No abstract

Background. The development of alternative processes to eliminate pathogenic agents in water is a matter of growing interest. Current drinking water disinfection procedures, such as chlorination and ozonation, can generate disinfection by-products with carcinogenic and mutagenic potential and are not readily applicable in isolated rural communities of less-favored countries. Solar disinfection processes are of particular interest to water treatment in sunny regions of the Earth. Solar light may be used to activate a photocatalyst or photosensitizer that generates, in the presence of molecular oxygen dissolved in water, reactive oxygen species (ROS), such as the HO• radical, singlet oxygen (O21), or superoxide (O2•), which are toxic to waterborne microorganisms. Method of Approach. Wild and collection-type Escherichia coli have been selected as model bacteria. Inactivation of such bacteria by either TiO2 nanoparticles, water-soluble tris(2,2′-bipyridine)ruthenium(II) dichloride or Rose bengal (RB) subject to simulated sunlight have been compared. Although TiO2 is the prototypical material for heterogeneous photocatalysis, the other two dyes are known to generate significant amounts of O21 by photosensitization but have different chemical structures. The concentration of dye, illumination time, photostability, presence of scavengers, and post-treatment regrowth of bacteria have been investigated. Results. After 1hr of solar illumination the Ru(II) complex produced a strong loss of E. coli culturability monitored with solid selective agars. Both the collection- and wild-type bacteria are sensitive to the treatment with 2-10mgL−1 of dye. This photosensitizer showed a better inactivation effect than TiO2 and the anionic organic dye RB due to a combination of visible light absorption, photostability, and production of O21 and other ROS when bound to the bacterial membrane. A complete loss of culturability was observed when the initial concentration was 103CFUmL−1, with no bacteria regrowth detected after 24hr of the water treatment. At higher initial microorganism levels, culturability still remains and regrowth is observed. Scavengers show that the HO• radical is not involved in bacteria inactivation by photosensitization. Conclusions. A higher quantum yield of ROS generation by the sensitizing dyes compared to the semiconductor photocatalyst determines the faster sunlight-activated water disinfection of photodynamic processes. The homogeneous nature of the latter determines a more efficient interaction of the toxic intermediates with the target microorganisms. Solid supporting of the Ru(II) dye is expected to eliminate the potentials problems associated to the water-soluble dye.

In this study, the performance of zinc oxide as a catalyst for photodegradation of commercial herbicide 2,4-D AMINA 4

Global quantum yield and overall volumetric rate of photon absorption (OVRPA) were quantified for TiO

Most of dyes are considered as non - biodegradable substances and because this, they have became in an environmental problem. Commercial dyes are used in paper and textile industries, and their by-products contaminate surface water sources. Titanium dioxide - based photocatalysis can be an alternative for treatment of dye - contaminated water streams before dumping, because this process can generate powerful oxidant species as hydroxyl free radicals (•OH). In this study, the photocatalytic decolorization of methylene blue was carried out in a compound parabolic collector (CPC) and tubular collector (TC; no reflectors) using the radiation provided by a set of six UV black-lamps. The experimental tests corresponding to a central-composite experimental design were carried out during three hours, whereas the tests for optimal conditions were carried out during 315 min. The decolorization of the dye was measured indirectly with UV- visible absorbance. The optimal region could be determined using the Response Surface Methodology, and for CPC reactor the results were 70.8% for optimal degradation at 0.44 g/L of TiO

Se obtuvo una solución de la ecuación de Rachford Rice Generalizada (R-RG) para múltiples fases y múltiples componentes, usando un planteamiento numérico que acopló un método modificado de Newton-Raphson, un parámetro de amortiguamiento tipo Broyden (obtenido a partir de la Norma Euclidiana del vector de funciones residuales R-RG) y el concepto de Flash negativo, el cual condicionó la naturaleza positiva de las fracciones de los componentes en las fases resultantes. Esta solución se probó con sistemas hipotéticos de P fases y N componentes generados aleatoriamente, al igual que los vectores de valor inicial. Se encontró que la solución propuesta es altamente estable y convergente para cualquier tipo de vector de inicio y que el número de iteraciones es afectado críticamente por éste vector y no necesariamente por la cantidad de fases o número de componentes.

No abstract

Recebido em 28/8/09; aceito em 23/4/09; publicado na web em 9/8/10In this work, TiO 2 photocatalysis was used to disinfect domestic wastewaters previously treated by different biological treatment systems: Upward-flow Anaerobic Sludge Blanket (UASB), facultative pond, and duckweed pond. The microorganisms monitored were E. coli, total coliforms, Shigella species, and Salmonella species. Photocatalytic experiments were carried out using two light sources: a solar simulator (UV intensity: 68-70 W m ). Samples were taken after each treatment stage. Results indicate that bacterial photocatalytic inactivation is affected by characteristics of the effluent, including turbidity, concentration of organic matter, and bacterial concentration, which depend of the type of biological pretreatment previously used.