Examinando por Autor "Pablos, Cristina"

Mostrando 1 - 20 de 22

A review on LED technology in water photodisinfection
(Elsevier, 2023) Martín-Sómer, Miguel; Pablos, Cristina; Adán, Cristina; Grieken, Rafael van; Marugán, Javier
The increase in efficiency achieved by UV LED devices has led to a compelling increase in research reports on UV LED water treatment for consumption in the past few years. This paper presents an in-depth review based on recent studies on the suitability and performance of UV LED-driven processes for water disinfection. The effect of different UV wavelengths and their combinations was analysed for the inactivation of various microorganisms and the inhibition of repair mechanisms. Whereas 265 nm UVC LED present a higher DNA damaging potential, 280 nm radiation is reported to repress photoreactivation and dark repair. No synergistic effects have been proved to exist when coupling UVB + UVC whereas sequential UVA-UVC radiation seemed to enhance inactivation. Benefits of pulsed over continuous radiation in terms of germicidal effects and energy consumption were also analysed, but with inconclusive results. However, pulsed radiation may be promising for improving thermal management. As a challenge, the use of UV LED sources introduces significant inhomogeneities in the light distribution, pushing for the development of adequate simulation methods to ensure that the minimum target dose required for the target microbes is achieved. Concerning energy consumption, selecting the optimal wavelength of the UV LED needs a compromise between the quantum efficiency of the process and the electricity-to-photon conversion. The expected development of the UV LED industry in the next few years points to UVC LED as a promising technology for water disinfection at a large scale that could be competitive in the market in the near future.
Analogies and differences between photocatalytic oxidation of chemicals and photocatalytic inactivation of microorganisms
(ELSEVIER, 2010) Marugán, Javier; van Grieken, Rafael; Pablos, Cristina; Sordo, Carlos
This study reports the analogies and differences found when comparing TiO2 photocatalytic treatment for chemical oxidation and microorganisms inactivation, using methylene blue and Escherichia coli as references, respectively. In both processes the activation is based on the same physicochemical phenomena and consequently a good correlation between them is observed when analyzing the effect of operational variables such as catalyst concentration or incident radiation flux, both factors influencing common stages such radiation absorption and generation of reactive oxygen species. However, different microbiological aspects (osmotic stress, repairing mechanism, regrowth, bacterial adhesion to the titania surface, etc) makes disinfection kinetics significantly more complex than the first-order profiles usually observed for the oxidation of chemical pollutants. Moreover, bacterial inactivation reactions are found to be extremely sensitive to the composition of water and modifications of the catalysts in comparison with the decolorization of the dye solutions, showing opposite behaviors to the presence of chlorides, incorporation of silver to the catalysts or the use of different types of immobilized TiO2 systems. Therefore, the activity observed for the photocatalytic oxidation of organics can not be always extrapolated to photocatalytic disinfection processes.
Comparative evaluation of acute toxicity by Vibrio fischeri and fern spore based bioassays in the follow-up of toxic chemicals degradation by photocatalysis
(ELSEVIER, 2012) Marugán, Javier; Bru, David; Pablos, Cristina; Catalá, Myriam
The development of efficient bioassays is a necessary step for cost-effective environmental monitoring and evaluation of novel decontamination technologies. Marine Vibrio fischeri kits have demonstrated to be extremely sensitive but lack of ecological relevance, especially when assessing impacts on freshwater higher organisms. A novel riparian fern spore microbioassay could merge higher ecological relevance and reduced costs. The aim of this work is the comparative evaluation of the Vibrio fischeri and fern spore bioassays for the follow up of detoxification processes of 30 water contaminated with cyanide and phenol by advanced oxidation technologies, using heterogeneous photocatalysis as example. In both cases, EC50 values differed significantly for V.fisheri commercial kit, V.fisheri lab cultures and Polystichum setiferum fern spores (1.9, 16 and 101 mg cyanide L-1 and 27.0, 49.3 and 1440 mg phenol L-1, respectively). Whereas V.fischeri bioassays are extremely sensitive and dilution series must be prepared, toxicant solutions can be directly applied to spores. Spore microbioassay was also useful in the follow up of photoxidation processes of cyanide and phenol, also reflecting the formation of intermediate degradation by-products even more toxic than phenol. We conclude that this new microbioassay is a promising cost-effective tool for the follow up of decontamination processes.
