Jorge Martín Meichtry

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El suministro de agua es imprescindible para cubrir las necesidades básicas de la población y fomentar el desarrollo socioeconómico. No obstante, los acuíferos están expuestos a una creciente problemática de agotamiento y contaminación. Para evaluar el estado del agua, se utiliza un índice de calidad que toma en cuenta múltiples parámetros físicos, químicos y biológicos, y se plasman en una fórmula matemática y en un período determinado. Además, este índice permite hacer un análisis global de la calidad del agua en diferentes niveles, y determinar la vulnerabilidad del cuerpo de agua frente a posibles amenazas. El objetivo de este trabajo consiste en examinar la calidad del agua subterránea en la zona centro oeste de la provincia de Santa Fe, Argentina, empleando un índice de calidad (ICA) que refleje su verdadero estado. De esta forma, se calcula el ICA lo que permite clasificarla en términos de su aptitud para el consumo humano, según las categorías de excelente, buena, pobre, muy pobre y no apta. Se realizaron muestreos en distintos puntos de la zona en estudio en un período comprendido entre 2021 y 2022, y las muestras tomadas se caracterizaron fisicoquímicamente. Para el cálculo de ICA, se utilizaron siete parámetros fisicoquímicos, a los que se les asignó una ponderación acorde con su importancia relativa en la calidad del agua y en función de los efectos adversos en la salud humana. Los resultados obtenidos demostraron que el mayor porcentaje de muestras analizadas se encuentra dentro de la clasificación “muy pobre” y “no apta para consumo humano”. El ICA permitió demostrar que, en general, es aceptable la calidad química del agua subterránea de la región centro oeste de la provincia de Santa Fe, Argentina, con fines de abastecimiento. Por lo que es conveniente diseñar un esquema de monitoreo que refleje las eventuales variaciones de la calidad y cantidad del recurso, lo que permitirá utilizar medidas correctivas y/o paliativas ante su deterioro.

The photocatalytic activity of undoped and N-doped TiO₂ anatase films with different thicknesses prepared by cathodic arc deposition on glass substrates is reported. After TiO₂ deposition, the doping of the films was carried out by plasma immersion ion implantation in a nitrogen environment. The composition of the films was studied by x-ray photoelectron spectroscopy, the surface morphology was analyzed by atomic force microscopy and the crystalline structure was examined by x-ray diffraction. The thickness was determined by observing the film cross section with scanning electron microscopy. The transmittance of the films in the UV-Vis range was studied as well. The photocatalytic activity of the films was evaluated through the efficiency in the reduction of Cr(VI) in the presence of ethylenediaminetetraacetic acid under UV-Vis irradiation. N-doped films presented a higher photocatalytic efficiency than undoped films: Cr(VI) reduction after 5 h irradiation augmented from 58% (pure TiO₂) to 85% (N-doped TiO₂) for films of 300 nm thickness, and from 69% to 85% for films with a thickness of 440 nm. On the other hand, pure TiO₂ films of 790 nm thickness were more efficient (99% of Cr(VI) reduction) but the effect of doping on the photocatalytic activity was negligible.

The presence of arsenic in water for human consumption is of concern, especially in developing countries, and the design of simple and economic treatments for arsenic removal is imperative. In this paper, three low-cost technologies were evaluated for As(V) or As(III) (5 mg L⁻¹) removal: (1) zerovalent iron (Fe(0)), as powdered (μFe(0)) and iron wool (wFe(0)); (2) coagulation-flocculation with Al₂(SO₄)₃ or FeCl₃; and (3) adsorption on a natural clay. μFe(0) was more efficient than wFe(0), requiring a minimal dose of 0.25 g L⁻¹ to achieve [As(V)] < 0.01 mg L⁻¹ after 288 h; the reaction time was reduced to 168 h under stirring. When starting from As(III), partial oxidation to As(V) was observed, and removal was not complete even after 648 h with 1 g L⁻¹ μFe(0). As(V) removal using FeCl₃ and Al₂(SO₄)₃ was very fast and completed in 15 min with 0.25 g L⁻¹ of both reagents. However, Al₂(SO₄)₃ was not efficient to remove As(III). With the clay, doses higher than 50 g L⁻¹ and times longer than 648 h were needed to remove both As species. Arsenic leached from μFe(0) used to treat As(III) was almost negligible. Thus, Fe(0) may be the best alternative for low-cost, small-scale applications.

Background: Thiomersal (TM), a complex between 2-mercaptobenzoic acid (2-MBA) and ethylmercury (C2H5Hg⁺), is an antimicrobial preservative used in immunological, ophthalmic, cosmetic products, and vaccines. Objective: TM has been treated by UV/TiO₂ photocatalysis in the presence or absence of oxygen at acidic pH. C₂H₅Hg⁺, 2-MBA, and 2-sulfobenzoic acid (2-SBA) were found as products. A 2-SBA photocatalytic treatment was undertaken to study sulfur evolution. Methods: Photocatalytic runs were performed using a UVA lamp (λmax = 352 nm), open to the air or under N₂. A suspension of the corresponding TM or 2-SBA salt and TiO₂ was prepared, and pH was adjusted. Suspensions were stirred in the dark for 30 min and then irradiated. TM, 2-MBA, 2-SBA, and C₂H₅Hg⁺ were quantified by HPLC, sulfur by TXRF, and the deposits on the photocatalyst were analyzed by chemical reactions. The mineralization degree was followed by TOC. Sulfate was determined using BaCl₂ at 580 nm. Results: Photocatalytic destruction of TM and total C₂H₅Hg⁺ was complete under N₂ and air, but TM degradation was much faster in air. The evolution of TM and the products followed a pseudo-first-order kinetics. Conclusion: TiO₂-photocatalytic degradation is a suitable technique for the treatment of TM and its degradation products. In contrast to other organomercurial compounds, TM degradation is faster in the presence of O₂, indicating that the oxidative mechanism is the preferred pathway. A significant TM mineralization (> 60%, NPOC and total S) was obtained. TM was more easily degraded than 2-SBA. Sulfate was the final product.