Fil: Rossetti, Germán Horacio. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina. | En este trabajo se modeló un fotorreactor plano, homogéneo y perfectamente mezclado, activado con radiación solar ultravioleta. Luego, se analizó en forma teórica y experimental la degradación de un contaminante orgánico en solución acuosa por medio de la reacción de foto-Fenton asistida con radiación solar. Para modelar el campo de radiación en el interior del fotorreactor fue necesario conocer las componentes directa y difusa de la radiación que llegan a la ventana de entrada del reactor. Para ello, se recurrió a un modelo teórico computacional que predice dichas componentes. Se estudió en forma teórica y experimental la degradación del ácido fórmico en solución acuosa por medio de la reacción de foto-Fenton asistida con radiación solar. La reacción se llevó a cabo en el fotorreactor solar, perfectamente mezclado, con reciclo y operado en forma discontinua e isotérmica a temperatura ambiente. Se desarrolló un modelo teórico para predecir la concentración del contaminante en función del tiempo, teniendo en cuenta: (i) el campo de radiación dentro del reactor, el cual se modeló considerando un medio homogéneo, participativo y reaccionante y (ii) el modelo cinético para esta reacción, para ello se adoptó un mecanismo de reacción aceptado en la bibliografía específica para la degradación de este compuesto por medio de la reacción de foto-Fenton. Se debe notar que se ha obtenido una degradación de hasta un 80% del compuesto orgánico., Luego, se compararon los valores predichos por el modelo desarrollado y los obtenidos experimentalmente, obteniéndose un error máximo del 9 %. | In the present work, the solar decomposition of formic acid (the model compound) in acidic aqueous solution using the Fenton and the photo-Fenton systems, has been studied. With this purpose, a nonconcentrating, flat-plate solar reactor has been modeled and experimentally validated. The theoretical model is based on: (i) a kinetic model that can account for the dark and the radiation activated reaction rates in a single mathematical expression, (ii) reactant species mass balances that are able to take into account that the irradiated volume (photo-Fenton reaction) may be much smaller than the nonirradiated volume (Fenton reaction), and (iii) a rigorous radiation field model for predicting the local volumetric rate of photon absorption (LVRPA) inside the flat-plate solar reactor, for each value of the solar radiation flux incident at the reactor surface of radiation entrance. The experimental work was performed in an isothermal, well-stirred solar reactor placed inside a batch recycling system having a high-flow-rate recirculating pump and a storage tank. Under the adopted operating conditions, an organic pollutant conversion up to 81% was achieved after one hour of operation. Predictions of the theoretical model were compared with experimental results and a good agreement of the formic acid and hydrogen peroxide concentration evolution was obtained. Deviations between model predictions and experimental data were always lower than 9%. Theoretical and experimental results of the pollutant conversion showed that solar irradiation improves the effectiveness of the Fenton system significantly. | Consejo Nacional de Investigaciones Científicas y Técnicas | Universidad Nacional del Litoral

Se estudió el efecto de la radiación ultravioleta (RUV) sobre dos cepas bacterianas marinas antárticas (UVps y UVvi) en la columna de agua de la caleta Potter (Shetland del Sur, Antártida). Frascos de cuarzo con las cepas en estudio fueron expuestos a la radiación solar en superficie, a 1 m y a 3 m de profundidad. Se realizaron ensayos con exposición directa y con filtros interferenciales que discriminaron la radiación UVA y la UVB. En otros ensayos se simuló una mezcla vertical de 4 m/h. Ambas cepas mostraron una disminución significativa del número de unidades formadoras de colonias, tanto en superficie como a 1 m de profundidad, luego de exponerlas a dosis superficiales de UVB de 8,4 kJ m-2. El estudio con filtros interferenciales mostró una disminución significativa de la viabilidad en ambos tratamientos UV en superficie y a 1 m. La cepa UVps mostró mayor sensibilidad a la UVB que a la UVA. La mezcla vertical amortiguó el daño causado por la UVB cuando la dosis en superficie fue de 4,8 kJ m-2. Este efecto amortiguador no se observó cuando la dosis en superficie fue de 7,7 kJ m-2. Estos resultados muestran que el efecto negativo de la RUV sobre el bacterioplancton sería particularmente importante en el primer metro de profundidad de las aguas costeras antárticas con abundante material particulado en suspensión.<br>The effect of UV radiation on two Antarctic marine bacterial strains (UVps and UVvi) was studied in the water column of Potter Cove (South Shetland, Antarctica). Quartz flasks were filled with the bacterial suspensions and exposed to solar radiation at 0 m, 1 m and 3 m depth. Assays using flasks exposed to direct solar radiation and others using flasks covered with/by interferential filters which discriminate between UVA and UVB, were performed. In other assays, a vertical mixing of 4 m/h was simulated. Both strains showed a significant decrease in viability (expressed as colony - forming units) when exposed to a surface UVB dose of 8.4 kJ m-2. Studies with interferential filters showed a significant decrease at 0 and 1 m depth under both UV treatments. The UVps strain appeared to be more sensitive to UVB than to UVA. Damage produced by UVB was attenuated by the vertical mixing when the surface UVB dose was 4.8 kJ m-2. This effect was not observed when surface UVB dose was 7.7 kJ m-2. These results show that the negative effect caused by UVB radiation on the bacterioplankton would be significant only in the first meter of water column of the Antarctic coastal waters with high levels of suspended particulate material.