Comparison between the Photocatalytic inactivation of Gram-positive E. Faecalis and Gram-negative E. Coli Faecal contamination indicator microorganism
(ELSEVIER, 2010) van Grieken, Rafael; Marugán, Javier; Pablos, Cristina; Furones, Laura; López, Ainhoa
Photocatalytic inactivation of two different faecal contamination indicator microorganisms, the Gram-negative Escherichia coli and the Gram-positive Enterococcus faecalis, has been studied using TiO2 in suspension and immobilized onto the photocatalytic reactor wall. The effect of the main variables of the photocatalytic process on the disinfection efficiency in deionized water and simulated effluent of wastewater treatment plant (WTP) effluents has been analyzed. Noticeable differences were observed between both types of bacteria during photolytic experiments without TiO2 in deionized water, probably due to the higher sensibility of E. coli to the osmotic stress, which leads to a higher cell membrane permeability and consequently a lower amount of hydroxyl radical attacks required to overcome the inactivation threshold. In contrast, despite their structural differences, Gram-positive and Gram-negative bacteria seem to follow the same inactivation mechanism, showing no significant differences in the experiments carried out with TiO2 in suspension either in deionized water or in WTP simulated effluent, and similar responses to changes in the concentration of catalysts and irradiation power (both variables involved in the hydroxyl radical generation). Similar results are observed using immobilized TiO2 in deionized water. However, disinfection experiments of WTP simulated effluent using immobilized TiO2 showed much longer initial delays before the beginning of the inactivation for E. faecalis, suggesting a critical effect of the water composition of the bacteria-catalyst interaction. In any case, the irradiation time required to achieved the inactivation below the experimental bacterial detection limit is similar for both microorganisms, and experiments with mixtures of E.faecalis and E.coli in WTP simulated effluent show no significant differences. Therefore, it can be concluded that the results of photocatalytic disinfection experiments using E. coli as model bacteria could be reasonably extrapolated to other types of bacteria or bacterial mixtures.
Comparison of the photocatalytic disinfection of E.COLI suspensions in slurry, wall and fixed-bed reactors
(ELSEVIER, 2009) van Grieken, Rafael; Marugan, Javier; Sordo, Carlos; Pablos, Cristina
The performances of different configurations of photoreactors were compared for the photocatalytic disinfection of E. coli aqueous suspensions and methylene blue photodegradation. Titania was immobilized in an annular reactor in two different ways: on the inner reactor wall and on the packing of a fixed bed. The influence of the increase in the TiO2 layer thickness has been studied, and the results have been compared with those obtained with TiO2 slurries of increasing concentration. Experimental results for methylene blue degradation were in agreement with those expected from the characterization data of the immobilized systems, but they did not fit with the variation of the activity for microorganisms inactivation. The increase in the density of the TiO2 film caused by the heat treatment carried out after every coating cycle reduce the TiO2 surface available for the interaction with bacteria, although it remains accessible for the dye molecules. Although immobilized systems show a lower disinfection activity in deionized water than TiO2 slurries, they show a lower inhibition by the presence of organic matter, leading to comparable irradiation times to reach bacterial concentrations below the detection limit in the treatment of wastewater treatment plant effluents. Moreover, immobilized systems have shown that they are stable and do not present deactivation after several cycles of reuse, being readily applicable for continuous water treatment systems.
