Hydraulic performance of a deep stabilisation pond fed at 3.5 m depth

The hydraulic internal behavior of a deep wastewater stabilization pond fed at 3.5 m depth is studied. The lagoon is situated in the Region of Murcia (Southeast Spain) and this behavior was studied before by the authors when wastewater entered at surface level [Torres J. J., Soler A., Sáez J. and Ortuño J. F. (1997a). Hydraulic performance of a deep wastewater stabilization pond. Water Res. 31(4), 679–688.] The tracer used in this experiment was sulforhodamine B. Two experiments were carried out, one in winter and the other in summer. In both cases it was found that since the sewage water temperature was higher than that of the water of the deepest part of the lagoon, an active thermal current was formed which rapidly transported the feed to the surface. On account of this, the phenomenon is very similar to that in the case of the surface feed. The active zone of the system is located from surface to 1 m depth and behaves like a constant stirred tank reactor (CSTR). The average winter and summer volumes of this active layer have been estimated. It has also been observed that the short-circuits have been minimal.