The development of ultraviolet light-emitting diodes (UV-LED) opens new possibilities for water treatment and photoreactor design. TiO
2
photocatalysis, a technology that has been continuously ...drawing attention, can potentially benefit from LEDs to become a sustainable alternative for the abatement of organic micropollutants (OMPs). Recently reported data on photocatalytic degradation of OMPs and their parameters of influence are here critically evaluated. The literature on OMP degradation in real water matrices, and at environmentally relevant concentrations, is largely missing, as well as the investigations of the impact of photoreactor design in pollutant degradation kinetics. The key factors for reducing UV-LED treatment technology costs are pointed out, like the increase in external quantum and wall-plug efficiencies of UV-LEDs compared to other technologies, as well as the need for an appropriate design optimizing light homogeneity in the reactor. Controlled periodic illumination, wavelength coupling and H
2
O
2
addition are presented as efficiency enhancement options. Although electrical energy per order (
E
EO
) values for UV-LED photocatalysis have decreased to the range of traditional mercury lamps, values are still not low enough for practical employment. Moreover, due to the adoption of high initial OMP concentration in most experiments, it is likely that most literature
E
EO
values are overestimated. Given the process characteristics, which are favoured by translucent matrices and small diameters for more homogenous light distribution and better transportation of radicals, innovative reactor designs should explore the potential of point-of-use applications to increase photocatalysis applicability at large scale.
Recent developments in UV-LED technology open up new possibilities for water treatment. TiO2 photocatalysis can benefit from optimized photoreactor design to increase hydroxyl radical production and ...reduce its electrical energy per order (EEO) demands, which still ranks high among advanced oxidation processes. However, literature on UV-LED photoreactor design is largely lacking. In this work, a detailed investigation of photoreactor design is proposed. The simulation of a lab scale cylindrical reactor with 8 different UV-LED arrays was run with the professional version of an optic software. The increase of radiant flux and irradiance on the reactor’s middle cross section and side walls, respectively, was related to an increasing number of LEDs and to a shorter distance from the reactor but not necessarily to an increase in homogeneity of light distribution. A full factorial experimental design was applied to evaluate the degradation of a representative contaminant of emerging concern (ciprofloxacin) considering 4 independent variables and their interactive effects on kinetic rates and EEO values. The significance of these effects was evaluated with ANOVA and a prediction model was established. The results show that the presence of a TiO2 nanofilm was the most significant tested effect. The number of LEDs, their distance from the reactor’s wall and the adoption of controlled periodic illumination also greatly influenced kinetic rates but were less relevant for reducing EEO values because the energetic trade-off was not sufficient to turn the kinetic gain into lower electricity demands.
Ultra-violet light-emitting diode (UV-LED)-based processes for water treatment have shown the potential to surpass the hurdles that prevent the adoption of photocatalysis at a large scale due to ...UV-LEDs’ unique features and design flexibility. In this work, the degradation of five EU Watch List 2020/1161 pharmaceutical compounds was comprehensively investigated. Initially, the UV-A and UV-C photolytic and photocatalytic degradation of individual compounds and their mixtures were explored. A design of experiments (DoE) approach was used to quantify the effects of numerous variables on the compounds’ degradation rate constant, total organic carbon abatement, and toxicity. The reaction mechanisms of UV-A photocatalysis were investigated by adding different radical scavengers to the mix. The influence of the initial pH was tested and a second DoE helped evaluate the impact of matrix constituents on degradation rates during UV-A photocatalysis. The results showed that each compound had widely different responses to each treatment/scenario, meaning that the optimized design will depend on matrix composition, target pollutant reactivity, and required effluent standards. Each situation should be analyzed individually with care. The levels of the electrical energy per order are still unfeasible for practical applications, but LEDs of lower wavelengths (UV-C) are now approaching UV-A performance levels.
Abstract
Contaminants of emerging concern (CECs) and their respective transformation products (TPs) formed following photodegradation pose considerable threats to the environment and our health. The ...formation of TPs during UV-LED-based degradation of three target pollutants in the EU Watch List of CECs was accessed by LC-MS-Orbitrap, and their reaction pathways were elucidated. The influence of different matrices and treatments of choice on TP formation was investigated. Results showed that matrix changes did not produce different reaction pathways during UV-A photocatalysis, although plots of TP peak areas vs. time were different for each case. A new TP was found for the antidepressant venlafaxine, (1-2-(dimethylnitroryl)-1-(4-methoxyphenyl)ethylcyclohexanol. When comparing UV-A photocatalysis with UV-C photolysis, dissimilar pathways were observed due to the distinct reaction mechanisms of each process, since photocatalysis, unlike photolysis, relies on radical-based reaction routes. Different levels of confidence were obtained for each TP depending on the availability of MS2 data in the literature and of standards for comparison. All the found TPs had similar molecular masses in comparison to their respective parent compounds. Most of the TPs remained in the effluent after 6 hours of photodegradation, which highlights the importance of their control, close-monitoring, and further toxicity assessments.
The development of ultraviolet light-emitting diodes (UV-LED) opens new possibilities for water treatment and photoreactor design. TiO
photocatalysis, a technology that has been continuously drawing ...attention, can potentially benefit from LEDs to become a sustainable alternative for the abatement of organic micropollutants (OMPs). Recently reported data on photocatalytic degradation of OMPs and their parameters of influence are here critically evaluated. The literature on OMP degradation in real water matrices, and at environmentally relevant concentrations, is largely missing, as well as the investigations of the impact of photoreactor design in pollutant degradation kinetics. The key factors for reducing UV-LED treatment technology costs are pointed out, like the increase in external quantum and wall-plug efficiencies of UV-LEDs compared to other technologies, as well as the need for an appropriate design optimizing light homogeneity in the reactor. Controlled periodic illumination, wavelength coupling and H
O
addition are presented as efficiency enhancement options. Although electrical energy per order (E
) values for UV-LED photocatalysis have decreased to the range of traditional mercury lamps, values are still not low enough for practical employment. Moreover, due to the adoption of high initial OMP concentration in most experiments, it is likely that most literature E
values are overestimated. Given the process characteristics, which are favoured by translucent matrices and small diameters for more homogenous light distribution and better transportation of radicals, innovative reactor designs should explore the potential of point-of-use applications to increase photocatalysis applicability at large scale.
Ultra-violet light-emitting diode (UV-LED)-based processes for water treatment have shown the potential to surpass the hurdles that prevent the adoption of photocatalysis at a large scale due to ...UV-LEDs' unique features and design flexibility. In this work, the degradation of five EU Watch List 2020/1161 pharmaceutical compounds was comprehensively investigated. Initially, the UV-A and UV-C photolytic and photocatalytic degradation of individual compounds and their mixtures were explored. A design of experiments (DoE) approach was used to quantify the effects of numerous variables on the compounds' degradation rate constant, total organic carbon abatement, and toxicity. The reaction mechanisms of UV-A photocatalysis were investigated by adding different radical scavengers to the mix. The influence of the initial pH was tested and a second DoE helped evaluate the impact of matrix constituents on degradation rates during UV-A photocatalysis. The results showed that each compound had widely different responses to each treatment/scenario, meaning that the optimized design will depend on matrix composition, target pollutant reactivity, and required effluent standards. Each situation should be analyzed individually with care. The levels of the electrical energy per order are still unfeasible for practical applications, but LEDs of lower wavelengths (UV-C) are now approaching UV-A performance levels.
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