Correlation between photoelectrochemical behaviour and photoelectrocatalytic activity and scaling-up of P25-TiO2 electrodes
(Elsevier, 2014) Pablos, Cristina; Marugán, Javier; Grieken, Rafael van; Adán, Cristina; Riquelme, Ainhoa; Palma, Jesús
The use of TiO2 electrodes may solve the two main drawbacks of photocatalytic processes: i) the necessity of recovering the catalyst and ii) the low quantum yield in the use of the radiation. This work focuses on the correlation between the photoelectrochemical properties of TiO2 electrodes and their activity for the photoelectrocatalytic oxidation of methanol. Particulate TiO2 electrodes prepared by deposition of P25-TiO2 nanoparticles on titanium (TiO2/Ti) or conductive glass support (TiO2/ITO) seem to be effective for charge carrier transference on TiO2 surface favouring the formation of ¿OH radicals and consequently, the oxidation of molecules. In contrast, thermal TiO2 electrodes prepared by annealing of titanium (Ti) present better properties for charge carrier separation as a consequence of the application of a potential bias. Despite reducing charge carrier recombination by applying an electric potential bias, the activity of thermal electrodes remains lower than that of P25-particulate electrodes. TiO2 structure of P25-particulate electrodes does not completely allow developing a potential gradient. However, their adequate TiO2 layer characteristics for charge carrier transfer lead to a reduction in charge carrier recombination making up for the lack of charge carrier separation when applying an electric potential bias. TiO2/Ti showed the highest values of activity. Therefore, the combination of the suitable TiO2 surface properties for charge carrier transfer with an adequate conductive support seems to increase the properties of the electrode for allowing charge carrier separation. The scaling-up calculations for a TiO2/ITO electrode do lead to good estimations of the activity and photocurrent of larger electrodes since this photoanode made from ITO as conductive support does not seem to be significantly affected by the applied potential bias.
Critical assessment of optical sensor parameters for the measurement of ultraviolet LED lamps
(Elsevier, 2022) Uppinakudru, Adithya Pai; Reynolds, Ken; Stanley, Simon; Pablos, Cristina; Marugán, Javier
Measurement of light output from ultraviolet (UV) light-based devices is critical to understanding the capability of the device. Optical sensors such as radiometers and dosimeters can possess different angular responses and are sensitive to many parameters in the measurement set-up. This work has been designed to quantify the effect of multiple parameters on the measurements obtained from optical sensors to provide inputs for validating measured data for ultraviolet sources. Multiple light sources operating in the ultraviolet range have been measured and a comparison between different sensors is presented. The angular response has been evaluated for each detector and compared with an ideal cosine response. Two of the six sensors studied displayed a near cosine response. A change of angle of acceptance with wavelength was observed for the ThorLabs S120VC and ILT W Optic diffuser. Due to use of artificial heating, the effect of measured intensities on the sensor as a function of temperature was seen to be insignificant but provided an understanding of how temperature of the sensor can influence measured data. Finally, the effect of ambient light and the integration time on the measured data were investigated. The effect of ambient light proved to be significant, when not considered in measurement of low light signals sources while the effect of choosing an ideal integration time has been seen to impact the measurements obtained. A measured difference of 43% was observed between a saturated and unsaturated sensor.
Critical review of technologies for the on-site treatment of hospital wastewater: From conventional to combined advanced processes
(Elsevier, 2022) Pariente, María Isabel; Segura, Yolanda; Alvarez, Silvia; Casas, J.A.; Pedro, Z.M. de; Diaz, E.; García, J.; López-Muñoz, M.J.; Marugán, Javier; Mohedano, Ángel Fernandez; Molina, Raúl; Muñoz, M.; Pablos, Cristina; Perdigón-Melón, J.A.; Petre, A.L.; Rodríguez, J.J.; Tobajas, M.; Martínez, F.
