Eficiencia del lagunaje profundo como tratamiento para la eliminación de metales pesados en aguas residuales de tipo urbano-industrial

Abstract

An experimental treatment pond for residual waters reclamation with a depth of 4.75 m was set up in 1996. It was continuously fed with urban and industrial wastewater previously treated. Several studies have been carried out in order to provide a better understanding of the internal dynamics of the pond and to optimise its performance. A deep pond treatment, arranged in series with the effluent from a treatment plant (physic-chemical treatment + activated sludge) is a terciary technology which, through natural procedures and without additional energy consumption, improves substantially the chemical and sanitary quality of the water so reclaimed, making it suitable both for potential agricultural reuse as well as discharge into watercourses . In addition, a deep pond acts as a sediment trap for heavy metals. Trace elements are known to bind to particulate matter through adsorption, precipitation, coprecipitation and uptake by biota, thus favouring its removal from the water column and accumulation in the sediments. The natural dynamics of the pond makes possible such processes. pH, slightly alkaline, reducing conditions, temperature, abundant organic matter and availability of inorganic ions are the main variables involved. On the other hand, the depth of the pond and the length of residence time favour the sedimentation processes as well. Mean removal efficiencies for Cr, Fe and Zn concentrations were found to be around 60%.