Solar light and metal-doped TiO₂ to eliminate water-transmitted bacterial pathogens:Photocatalyst characterization and disinfection performance

Summarization: The present study deals with the inactivation of Escherichia coli and Klebsiella pneumoniae in water by means of heterogeneous photocatalysis under simulated solar irradiation. For this purpose, novel Mn-, Co- and Mn/Co-doped TiO2 catalysts were prepared. A straightforward, simple and inexpensive process has been developed based on a co-precipitation method for the synthesis of metal-doped catalysts, which were subsequently assessed in terms of their disinfection efficiency. The effect of various operating conditions, such as metal dopant (Mn-, Co- and Mn/Co), dopant concentration (0.02–1 wt%), catalyst concentration (25–250 mg/L), bacterial concentration (102–108 CFU/mL), treatment time (up to 60 min), toxic effects on bacteria and photon flux (4.93–5.8 × 10−7 Einstein/(L s)), was examined under simulated solar irradiation. Metal-doped TiO2 samples were prepared reproducibly and doping shifted the optical absorption edge to the visible region. Their activity was superior to the respective of commercially available P25 titania. The reference strains of E. coli and K. pneumoniae proved to be readily inactivated during photocatalytic treatment of aqueous samples, since disinfection occurred rapidly (i.e. after only 10 min of irradiation) with the dopant concentration affecting the overall process to a certain extent. Disinfection follows a pseudo-first order kinetic rate in terms of both bacteria removal. Inactivation of the bacteria is attributed to the oxidative degradation of their cells and increase of their cell permeability and not to the potential toxicity of the metal-doped semiconductors, which did not exhibit any bactericidal properties. It has been shown that the improved activity of the Mn-, Co-, and binary Mn/Co doped TiO2 is accredited to the fact that they can be activated in the visible part of the spectrum, in the absence of UV light (i.e. >420 nm).Presented on: Applied Catalysis B: Environmenta

Effect of metal doped and co-doped TiO2 photocatalysts oriented to degrade indoor/outdoor pollutants for air quality improvement. A kinetic and product study using acetaldehyde as probe molecule

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Study of generated genetic polymorphisms during the photocatalytic elimination of Klebsiella pneumoniae in water

Summarization: Klebsiella pneumoniae is considered to be an emerging pathogen persisting under extreme environmentally stressed conditions. The aim of the present study is the investigation of inactivation rates of this pathogen in water by means of heterogeneous photocatalytic treatment under solar irradiation and the induced genetic variance applying RAPD-PCR as a molecular typing tool. Novel Mn- and Co-doped TiO2 catalysts were assessed in terms of their disinfection efficiency. The reference strain of K. pneumoniae proved to be readily inactivated, since disinfection occurred rapidly (i.e. after only 10 min of treatment) and low levels of bacterial regrowth were recorded in the dark and under natural sunlight. Binary doped titania exhibited the best photocatalytic activity, verifying the synergistic effect induced by composite dopants. Applying RAPD analysis to viable cells after treatment we concluded that increasing the treatment time led to considerable alteration of RAPD profiles and the homology coefficient ranged almost between 35 and 60%. RAPD-PCR proved to be a useful typing molecular tool that under standardized conditions exhibits highly reproducible results. Genetic variation among isolates increased in relation to the period of treatment and prolonged irradiation in each case affected the overall alteration in band patterns. RAPD patterns were highly diverse between treated and untreated isolates when disinfection was performed with the Co-doped titania. The broad spectrum of genetic variance and generated polymorphisms has the potential to increase the already significant virulence of the species.Presented on: Photochemical & Photobiological Sciences Photochemical and Photobiological Science

Inactivation of MS2 coliphage in sewage by solar photocatalysis using metal-doped TiO2