This review aims to assess different technologies for the on-site treatment of hospital wastewater (HWW) to remove pharmaceutical compounds (PhCs) as sustances of emerging concern at a bench, pilot, and full scales from 2014 to 2020. Moreover, a rough characterisation of hospital effluents is presented. The main detected PhCs are antibiotics and psychiatric drugs, with concentrations up to 1.1 mg/L. On the one hand, regarding the presented technologies, membrane bioreactors (MBRs) are a good alternative for treating HWW with PhCs removal values higher than 80% in removing analgesics, anti-inflammatories, cardiovascular drugs, and some antibiotics. Moreover, this system has been scaled up to the pilot plant scale. However, some target compounds are still present in the treated effluent, such as psychiatric and contrast media drugs and recalcitrant antibiotics (erythromycin and sulfamethoxazole). On the other hand, ozonation effectively removes antibiotics found in the HWW (>93%), and some studies are carried out at the pilot plant scale. Even though, some families, such as the X-ray contrast media, are recalcitrant to ozone. Other advanced oxidation processes (AOPs), such as Fenton-like or UV treatments, seem very effective for removing pharmaceuticals, Antibiotic Resistance Bacteria (ARBs) and Antibiotic Resistance Genes (ARGs). However, they are not implanted at pilot plant or full scale as they usually consider extra reactants such as ozone, iron, or UV-light, making the scale-up of the processes a challenging task to treat high-loading wastewater. Thus, several examples of biological wastewater treatment methods combined with AOPs have been proposed as the better strategy to treat HWW with high removal of PhCs (generally over 98%) and ARGs/ARBs (below the detection limit) and lower spending on reactants. However, it still requires further development and optimisation of the integrated processes.
Emerging micropollutant oxidation during disinfection processes using UV-C, UC-C/H2O2, UV-A/TiO2 and UV-A/TiO2/H2O2
(Elsevier, 2013) Marugán, Javier; Pablos, Cristina; Grieken, Rafael van; Serrano, Elena
Regeneration of wastewater treatment plant effluents constitutes a solution to increase the availability of water resources in arid regions. Water reuse legislation imposes an exhaustive control of the microbiological quality of water in the operation of disinfection tertiary treatments. Additionally, recent reports have paid increasing attention on emerging micropollutants with potential biological effects even at trace level concentration. This work focuses on the evaluation of several photochemical technologies as disinfection processes with the aim of simultaneously achieving bacterial inactivation and oxidation of pharmaceuticals as examples of emerging micropollutants typically present in water and widely studied in the literature. UV-C-based processes show a high efficiency to inactivate bacteria. However, the bacterial damages are reversible and only when using H2O2, bacteria reproduction is affected. Moreover, a complete elimination of pharmaceutical compounds was not achieved at the end of the inactivation process. In contrast, UV-A/TiO2 required a longer irradiation time to inactivate bacteria but pharmaceuticals were completely removed along the process. In addition, its oxidation mechanism, based on hydroxyl radicals (¿OH), leads to irreversible bacterial damages, not requiring of chemicals to avoid bacteria regrowth. For UV-A/TiO2/H2O2 process, the addition of H2O2 improved E. coli inactivation since the cell wall weakening, due to ¿OH attacks, allowed H2O2 to diffuse into the bacteria. However, a total elimination of the pharmaceuticals was not achieved during the inactivation process.
