PRESENCIA DE ARSENICO EN AGUAS DE POZOS PROFUNDOS Y SU REMOCIÓN USANDO UN PROTOTIPO PILOTO BASADO EN COLECTORES SOLARES DE BAJO COSTO
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Inv. y Des.
Abstract
Se ha realizado un relevamiento de la calidad físico-química y presencia de arsénico en aguas de pozos con profundidad mayor a 50 m, ubicados en la zona periurbana oeste de la ciudad de Cochabamba, mediante muestreos llevados a cabo durante dos periodos diferentes (húmedo y seco). Por otra parte, se ejecutó un estudio de desempeño de una planta piloto de tratamiento para la remoción de arsénico (As) basado en la aplicación de colectores solares de bajo costo, construidos con materiales reciclables de fácil accesibilidad. Las aguas subterráneas son del tipo calcio-bicarbonato (Ca-HCO3) por su predominancia sobre otros cationes y aniones, son ligeramente alcalinas (pH 7,4 - 8,3) y sus concentraciones de hierro Fe (II) y manganeso Mn (II) disueltos son relativamente altas, variando entre <0,1 y 2,1 mg/L y <0,1 y 1,2 mg/L, respectivamente. Son moderadamente reductoras, con potencial óxido-reducción (ORP) entre -12,5 y 69 mV. Existe una significativa presencia natural de As. Cerca de la mitad de las muestras presentan valores superiores al valor requerido por la Norma Boliviana de Agua Potable (NB 512) de 10 mg/L. En el periodo seco (8 meses) cerca del 40% de las muestras la superan en más de 10 veces. El desempeño del sistema de tratamiento piloto, mediante el proceso de Remoción Asistida por Oxidación Solar (RAOS), fue satisfactorio incluso en días nublados con remociones mayores al 80%, logrando reducir la concentración de As hasta valores muy por debajo de lo requerido en la Norma Boliviana de agua potable. Existe una remoción muy significativa de As (cerca del 75%) en la trayectoria que va desde la boca de pozo hasta la entrada al sistema de tratamiento. La remoción puede explicarse por la presencia de incrustaciones de óxidos de hierro (III) y manganeso (IV) depositadas en la superficie de la línea de distribución, que incluye tuberías y tanques de almacenamiento, que pueden adsorber los arseniatos formados por la aireación en el trayecto. La aireación con aspersores comerciales domésticos puede lograr efectivamente la oxidación de arsenitos a arseniatos.
The arsenic concentrations and quality of water from 18 deep water wells (above 50 m) located in the west side peri-urban area of Cochabamba, Bolivia have been assessed, together with a study on the performance of a low cost solar collector based pilot plant applied to arsenic removal. The analyzed water samples indicated a calcium-bicarbonate (Ca-HCO3) water type. They are slightly alkaline, ranging from 7,4 to 8,3 with an average of 7,7. The redox sensitive ions concentrations, iron and manganese are relatively high, <0.1-2.1 mg/L (average 0,3 mg/L) and < 0,1 - 1,2 mg/L (average 0,4 mg/L), respectively. They are slightly reductive (ORP in the range of -12,5 and - 69 mV). Arsenic was determined in the same sampling sites and in two different periods (wet and dry seasons) Dissolved arsenic concentrations exceed Bolivian regulations and World Health Organization (WHO) guidelines (10 mg/L) for drinking water in approximately 50% of the wells. Moreover, nearly 40% of the wells exceeded those regulations more than ten times, in samples taken within the dry season (8 months). The performance of the pilot plant, which uses the Solar Oxidation and Removal of Arsenic (SORAS) technique, was satisfactory even in cloudy days, obtaining arsenic removals higher than 80% and As concentrations far below the Bolivian regulations. There exists a significant removal of arsenic (c.a. 75%) in the course from the water well to the entrance to the pilot plant. Such removal occurs due to the adsorption of arsenate ions on iron (III) and manganese (IV) oxides, attached to the surface of the distribution line, including pipes and storage tanks. Aeration with domestic commercial sprinklers can achieve an effective oxidation of arsenite ions to arsenates.
The arsenic concentrations and quality of water from 18 deep water wells (above 50 m) located in the west side peri-urban area of Cochabamba, Bolivia have been assessed, together with a study on the performance of a low cost solar collector based pilot plant applied to arsenic removal. The analyzed water samples indicated a calcium-bicarbonate (Ca-HCO3) water type. They are slightly alkaline, ranging from 7,4 to 8,3 with an average of 7,7. The redox sensitive ions concentrations, iron and manganese are relatively high, <0.1-2.1 mg/L (average 0,3 mg/L) and < 0,1 - 1,2 mg/L (average 0,4 mg/L), respectively. They are slightly reductive (ORP in the range of -12,5 and - 69 mV). Arsenic was determined in the same sampling sites and in two different periods (wet and dry seasons) Dissolved arsenic concentrations exceed Bolivian regulations and World Health Organization (WHO) guidelines (10 mg/L) for drinking water in approximately 50% of the wells. Moreover, nearly 40% of the wells exceeded those regulations more than ten times, in samples taken within the dry season (8 months). The performance of the pilot plant, which uses the Solar Oxidation and Removal of Arsenic (SORAS) technique, was satisfactory even in cloudy days, obtaining arsenic removals higher than 80% and As concentrations far below the Bolivian regulations. There exists a significant removal of arsenic (c.a. 75%) in the course from the water well to the entrance to the pilot plant. Such removal occurs due to the adsorption of arsenate ions on iron (III) and manganese (IV) oxides, attached to the surface of the distribution line, including pipes and storage tanks. Aeration with domestic commercial sprinklers can achieve an effective oxidation of arsenite ions to arsenates.
Description
Vol. 2, No. 14