Summarization: The beneficial properties of metal-doped titania nanoparticles with respect to wastewater disinfection under solar irradiation were investigated. Mn-, Co- and binary Mn/Co-doped TiO2 catalysts were prepared by means of a co-precipitation method and were subsequently assessed in terms of their potential to inactivate MS2 bacteriophage in slurry reactor under simulated and natural solar irradiation. Disinfection effectiveness was evaluated in relation to influential operating parameters, like catalyst type (Mn-, Co- and Mn/Co), dopant concentration (0.02–1 mol wt%), artificial and natural solar light, wavelength (i.e. >420 nm) and photon flux (4.93–5.8 × 10−7 E/(L s)). Metal doping led to considerable narrowing of the band gap and the spectral response of the catalysts extended well into the visible region. MS2 phage was readily inactivated in sewage samples under simulated solar irradiation in the presence of the prepared metal-doped catalysts. The latter proved to be superior to the commercial P25, under the current experimental conditions, resulting in an approximately 60% phage population decrease in almost 60 min of simulated solar irradiation when initial MS2 concentration was 105 PFU/mL. Catalysts with the binary dopant exhibited the best photocatalytic activity in all cases, as almost 99% of MS2 population was eliminated in less than 20 min of irradiation highlighting the fact that composite dopants induce a synergistic effect. The effect of different dopants concentration was apparent up to a certain limit. Disinfection follows a pseudo-first order kinetic rate. Retardation of the process by a factor 1.6–3.8 was recorded under natural solar light, based on the kinetic rate constants of inactivation curves which were within the range of 0.032–0.057 min−1. The corresponding range for inactivation under simulated solar irradiation was 0.053–0.221 min−1. Moreover, testing the Mn-, Co-, and binary Mn/Co doped TiO2 in the absence of UV light, they were considerably sensitized making clear that they can be activated in the visible part of the spectrum.Presented on: Applied Catalysis B: Environmenta

Solar photocatalysis as disinfection technique: inactivation of Klebsiella pneumoniae in sewage and investigation of changes in antibiotic resistance profile

Summarization: The presence of pathogenic microorganisms in wastewater and their resistant nature to antibiotics impose effective disinfection treatment for public health and environmental protection. In this work, photocatalysis with metal-doped titania under artificial and natural sunlight, chlorination and UV-C irradiation were evaluated for their potential to inactivate Klebsiella pneumoniae in real wastewater. Their overall effect on antibiotic resistance profile and target antibiotic resistance genes (ARGs) was also investigated. In particular, Mn-, Co- and binary Mn/Co-TiO2 were tested resulting in bacterial decrease from 4 to 6 Logs upon 90 min of exposure to simulated solar irradiation. The response of catalysts under natural solar light was insufficient, as only a 2 Log reduction was recorded even after 60 min of treatment. The relative activity of the applied methods for K. pneumoniae inactivation was decreased in the order: photocatalysis with the binary Co/Mn-TiO2 under artificial light > chlorination with dose of 5 mg/L of free chlorine > UV-C irradiation, at an initial bacterial concentration of 107 CFU/mL. The applied methods showed various effects on antibiotic resistance profile in residual cells. Among the tested antibiotics (ampicillin, cefaclor, sulfamethoxazole and tetracycline), considerable changes in MIC values were recorded for cefaclor and tetracycline. Resistance of surviving cells after treatment remained in high levels, reflecting the abundance of the corresponding target ARGs, namely tetA, tetM, sul1, blaTEM and ampC. The notable presence of target ARGs post disinfection raises concerns and makes wastewater effluent a carrier of antibiotic resistance elements into the aquatic environment.Παρουσιάστηκε στο: Journal of Environmental Managemen

Inactivation of Staphylococcus aureus in water by means of solar photocatalysis using metal doped TiO2 semiconductors

Summarization: The need for clean water and high hygiene standards has led to the exploration of effective disinfection techniques for the elimination of persistent and pathogenic microorganisms. The disinfection potential of cation-doped titania was investigated in terms of Staphylococcus aureus elimination in aqueous samples under artificial and natural sunlight. RESULTS: Fe-, Al- and Cr-doped TiO2 were prepared with dopant loadings of 0.04, 0.3 and 2 wt%. Cation doping resulted in absorption shifts into the visible region, thus rendering the use of solar light feasible. The relative activity for S. aureus inactivation decreased in the order Fe-TiO2 > Al-TiO2 > Cr-TiO2 > P25. For example, an approximately 5 log reduction was obtained in 30, 10 and 6 min when Fe-loading was 0.04, 0.3 and 2 wt%, respectively, at an initial bacterial concentration of 107 CFU mL−1 and a catalyst concentration of 50 mg L−1. The catalyst concentration in each case affected the overall process up to a certain extent. Scanning electron microscopy revealed interaction between the catalyst nanoparticles and bacterial cells during treatment, with significant alteration in their shape, morphology and size. Under natural sunlight conditions Fe-TiO2 and Al-TiO2 could achieve a 99.9% killing of S. aureus population after 60 min. CONCLUSION: In a nutshell, solar photocatlysis with cation-doped titania is an effective disinfection technology for adaptable and tolerant pathogens such as S. aureus.Presented on: Journal of Chemical Technology and Biotechnolog