Environmental life cycle assessment of UV-C LEDs vs. mercury lamps and oxidant selection for diclofenac degradation
(Elsevier, 2024) Pizzichetti, Raffaella; Martín-Gamboa, Mario; Pablos, Cristina; Reynolds, Ken; Stanley, Simon; Dufour, Javier; Marugán, Javier
This study is the first environmental comparison between a UV-C LED lamp (emitting at 265 nm) and mercury lamps employed in a lab-scale photoreactor for water treatment purification purposes, using the removal of diclofenac as a case study. Ex-ante life cycle assessment (LCA) methodology was used as a robust method to identify hotspots and recommendations at the early stage of the UV-C LEDs technology. The functional unit was defined as “the treatment of 1 L of polluted water with 20 mg L−1 of diclofenac to achieve a 90% removal of the contaminant”, while the system boundaries include the production and the operation of the photoreactors, following a cradle-to-gate approach. Several scenarios were explored, and overall, the UV-C LED lamp shows a promising environmental performance, with less or similar potential impacts than the mercury lamps in the 16 categories selected from the Environmental Footprint (EF) method. In particular, it reveals less impact in “human toxicity non-cancer” and “resource use minerals and metals” and presents electricity as the main source of impact. Given the higher efficacy of the UV-driven advanced oxidation processes compared to the UV irradiation alone, and since no studies have previously been conducted on the sustainability of free chlorine (FC) as an oxidant in water treatment, a comparison between UV-C, UV-C/H2O2, and UV-C/FC while employing the 265 nm UV-C LED lamp was also assessed. UV-C/H2O2 was more sustainable than UV-C/FC for the same treatment time, but both led to an overall impact reduction of 35% and 30%, respectively. To increase sustainability, employing cleaner energy sources such as photovoltaic or wind energy also resulted in an 80% and 93% reduction in the “climate change” category. Overall, this study demonstrates that using UV-C LEDs and the selected oxidants for water purification is beneficial and encourages the scale-up of the system.
Evaluation of the uniformity of UVA LED illumination on flat surfaces: Discrete ordinate method, single axis, and surface scanning radiometry
(Elsevier, 2023) Reddick, Conor; Casado, Cintia; Reynolds, Ken; Stanley, Simon; Pablos, Cristina; Marugán, Javier
Uniform illumination from UVA LED lamps is a crucial design characteristic for a range of industries including photocatalytic applications. In this work, radiometry and the discrete ordinate method (DOM) are used to determine the ideal target surface size and working distance from a UVA LED lamp for highly uniform illumination. Horizontal incident radiation and full surface incident radiation measurements were conducted using a scanning radiometry technique. It is shown that horizontal incident and full surface incident radiation measurements show good agreement for uniformity measurements over a range of working distances, with maximum uniformity (2.6% and 3.6% standard deviation respectively) over the measured range found at 15 mm working distance. DOM simulation results showed good agreement with radiometry for power and incident radiation measurements, whilst indicating a maximum uniformity at 20 mm working distance. These results demonstrate that DOM simulations can be used as a fast, low cost, and reliable indication of surface uniformity, peak surface irradiance, and power measurements in the design of UV lamps for industrial and academic applications.
Growth and prevalence of antibiotic-resistant bacteria in microplastic biofilm from wastewater treatment plant effluents
(Elsevier, 2022) Perveen, Shabila; Pablos, Cristina; Reynolds, Ken; Stanley, Simon; Marugán, Javier
It is accepted that Microplastic (MP) biofilms accumulates antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) in water. ARB/ARGs and MPs are emerging pollutants of concern due to various associated health risks. The objective of this study was to 1) investigate the ARB community in a pilot-scale wastewater treatment plant (WWTP) effluent, 2) to study and visualize the ARB/ARGs in MP biofilm grown in WWTP effluent and tap water, and 3) to analyze microplastic adherent ARB/ARGs in the biofilm and planktonic ARB/ARGs in the filtrate under controlled conditions. Results indicated the dominance of Pseudomonas, Aeromonas, and Bacillus among isolated ARB in WWTP effluent. Representative resistance strains were incubated in 300 mL water containing commercial polystyrene beads of 300550 μm diameter (MP) in a series of batch experiments. Microbiological, molecular, and microscopic analyses were performed by enumeration, 16srRNA, real-time polymerase chain reaction (qPCR), and Field Emission-Scanning Electron Microscopy (FEG-SEM) techniques. The analyzed viable ARB indicated an increasing trend in MP biofilms between days 3 and 5. It further decreased on days 7 and 9. The prevalence of ARB in the filtrate and MP biofilm varied as a function of time and TOC level, while no significant impacts were observed for minor temperature variation, low antibiotic pressure, and increased MP mass with few exceptions. Relative abundance of ARGs (vanA, sul1) and integron integrase gene (intl1) in MP biofilm were significantly different across different TOC levels, time, and antibiotic pressure. ARGs and intl1 were detected in the MP biofilm in tap water and WWTP effluent on day 30.