El río Frío se ha visto afectado por la contaminación con bolsas plásticas provenientes de la actividad bananera en el municipio, las cuales terminan en el cuerpo de agua por acción del viento, donde se fragmentan debido a factores ambientales que causan su degradación, generando microplásticos. Entender cómo sucede este proceso es esencial para la toma de decisiones, por lo que esta investigación tiene como objetivo evaluar química y físicamente el proceso de degradación del polietileno bajo condiciones de calidad del agua de la cuenca baja del río Frío. Para esto, se identificaron los factores ambientales más influyentes sobre la degradación del PEBD en el río, donde los principales fueron la exposición a radiación UV, la temperatura y calidad del agua en términos de nitratos, pH y fosfatos. Luego, se simularon las condiciones naturales del río mediante un montaje experimental y se analizaron los cambios morfológicos y las variaciones de masa de tres fragmentos de plástico durante 28 días a 10ºC, 25ºC y 40ºC, para un total de 72 fragmentos analizados. Con esta información, se estableció la cinética de degradación del PEBD, obteniendo las constantes de velocidad (k) y las energías de activación (Ea), así como la Ley de velocidad para cada caso. Lo anterior se correlacionó con los factores ambientales antes mencionados y se encontró que la radiación UV fue lo que más influyó sobre la constante de velocidad de la reacción, seguido del aumento de la temperatura y la calidad del agua. Esta información servirá como punto de partida para la construcción de un modelo matemático de la degradación del PEBD en condiciones naturales, facilitando la toma de decisiones acerca de la contaminación de microplásticos en el río Frío, para tomar acción desde la ingeniería ambiental con el uso de estrategias que permitan reducir esta contaminación. | Ingeniero Ambiental | Pregrado | The Frío river has been affected by plastic bags coming from banana industry, which reaches the environment by wind-driven transport and subsequently are fragmented by the effects of environmental factors that cause its degradation, generating microplastics. It is essential to understand how this process works in order to make decisions about it, consequently the main purpose of this research is to evaluate chemically and physically how is the degradation process of LDPE at the river, under water quality conditions of the lower basin of Frío river. To achieve this, the most important environmental factors were identified as UV exposure, water temperature and water quality in terms of nitrates, pH and phosphates. Then, natural river conditions were simulated with an experimental set-up and morphology changes in the material were analyzed along with mass changes of the plastic fragments for 28 days at 10ºC, 25ºC and 40ºC, for a total of 72 fragments analyzed. From this information, it was possible to determine the degradation kinetics of LDPE, obtaining the reaction rate coefficients (k) and the activation energies (Ea), as well as the rate law. Previous results were correlated with the environmental factors mentioned and it was found that UV exposure was the factor that influenced the most on the reaction rate coefficient, followed by the increase on temperature and water quality. This information will also serve as a starting point for the construction of a mathematic model of LDPE degradation under natural conditions, facilitating decision making with regard to the microplastics contamination at Frío river, in order to take action from environmental engineering by using strategies that will allow to reduce this contamination.

