Fe vs. TiO2 Photo-assisted Processes for Enhancing the Solar Inactivation of Bacteria in Water

Batch solar water disinfection (SODIS) is a known, simple and low-cost water treatment technology. SODIS is based on the synergistic action of temperature increase and light-assisted generation of Reactive Oxygen Species (ROS) on bacteria. ROS are generated via the action of solar photons on i) Natural Organic Matter (NOM), ii) some mineral components of water (Fe oxides or Fe-organic complexes, nitrogen compounds) and iii) endogenous bacteria photosensitizers (e.g. cytochrome). SODIS has proven its effectiveness for remote settlements or urban slums in regions with high incident solar radiation. All of the internal and external simultaneous processes are often driven by photoactive Fe-species present in the cell, as well as in the natural water sources. In SODIS, a temperature of 50 °C is required and due to this temperature dependence, only 1–2 L can be treated at a time. As required exposure time strongly depends on irradiation intensity and temperature, some SODIS households could be overburdened, leading to inadequate treatment and probable bacterial re-growth. This is why TiO2 photocatalysis and Fe photo-assisted systems (i.e. photo-Fenton reactants) have been considered to enhance the photo-catalytic processes already present in natural water sources when exposed to solar light. Both TiO2 and Fe-photoassisted processes, when applied to water disinfection aim to improve the performance of solar bacteria inactivation systems by i) enhancing ROS production, ii) making the process independent from the rise in temperature and as a consequence iii) allowing the treatment of larger volumes than 1–2 L of water and iv) prevent bacterial (re)growth, sometimes observed after sole solar treatment

Ultrasound enhancement of near-neutral photo-Fenton for effective E. coli inactivation in wastewater

In this study, we attempt for the first time to couple sonication and photo-Fenton for bacterial inactivation of secondary treated effluent. Synthetic wastewater was subjected to sequential high-frequency/low power sonication, followed by mild photo-Fenton treatment, under a solar simulator. It was followed by the assessment of the contribution of each component of the process (Fenton, US, hv) towards the removal rate and the long-term survival; sunlight greatly improved the treatment efficiency, with the coupled process being the only one to yield total inactivation within the 4-h period of treatment. The short-term beneficial disinfecting action of US and its detrimental effect on bacterial survival in long term, as well as the impact of light addition were also revealed. Finally, an investigation on the operational parameters of the process was performed, to investigate possible improvement and/or limitations of the coupled treatment; 3 levels of each parameter involved (hydraulic, environmental, US and Fenton) were tested. Only H2O2 increased improved the process significantly, but the action mode of the joint process indicated potential cost-effective solutions towards the implementation of this method. (C) 2014 Elsevier B.V. All rights reserved.Preprin

Proyecto de intervención 1 : construcción del plan de estudios del área de filosofía, para la media académica del colegio Liceo Andino, con un enfoque lúdico

El proyecto de intervención realizado, busca resolver, a partir del replanteamiento del problema que surge al pensar en la articulación de filosofía y pedagogía, reformulando la pregunta del porqué por el para qué. De esta forma, con la articulación de estas dos disciplinas, se elaboró una propuesta que integró la lúdica como herramienta pedagógica en un plan de estudios de filosofía, construido a partir de las Orientaciones Pedagógicas del Ministerio de Educación Nacional establecidas para dicha área. El propósito de dicho proyecto fue atender las necesidades y dificultades académicas particulares que los estudiantes de la media, del Liceo Andino, tenían con la apropiación y aprendizaje de los temas y contenidos de Filosofía. Finalmente, el presente proyecto de intervención disciplinar (PID) hace especial énfasis en la necesidad de apuntar a desarrollar las competencias crítica, dialógica y creativa con el objetivo de desarrollar en los estudiantes la habilidad del pensamiento crítico, a través de la integración de la lúdica en la práctica docente. De esta forma, el plan de estudios construido deja la base teórica y la guía para que cualquier docente de filosofía pueda construir uno que se ajuste a las necesidades y dificultades académicas de la institución donde orienta dicha área.The intervention project carried out, seeks to solve, from the rethinking of the problem that arises when thinking about the articulation of philosophy and pedagogy, reformulating the question of why. In this way, with the articulation of these two disciplines, a proposal was developed that integrated play as a pedagogical tool in a philosophy study plan, built from the Pedagogical Orientations of the Ministry of National Education established for that area. The purpose of this project was to attend to the particular academic needs and difficulties that the high school students, from the Liceo Andino, had with the appropriation and learning of the topics and contents of Philosophy. Finally, the present disciplinary intervention project (PID) places special emphasis on the need to aim to develop critical, dialogic and creative competences with the aim of developing in students the ability of critical thinking, through the integration of play in teaching practice. In this way, the built study plan leaves the theoretical base and the guide so that any philosophy teacher can build one that adjusts to the academic needs and difficulties of the institution where he or she guides said area