Kinetic and mechanistic analysis of membrane fouling in microplastics removal from water by dead-end microfiltration
(Elsevier, 2023) Pizzichetti, A. Raffaella P.; Pablos, Cristina; Álvarez-Fernández, Carmen; Reynolds, Ken; Stanley, Simon; Marugán, Javier
This study explores and analyses the kinetic and mechanistic aspects of microfiltration cellulose acetate membrane fouling by polyamide (PA) and polystyrene (PS) particles in dead-end configuration and the main interactions between the microplastics and the membrane during the filtration process. First, PA and PS particles were characterised to define the differences in shape (regular and irregular), particle size distribution (10–105 µm and 20–320 µm), and surface charge (neutral and negative). The results showed that the prevailing mechanisms during microplastic filtrations were complete pore blocking followed by cake layer formation in both cases. The mechanisms’ kinetics were positively correlated to MPs load through a power-law relationship which was stronger for PS than for PA particles because of higher steric hindrance effects. On the other hand, increasing the working transmembrane pressure led to an optimum working condition, between 0.3 and 0.5 bar for PA and 0.3 bar for PS filtration. Overall, higher fouling was induced by the PA particles due to the higher PA hydrophobicity and their smaller size, which caused a denser cake layer. Instead, PS particles with higher irregularities and repulsive electrostatic forces formed a more porous layer but induced a high degree of abrasion on the membrane surface. Finally, membrane fouling led to an increase in hydrophobicity and roughness, probably causing further fouling. To conclude, modelling membrane fouling can help predict the best working conditions and the membrane replacement cycles to increase the MPs removal efficiency and reduce secondary MP-based pollution.
Kinetic modelling of Escherichia coli inactivation in a photocatalytic wall reactor
(Elsevier, 2014) Marugán, Javier; Grieken, Rafael van; Pablos, Cristina; Satuf, M. Lucila; Cassano, Alberto E.; Alfano, Orlando M.
A kinetic model of the photocatalytic inactivation of Escherichia coli in an annular wall reactor is presented. The model is based on a reaction scheme that involves a series of events in which bacteria are progressively damaged and eventually led to cell lysis. The model explicitly takes into account radiation absorption effects. Photocatalytic inactivation experiments were carried out in a photoreactor operated in a closed recirculating circuit with a reservoir tank and irradiated with a 6W black light lamp situated in the axis of the reactor. Immobilization of TiO2 Aeroxide P25 has been carried out by the dip-coating procedure onto the inner-tube wall of the annular reactor. Experimental results for different TiO2 layer thicknesses were used to estimate the kinetic parameters of the model. Good agreement between model predictions and inactivation experiments was achieved in the whole range of TiO2 thicknesses studied.
Novel procedure for the numerical simulation of solar water disinfection processes in flow reactors
(Elsevier, 2018) García-Gil, Ángela; Casado, Cintia; Pablos, Cristina; Marugán, Javier
A novel procedure for the simulation of solar water disinfection (SODIS) processes in flow reactors is presented. The modeling approach includes the rigorous description of hydrodynamics, radiation transfer, mass transport and bacterial inactivation phenomena within the reactor by means of a computational fluid dynamics (CFD) software. The methodology has been evaluated in a tubular reactor coupled with a compound parabolic collector (CPC). Velocity profiles have been validated versus theoretical fully developed flow, and radiation fields versus both ray tracing and experimental actinometrical measurements. Incorporation of the solar vector calculation significantly improves the model capabilities for prediction of the potential performance of the SODIS process at different geographical coordinates and operation time. A mechanistic kinetic model was used for the description of the bacterial inactivation rate with explicit radiation absorption effects, coupling the radiation field with the mass balances of viable bacterial species. Model predictions successfully reproduce the experimental data of E. coli inactivation under different irradiances of both simulated and natural solar light with a normalized root mean squared logarithmic error (NRMSLE) of 6.65% and 9.72%, respectively. Therefore, this novel methodology is confirmed as a useful tool for the scaling-up of the SODIS process to large volume systems to be installed in remote communities where safe drinking water is not available.
