Hydraulic performance of a deep wastewater stabilization pond

The hydraulic performance of a deep wastewater stabilization pond located in the Espinardo Campus of the University of Murcia was studied. The pond has a maximum capacity of 15,000 m3, with a maximum depth of 8 m. Sulforhodamine B dye is used as a tracer in the experimental study, which was carried out in two different climatic periods, winter and summer, so that the influence of temperature on the internal hydrodynamic of the lagoon could be ascertained. Two types of sample were obtained. One was taken from the mass of water within the pond and the other at the outlet. The mean real residence time ( ) was calculated and it was below the spatial time (τ) both in summer and winter. Sampling carried out in the outlet flow along the time allowed the application of population balance models and to analyze the existence of short circuits and dead spaces. The pond active volume was calculated, being 70 and 22% of total volume in winter and summer, respectively. In both seasons, the active zone showed a hydrodynamic behaviour similar to the completely mixed continuous tank reactor (observed in the curves C and in the fitting of the experimental data at outlet and the use of the combined model of Cholette and Cloutier). From the experimental data of the remaining BOD5 it was possible to calculate the global kinetic constants for organic matter degradation and, from this, the constants at 20°C obtained at the most unfavourable (higher) water temperature observed. Both in winter and summer constants values (k20 = 0.46 and 0.32 d−1) seemed to point to the active zone of the system, showing a fundamentally aerobic behaviour.