Monitoring the post-irradiation E-coli survival patterns in environmental water matrices: implications in handling solar disinfected wastewater

In this study, simulated solar disinfection of secondary effluent was followed by dark storage at different temperatures or different receiving water matrices. Escherichia coil illumination was followed by 3-day monitoring of the bacterial population and its adaptation in different temperature conditions in the dark. The subsequent survival was linked to the dose received during exposure to light, and results were obtained on the environmentally induced prolongation of survival, maintenance of population or excessive growth, at 4 degrees C, 20 degrees C and 37 degrees C, respectively. An additional set of experiments at 20 degrees C was subjected to dilution in E. coli-free synthetic wastewater, water from Lake Leman, (synthetic) seawater and Mili-Q water. Post-irradiation monitoring was also conducted, studying 50%, 10% and 1% dilution rates, and the results were attributed to the two parameters of dilution medium and dilution ratio. However, different responses were found based on the acquired dose during pre-treatment. This indicates the importance of the illumination prior to storage, and the preference of bacteria in some matrices over the others. Survival was linked to initial population, dose, dilution and medium; shorter illumination times are to be considered according to the receiving water matrix. (C) 2014 Elsevier B.V. All rights reserved.Postprint (published version

Novel FeOx–polyethylene transparent films: synthesis and mechanism of surface regeneration

The first evidence for the synthesis of a uniform, adhesive polyethylene–FeOx (PE–FeOx) surface leading efficiently to bacterial inactivation is addressed in this study. PE was loaded with 0.04–0.08% Fe wt/wt PE after RF-plasma pretreatment was required to increase the active sites/polarity and roughness to adhere FeOx on PE. The repetitive bacterial inactivation proceeded in a stable way for several cycles. The oxidative radicals leading to bacterial inactivation under aerobic/anaerobic conditions were investigated by the use of appropriate scavengers. By X-ray photoelectron spectroscopy (XPS) and diffuse reflection spectroscopy (DRS) the changes on the PE–FeOx oxidation states and spectroscopic features during bacterial inactivation were monitored. The regeneration of the initial Fe-oxidation state and consequently of the initial Fe-oxidation state in the PE–FeOx was possible and followed by DRS. Inductive plasma coupled mass spectrometry (ICP-MS) indicated that only sub-ppb levels of Fe were released from the PE–FeOx surface within the reaction time

New evidence for Cu-decorated binary-oxides mediating bacterial inactivation/mineralization in aerobic media

Binary oxide semiconductors TiO2-ZrO2 and Cu-decorated TiO2-ZrO2 (TiO2-ZrO2-Cu) uniform films were sputtered on polyester (PES). These films were irradiated under low intensity solar simulated light and led to bacterial inactivation in aerobic and anaerobic media as evaluated by CFU-plate counting. But bacterial mineralization was only induced by TiO2-ZrO2-Cu in aerobic media. The highly oxidative radicals generated on the films surface under light were identified by the use of appropriate scavengers. The hole generated on the TiO2-ZrO2 films is shown to be the main specie leading to bacterial inactivation. TiO2-ZrO2 and Cu-decorated TiO2-ZrO2 films release Zr and Ti< 1ppb and Cu 4.6 ppb/cm2 as determined by inductively coupled plasma mass spectrometry (ICP-MS) This level is far below the citotoxicity permitted level allowed for mammalian cells suggesting that bacterial disinfection proceeds through an oligodynamic effect. By Fourier transform attenuated infrared spectroscopy (ATR-FTIR) the systematic shift of the predominating vs(CH2) vibrational-rotational peak making up most of the bacterial cell-wall content in C was monitored. Based on this evidence a mechanism suggested leading to C-H bond stretching followed by cell lysis and cell death. Bacterial inactivation cycling was observed on TiO2-ZrO2-Cu showing the stability of these films leading to bacterial inactivation

Elucidating bacterial regrowth: Effect of disinfection conditions in dark storage of solar treated secondary effluent

