ system to remove cyanide, which is typically present in metal electroplating wastewater. The results showed the synergistic effects of UV-LED, H₂O₂, and Cu²⁺ ions on cyanide removal in comparison with UV-LED photolysis, H₂O₂ oxidation, UV-LED/H₂O₂, and H₂O₂/Cu²⁺ systems. Cyanide was removed completely in 30 min in the UV-LED/H₂O₂/Cu²⁺ system, and its loss followed pseudo-first order kinetics. Statistically, both H₂O₂ and Cu²⁺ ions showed positive effects on cyanide removal, but Cu²⁺ ions exhibited a greater effect. The highest cyanide removal rate constant (k = 0.179 min^-1) was achieved at pH 11, but the lowest was achieved at pH 12.5 (k = 0.064 min^-1) due to the hydrolysis of H₂O₂ (pK_a of H₂O₂ = 11.75). The presence of dissolved organic matter (DOM) inhibited cyanide removal, and the removal rate constant exhibited a negative linear correlation with DOM (R² = 0.987). The removal rate of cyanide was enhanced by the addition of Zn²⁺ ions (from 0.179 to 0.457 min^-1), while the co-existence of Ni²⁺ or Cr⁺⁶ ion with Cu²⁺ ion reduced cyanide removal. The formation of OH radicals in the UV-LED/H₂O₂/Cu²⁺ system was verified using an aminophenyl fluorescence (APF) probe. Cyanate ions and ammonia were detected as the byproducts of cyanide decomposition. Finally, an acute toxicity reduction of 64.6% was achieved in the system within 1 h, despite a high initial cyanide concentration (100 mg/L). In terms of removal efficiency and toxicity reduction, the UV-LED/H₂O₂/Cu²⁺ system may be an alternative method of cyanide removal from wastewaters.

Understanding possible underlying mechanism in declining germicidal efficiency of UV-LED reactor

Since ultraviolet light emitting diodes (UV-LEDs) have emerged as an alternative light source for UV disinfection systems, enhancement of reactor performance is a demanding challenge to promote its practical application in water treatment process. This study explored the underlying mechanism of the inefficiency observed in flow-through mode UV disinfection tests to improve the light utilization of UV-LED applications. In particular, the disinfection performance of UV-LED reactors was evaluated using two different flow channel types, reservoir and pathway systems, in order to elucidate the impact of physical circumstances on germicidal efficiency as the light profile was adjusted. Overall, a significant reduction in germicidal efficiency was observed when exposure time was prolonged or a mixing chamber was integrated. Zeta analysis revealed that the repulsion rate between microorganisms decreased with UV fluence transfer, and that change might cause the shielding effect of UV delivery to target microorganisms. In line with the above findings, the reduction in efficiency intensified when opportunities for microbial collision increased. Thus, UV induced microbial aggregation was implicated as being a disinfection hindering factor, exerting its effect through uneven UV illumination. Ultimately, the results refuted the prevailing belief that UV has a cumulative effect. We found that the reservoir system achieved worse performance than the pathway system despite it providing 15 times higher UV fluence: the differences in germicidal efficiency were 1-log, 1.4-log and 1.7-log in the cases of P.aeruginosa, E.coli and S.aureus, respectively.

Comparison of UV-LED and low pressure UV for water disinfection: Photoreactivation and dark repair of Escherichia coli