Photocatalytic inactivation of bacteria in a fixed-bed reactor: mechanistic insights by epifluorescence microscopy
(ELSEVIER, 2011) Pablos, Cristina; van Grieken, Rafael; Marugán, Javier; Moreno, Beatriz
The photocatalytic inactivation of Escherichia coli bacteria with titanium dioxide immobilised in a fixed-bed reactor has been studied and compared with the results obtained using aqueous titania suspensions. In both cases, the photocatalytic inactivation has been successfully achieved, reaching a 6-log decrease in the concentration of bacteria. The slurry system shows a higher inactivation rate at the beginning of the reaction that decreases progressively, whereas the fixed-bed reactor increases the inactivation rate as the irradiation time increases, leading both catalytic systems to comparable irradiation times for the total inactivation of bacteria, i.e. concentration below the detection limit. This opposite trend seems to be related to differences in the bacteria-TiO2 interaction, being also observed that the fixed-bed catalytic system is less affected by the competition for the oxidant species of byproducts released after the bacterial cell lysis. Epifluorescence microscopy pictures taken after a dual DAPI/PI staining membrane permeability assay provide mechanistic insights into this different behaviour, showing for the fixed-bed experiments an increase in the damaged bacteria from the very beginning of the reaction, whereas for the slurry system they were not observed until longer irradiation exposition is achieved. These results suggest as hypothesis that although in absolute terms the number of hydroxyl radical attacks could be even lower in the immobilised systems, the damages are more concentrated on the area in which the bacteria-TiO2 interaction takes place. Although the fixed-bed reactor requires comparable irradiation time for total inactivation of bacteria than that corresponding to the slurry system, it shows minor deactivation and allows the continuous operation without the need of particles removal, making this immobilised system a good alternative to successfully scale-up the photocatalytic disinfection technology.
Photocatalytic inactivation of bacteria in water using suspended and immobilized silver TiO2
(ELSEVIER, 2009) van Grieken, Rafael; Marugan, Javier; Sordo, Carlos; Martinez, Patricia; Pablos, Cristina
Incorporation of silver to titanium dioxide is of great interest for photocatalytic disinfection applications since in addition to the enhancement of the electron-hole separation and interfacial charge transfer and the increase in the visible light response, silver compounds present a strong bactericidal effect. Ag/TiO2 materials used in suspension and immobilized in two different configurations (catalytic wall and fixed-bed reactors) have been prepared, characterized and tested using Escherichia coli as model microorganism. Although the incorporation of silver to powdered Degussa P25 TiO2 increases the activity, the thermal treatment required for the stabilization of the supported metal particles reduces the global efficiency. The comparison with experiments of dye photodegradation indicates that the activity of Ag/TiO2 is mainly due to the bactericidal role of silver and not to the enhancement of the photocatalytic mechanism. The best tested system has been proved to be the Ag/TiO2 catalytic wall reactor with a 0.6 wt% of Ag loading, showing a high activity both in relative (per gram of TiO2) and absolute terms, an optimal use of the radiation source, and a good stability of the film with negligible silver lixiviation, allowing the continuous treatment of water.