In this study, we systematically investigate solar disinfection of synthetic secondary wastewater, with the effort to decrypt the effects disinfection conditions have on post-irradiation bacterial regrowth in the dark. A full factorial design of 240 experiments was employed to investigate the effects of (i) exposure time (1, 2, 3 and 4 h), (ii) treatment temperature (20, 30, 40, 50 and 60 °C), (iii) initial bacterial concentration (10 3, 104, 105 and 106 CFU/mL) and (iv) sunlight intensity (0, 800 and 1200 W/m2) on Escherichia coli survival for a subsequent 48-h dark control period. The decisive implications treatment temperature inflicted in regrowth were monitored and interpreted within two temperature ranges, from 20 to 40 °C and 40 to 60 °C. In dark tests, bacterial populations presented initial moderate growths at 20-40 °C range, followed by intense regrowth. At 40-60 °C range, acute thermal inactivation without long-term regrowth predominated at 50 °C and was total at 60 °C, within the 4-h treatment period. Introduction of light resulted in higher removal rates or permanent inactivation for 800 and/or 1200 W/m 2, respectively. No post-treatment regrowth in the dark was observed after 24 and 48 h, in completely inactivated samples, and its demonstration, when observed, was well correlated to the bacterial numbers at the end of the disinfection period. Statistical observations on the transferred bacterial populations from day to day are also discussed in this paper

Solar disinfection is an augmentable, in situ-generated photo-Fenton reaction—Part 1: A review of the mechanisms and the fundamental aspects of the process

The present manuscript is a conceptual review concerning the photo-Fenton reaction at near-neutral pH, used for bacterial inactivation. In this first Part, an overview of the mechanisms involved, as well as the fundamental concepts governing the near-neutral photo-Fenton reaction are critically assessed. The two constituents of the process, namely solar light and the Fenton reagents, are dissociated, with their direct and indirect actions thoroughly analyzed. The effects of UVB and UVA on the bacterial cell are firstly discussed, followed by the presentation of the indirect oxidative stress-related inactivation mechanisms initiated into the microorganism, in presence of light. Afterwards, the effect of each Fenton reagent (H2O2, Fe) is analyzed in a step-wise manner, with H2O2 and Fe as enhancements of the solar disinfection mode of action. This approach proves that in fact, the solar photo-Fenton reaction is an enhanced solar disinfection process. Finally, the photo-Fenton reaction is put into context by considering the possible interactions of the separate parts of the combined process with the constituents of the natural environment that can play an important role in the evolution of the bacterial inactivation. (C) 2016 Elsevier B.V. All rights reserved

Supported TiO2 films deposited at different energies: Implications of the surface compactness on the catalytic kinetics

Insight is provided in this study for the effect of the TiO2film densification/compactness on polyethy-lene (PE-TiO2) by sputtering TiO2at two very different energy levels. Uniform, adhesive low energy filmswere prepared by direct current magnetron sputtering (DCMS) and compared with films sputtered athigh energy levels by high power impulse magnetron sputtering (HIPIMS). Nano-particulate TiO2filmssputtered by HPIMS presented sizes of ∼10.2 nm compared to films sputtered by DCMS with TiO2sizesof ∼16.5 nm as determined by X-ray diffraction (XRD). The E. coli inactivation kinetics was three timesfaster for the samples sputtered by HIPIMS compared to their DCMS counterparts. This is an unexpectedfinding since the DCMS presenting larger TiO2sized nanoparticles released a higher amount of Ti-ionscompared to the HIPIMS samples as monitored by inductively coupled plasma mass-spectrometry (ICP-MS). The Ti-ions released do not seem to react through an oligodynamic effect but diffuse through theless compact TiO2sputtered by DCMS. The faster bacterial inactivation kinetics observed by the HIPIMSsputtered samples can be understood in terms of the complete of Ti4+/Ti3+redox conversion during bacte-rial inactivation detected by X-ray photo-electron spectroscopy (XPS) compared to the smaller Ti4+/Ti3+effect observed in the DCMS-samples. A higher optical density was detected for the HIPIMS sputteredsamples by diffuse reflectance spectroscopy (DRS). Evidence is presented for the shift in surface potentialand local pH during bacterial inactivation under aerobic and anaerobic conditions. A reaction mechanismis suggested based on the findings described in this study. The sputtered films present the potential tohinder biofilm formation on flexible thin polymers/textiles widely used in hospitals and health facilities

Aplicación de procesos foto-Fenton a pH neutro en la desinfección de aguas superficiales naturales

En este trabajo se evaluó sistemáticamente a escala de laboratorio usando agua ultrapura y muestras de agua superficial natural, el efecto de los procesos foto-Fenton a pH neutro en la inactivación de células bacterianas.Centro de Investigación y Desarrollo en Ciencias Aplicada