Studies on ultraviolet light-emitting diode (UV-LED) water disinfection have shown advantages, such as safety, flexible design, and lower starting voltages. However, information about reactivation after UV-LED disinfection is limited, which is an important issue of UV light-based technology. In this study, the photoreactivation and dark repair of Escherichia coli after UV-LEDs and low pressure (LP) UV disinfection were compared. Four UV-LED units, 265 nm, 280 nm, the combination of 265 + 280 (50%), and 265 + 280 (75%) were tested. 265 nm LEDs was more effective than 280 nm LEDs and LP UV lamps for E. coli inactivation. No synergic effect for disinfection was observed from the combination of 265 and 280 nm LEDs. 265 nm LEDs had no different reactivation performances with that of LP UV, while 280 nm LEDs could significantly repress photoreactivation and dark repair at a low irradiation intensity of 6.9 mJ/cm². Furthermore, the UV-induced damage of 280 nm LEDs was less repaired which was determined by endonuclease sensitive site (ESS) assay. The impaired protein activities by 280 nm LEDs might be one of the reasons that inhibited reactivation. A new reactivation rate constant, K_max, was introduced into the logistic model to simulate the reactivation data, which showed positive relationship with the maximum survival ratio and was more reasonable to interpret the results of photoreactivation and dark repair. This study revealed the distinct roles of different UV lights in disinfection and reactivation, which is helpful for the future design of UV-LED equipment.

Photocatalytic decomposition of selected estrogens and their estrogenic activity by UV-LED irradiated TiO2 immobilized on porous titanium sheets via thermal-chemical oxidation

The removal of endocrine disrupting compounds (EDCs) remains a big challenge in water treatment. Risks associated with these compounds are not clearly defined and it is important that the water industry has additional options to increase the resiliency of water treatment systems. Titanium dioxide (TiO2) has potential applications for the removal of EDCs from water. TiO2 has been immobilized on supports using a variety of synthesis methods to increase its feasibility for water treatment. In this study, we immobilized TiO2 through the thermal-chemical oxidation of porous titania sheets. The efficiency of the material to degrade target EDCs under UV-LED irradiation was examined under a wide range of pH conditions. A yeast-estrogen screen assay was used to complement chemical analysis in assessing removal efficiency. All compounds but 17β-estradiol were degraded and followed a pseudo first-order kinetics at all pH conditions tested, with pH 4 and pH 11 showing the most and the least efficient treatments respectively. In addition, the total estrogenic activity was substantially reduced even with the inefficient degradation of 17β-estradiol. Additional studies will be required to optimize different treatment conditions, UV-LED configurations, and membrane fouling mitigation measures to make this technology a more viable option for water treatment.

Optical isopropanol biosensor using NADH-dependent secondary alcohol dehydrogenase (S-ADH)

Isopropanol (IPA) is an important solvent used in industrial activity often found in hospitals as antiseptic alcohol rub. Also, IPA may have the potential to be a biomarker of diabetic ketoacidosis. In this study, an optical biosensor using NADH-dependent secondary alcohol dehydrogenase (S-ADH) for IPA measurement was constructed and evaluated. An ultraviolet light emitting diode (UV-LED, λ=340nm) was employed as the excitation light to excite nicotinamide adenine dinucleotide (NADH). A photomultiplier tube (PMT) was connected to a two-way branch optical fiber for measuring the fluorescence emitted from the NADH. S-ADH was immobilized on the membrane to catalyze IPA to acetone and reduce NAD(+) to be NADH. This IPA biosensor shows highly sensitivity and selectivity, the calibration range is from 500 nmol L(-1) to 1mmolL(-1). The optimization of buffer pH, temperature, and the enzyme-immobilized method were also evaluated. The detection of IPA in nail related cosmetic using our IPA biosensor was also carried out. The results showed that large amounts of IPA were used in these kinds of cosmetics. This IPA biosensor comes with the advantages of rapid reaction, good reproducibility, and wide dynamic range, and is also expected to use for clinical IPA detections in serum or other medical and health related applications.

A new UV-LED device for automatic disinfection of stethoscope membranes

BACKGROUND

Stethoscopes are widely used by doctors and nurses. Poor stethoscope hygiene is a potential source of nosocomial infection. This study aimed to propose an innovative solution, based on the latest advances in ultraviolet (UV) light-emitting diodes (LEDs), for disinfecting stethoscope membranes automatically and efficiently.