Este trabalho objetivou adaptar um método de controle de larvas do mexilhão dourado (Limnoperna fortunei) com a utilização de radiação ultravioleta e verificar seu efeito sobre cianobactérias e cianotoxinas presentes na água. Limnoperna fortunei (Dunker, 1857), conhecido vulgarmente como mexilhão dourado é proveniente do sudeste asiático. Foi, provavelmente, introduzido nos nossos mananciais, não intencionalmente, através da água de lastro, com os primeiros registros na América do Sul, em 1991, no Rio da Prata, nas proximidades de Buenos Aires, Argentina. No Brasil foi visto pela primeira vez na área do Delta do Jacuí, em frente ao porto de Porto Alegre, RS, no ano de 1998. Além de ameaçar à biodiversidade de ecossistemas, vem provocando a obstrução das tubulações e trocadores de calor junto às estações de tratamento de água e indústrias que utilizam água bruta para resfriamento. As estações de tratamento, além de enfrentarem problemas com o entupimento pelo mexilhão, defrontam-se também com as florações de cianobactérias. As florações, conhecidas também como blooms, são eventos de multiplicação e acumulação de microalgas ou cianobactérias nos corpos hídricos, que podem durar de algumas horas ao longo do dia a meses. As cianobactérias podem liberar cianotoxinas que estão presentes principalmente no interior das células, e são liberadas na lise celular, que ocorre principalmente por senescência natural. Os experimentos foram realizados em uma unidade piloto, onde concentrações conhecidas de larvas do mexilhão dourado foram submetidas a doses de radiação ultravioleta, na faixa de 200 a 800 mWs/cm2. As amostras de água bruta utilizadas nos testes foram avaliadas por meio de métodos analíticos adequados (APHA, 2005). Foram determinados os parâmetros de temperatura (°C), pH, turbidez (NTU), dureza (mgCaCO3/L) e sólidos suspensos (mg/L), os quais poderiam influenciar nas condições dos testes. As mesmas condições testadas para o mexilhão foram utilizadas nos experimentos com cianobactérias. As larvas de mexilhão dourado e a água bruta utilizada no experimento foram obtidos no delta do Jacui, Porto Alegre, Rio Grande do Sul, Brasil. A cianobactéria Microcystis aeruginosa, produtora de microcistina, foi cultivada em laboratório. A mortalidade instantânea das larvas aproximou-se dos 100% nas condições do teste com a dosagem de 781mWs/cm2 , com DL50 de 324 mWs/cm2. Na água residual dos experimentos de exposição à radiação UV, foram realizados ensaios ecotoxicológicos crônicos com Pimephales promelas, Ceriodaphnia dubia e Selenastrum capricornutum, a fim de detectar a presença de subprodutos que poderiam gerar toxicidade aos organismos de diferentes níveis tróficos. Os resultados desta avaliação ecotoxicológica não demonstraram toxicidade residual. Os dados obtidos demonstraram-se satisfatórios no controle daslarvas de mexilhão, entretanto não promoveram a lise das células de M. aeruginosa e a conseqüente liberação de microcistinas nas condições testadas. | L. fortunei (Dunker, 1857), commonly known as golden mussel comes from Southeast Asia. It might have been unintentionally introduced in our water sources through ballast water, with the first records in 1991, in Rio de la Plata, near Buenos Aires, Argentina, South America. In Brazil it was first seen in 1998, in Jacuí Delta, opposite Porto Alegre’s harbor. Besides threatening the biodiversity of ecosystems, this mussel has caused the obstruction of pipes and heat exchangers along the water treatment plants and industries that use raw water for cooling. Treatment plants facing problems with the clogging of mussels also have to contend with the cyanobacterial blooms. The blooms are events of multiplication and accumulation of algae or cyanobacteria in water bodies that can last from a few hours to days or months. The cyanobacteria may release cyanotoxins present mainly in cells and are released upon cell lysis, which occurs primarily by natural senescence. Thus, the aim of study is to adapt a control method of golden mussel larvae (L. fortunei) using ultraviolet radiation and verify its effect on cyanobacteria and cyanotoxins in the water. The experiments were performed in a pilot unit, where known concentrations of mussel larvae were subjected to doses of ultraviolet radiation ranging from 200 to 800 mWs/cm2, and the quality of water used, evaluated. The same conditions tested for the mussels were used in experiments with cyanobacteria. Mussel larvae and raw water used in the experiments were obtained from the Jacuí Delta, Porto Alegre, Rio Grande do Sul, Brazil. The cyanobacteria Microcystis aeruginosa, witch produces microcystin, was grown in culture in our laboratory. The instantaneous mortality of larvae was approximately 100% with 781mWs/cm2 in test conditions, with LD50 of 324 mWs/cm2. Ecotoxicological tests were performed with Pimephales promelas, Ceriodaphnia dubia, and Selenastrum capricornutum, to detect the presence of byproducts that could cause toxicity to organisms of different trophic levels in the residual water. The results of ecotoxicological evaluation showed no residual toxicity. The data showed to be satisfactory in larvae control, but did not cause lysis in cells of M. aeruginosa and the consequent release of microcystins in the water.