Photoelectrochemical disinfection efficiency of WO3-based photoanodes: Development of multifunctional photoelectrocatalytic materials
(Elsevier, 2024-07) Reddick, Connor; Sotelo-Vázquez, Carlos; Tam, Brian; Reynolds, Ken; Stanley, Simon; Creasey, George; Hankin, Anna; Pablos, Cristina; Marugán, Javier
Access to safe water is a growing global concern, with millions lacking acceptable water sources. Photocatalysis offers eco-friendly water remediation, yet its combination with electrocatalysis for both water treatment and hydrogen production remain underexplored. This study investigates UVA LED photoelectrocatalysis using WO3-based photoanodes, alone or in heterojunction with BiVO4, to purify wastewater and co-produce hydrogen. Tests on polluted water streams containing 105 PFU mL−1 of MS2 bacteriophage virus and 106 CFU mL−1 of E. coli reveal that nanostructured WO3 achieves rapid MS2 disinfection within 5 min. (k= 0.80 min−1), with enhanced efficiency over flat counterparts. However, nanostructuring does not improve E. coli inactivation due to bacterium size constraints. These findings advance the design of tandem photoreactors for dual wastewater purification and energy generation
Removal of diclofenac by UV-B and UV-C light-emitting diodes (LEDs) driven advanced oxidation processes (AOPs): Wavelength dependence, kinetic modelling and energy consumption
(Elsevier, 2023) Pizzichetti, Raffaella; Reynolds, Ken; Pablos, Cristina; Casado, Cintia; Moore, Eric; Stanley, Simon; Marugán, Javier
In this study, the degradation of diclofenac (DCF), a frequently detected non-steroidal pharmaceutical, was evaluated by using UV-B and UV-C (265, 285, and 310 nm) light-emitting diodes (LEDs) alone and in combination with hydrogen peroxide (UV/H2O2) and free chlorine (UV/FC). The degradation of DCF followed a pseudo first-order kinetic, and their trend reflected the pattern of the molar absorption coefficients of the DCF and the oxidants. A positive synergistic factor was found for the UV-LED driven advanced oxidation processes in almost all cases, but despite the higher degradation rates, the overall electricity demand is similar to UV alone due to the oxidants’ energy cost. The rigorous kinetic degradation mechanisms at different wavelengths were proposed for the two processes, UV/H2O2 and UV/FC, where the predicted values were respectively kHO = 9.12 ⋅ 109 M− 1 s − 1 and kCl = 1.30 ⋅ 1010 M− 1 s − 1 . No significant synergy (p > 0.05) was found for the dual-wavelength system (265 + 285 nm), and the time-based constants in all cases changed linearly with lamp intensity. Finally, dissolved organic carbon and phytotoxicity analysis revealed low mineralisation (around 20–30%) associated with the formation of stable dimers and a decrease in toxicity towards tomato and radish seeds. In the main, this work shows the great potential of implementing wavelength-specific LEDs in water treatments and effectively designing the reactor playing with adjustable intensities and kinetic degradation rates.
Rigorous kinetic modelling with explicit radiation absorption effects of the photocatalytic inactivation of bacteria in water using suspended titanium dioxide
(ELSEVIER, 2011) Marugán, Javier; van Grieken, Rafael; Pablos, Cristina; Satuf, M. Lucila; Cassano, Alberto E.; Alfano, Orlando M.
This study is focused on the kinetic modelling of the photocatalytic inactivation of bacteria with suspended TiO2. A rigorous model based on a proposed reaction mechanism and accounting explicitly for the rate of photon absorption has been developed. The application of the general kinetic expression to limiting cases suggests that the interaction bacteria-catalyst can be considered to be weak. In contrast, a complex dependence on the radiation absorption rate must be taken into account, as very different radiation conditions may coexist inside the photoreactor, with high absorption rates in the region near to the radiation entrance window and much lower values on the opposite side of the photoreactor. The model has been successfully validated by experimental data, being able to reproduce the evolution of the concentration of viable bacteria in a wide range of values of TiO2 concentration, irradiation power and initial concentration of bacteria with a normalized root mean square logarithmic error of 5.3 %. The values of the kinetic parameters are independent of the specific reactor setup or the operating conditions and therefore, the model can be used in a predictive way for photoreactor design and scaling-up, as well as for the optimization of other reactor configurations.