METHODS

Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Enterococcus faecalis were sown on 28 stethoscope membranes and then transferred to Petri dishes. Treatment involved illuminating exposed Petri dishes with a UVC LED for 1 minute. For each microbe, the number of colony-forming units (cfu) at 36°C was compared in control and treated dishes using the Wilcoxon signed-rank test. The Kruskal-Wallis test was used to assess percent reductions in bacteria. Statistical significance was set at 99%.

RESULTS

A significant reduction in cfu counts after UV treatment (P < .01) was found for all bacteria: 85.5% for E faecalis, 87.5% for S aureus, 94.3% for E coli, and 94.9% for P aeruginosa . No significant differences in percent reduction in cfu were found between bacteria (P > .01).

CONCLUSION

The stethoscope, symbol of medicine and health care professionals, has been demonstrated to be a carrier of microorganisms. The treatment technique was effective and efficient in disinfecting the membranes. These promising results represent a step forward toward eliminating stethoscope membrane contamination with an innovative approach.

Optical fluence modelling for ultraviolet light emitting diode-based water treatment systems

This work presents a validated optical fluence rate model optimised for ultraviolet light-emitting diodes (UV-LEDs), which allow a very wide range of emission wavelengths and source geometries to be used in water treatment units. The model is based on a Monte Carlo approach, in which an incremental ray-tracing algorithm is used to calculate the local volumetric rate of energy absorption and subsequently convert it to the local fluence rate distribution for an UV-LED water treatment chamber of arbitrary design. The model includes contributions from optical reflections and scattering by treatment chamber walls and from scattering due to particulates and/or microorganisms. The model successfully predicts optical fluence rates in point-of-use water treatment units, as verified using biodosimetry with MS-2 bacteriophage at a UV-LED emission wavelength of 254 nm. The effects of chamber geometry are also modelled effectively and are consistent with the inactivation data for E. coli at 254 nm. The data indicate that this model is suitable for application in the design and optimisation of UV-LED-based water treatment systems.

Synthesis and characterization of Eu(III)-incorporated silica nanoparticles for application to UV-LED

A tetrakis(dibenzylmethanido) Eu(III) complex as a ultraviolet (UV) excited phosphor was synthesized, and incorporated with mesoporous silica as core-shell (CS), outer-shell (OS) and intermediate-shell (IS) architectures, using a combination of the self-organization process and the Stöber method. Exciting the Eu(III) complex at UV light produced a strong sensitized red-emission from Eu(III) by energy transfer from the ligand. Phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by casting the powdered complex and the incorporated silica nanoparticles onto a 365-nm InGaN chip, and their optical properties and thermal stability were investigated in terms of the chromaticity index and the intensity decay, respectively. The CS silica nanoparticle casted UV-LED exhibited the best perfomence with strong intensity and excellent thermal stability.

Fate of carbamazepine and anthracene in soils watered with UV-LED treated wastewaters

Water disinfection technologies based on ultraviolet (UV) radiations emitted by Light-Emitting Diodes (LED), as a wastewater tertiary treatment, have been shown to be promising for water reuse. Here, we assessed the fate of two ubiquitous pollutants, carbamazepine and anthracene, in soil watered with either UV-LED treated wastewaters or irrigation water. After 3 months, anthracene and carbamazepine were transformed two and three times faster respectively, in soils watered with UV-LED wastewater than in soils watered with tap water (probably because of the addition of organic matter by the effluent). Laccase activity was induced in the presence of the pollutants and anthraquinone was found as anthracene product of oxidation by laccases. Moreover, the addition of these pollutants into soil did not affect the functional diversity of autochthonous microbial communities assessed by Ecolog plates. Cellulase, protease and urease activities increased in soils watered with UV-LED treated wastewaters (UV-LED WW), showing transformation of organic matter from the effluent and lipase activity increased by anthracene addition, confirming the potential role of these enzymes as indicators of hydrocarbon contamination.