The most efficient system of horizontal subsurface flow constructed wetlands (HSSFCW) for removing dissolved organic carbon (DOC) in the presence of chlorothalonil pesticide (CLT) present in synthetic domestic wastewater was determined using the macrophyte Phragmites australis. Two concentrations of CLT (85 and 385 μg L) and one concentration of glucose (20 mg L) were evaluated in four pilot scale horizontal surface flow constructed wetlands coupled with two sizes of silica gravel, igneous gravel, fine chalky gravel (3.18-6.35 mm), coarse gravel (12.70-25.40 mm) and two water surface heights (20 and 40 cm). For a month, wetlands were acclimated with domestic wastewater. Some groups of bacteria were also identified in the biofilm attached to the gravel. In each treatment periodic samplings were conducted in the influent and effluent. Chlorothalonil was quantified by gas chromatography (GC-ECD m), DOC by an organic carbon analyzer and bacterial groups using conventional microbiology in accordance with Standard Methods. The largest removals of DOC (85.82%-85.31%) were found when using fine gravel (3.18-6.35 mm) and the lower layer of water (20 cm). The bacterial groups quantified in the biofilm were total heterotrophic, revivable heterotrophic, Pseudomonas and total coliforms. The results of this study indicate that fine grain gravel (3.18-6.35 mm) and both water levels (20 to 40 cm) can be used in the removal of organic matter and for the treatment of agricultural effluents contaminated with organo-chloride pesticides like CLT in HSSFCW.
A escala de laboratorio se evaluó la degradación del clorotalonilo (CLT) por un consorcio microbiano aislado de la biopelícula formada en la grava de humedales construidos de flujo subsuperficial horizontal, usados para el tratamiento de agua residual agrícola, y se estimó el efecto del plaguicida en la dinámica de crecimiento de la comunidad de heterótrofos totales (HT) y la población de Pseudomonas spp. Una concentración de CTL de 0,6 mg l-1 y dos niveles de concentración de carbono orgánico disuelto (COD) de 20 y 100 mg l-1 (empleando glucosa como fuente de carbono), fueron usados en la experimentación llevada a cabo en una solución de agua residual sintética. Las variables respuesta fueron: concentración residual de CLT, concentración residual de COD, y recuento de unidades formadoras de colonias (UFC) de las poblaciones de HT y Pseudomonas spp. Las variables control que se midieron durante el proceso para determinar cambios en las condiciones fisicoquímicas del medio, fueron: conductividad eléctrica, oxígeno disuelto, pH y potencial redox. Se comprobó que el nivel de concentración de carbono orgánico afectó notablemente la degradación del CLT. Con 100 mg l-1 de COD se alcanzó 99,7% de degradación de CLT a las 168 horas del ensayo; en tanto que 45,1%, se alcanzó con 20 mg l-1 de COD. En el análisis cromatográfico no se detectaron productos de degradación.
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