Behavior of thermal stratification in a facultative stabilization pond

Abstract

The thermal stratification in a pilot-scale facultative waste stabilization pond under tropical conditions was investigated in a study presented in this article. Temperature sensors were located at different depths inside, as well as outside of the pond, to measure the water-air temperature variations continuously at 30 minutes intervals for a period of four months, while the values of solar radiation, wind velocity and air temperature were recorded in a weather station in the same time interval. The results showed that the pond remained stratified for most of the time between 74.58% - 88.37% of the hours of each month calculated from hourly temperature measurements, and thermal stratification showed daily cyclic patterns with a stable thermocline located in the first 0.75 m depth. The wind and inflow rate conditions were not sufficient to homogenize the water mass temperatures and the destratification events in the pond were related to changes in air temperature. The results suggest that under tropical climates pond of small surface area with low wind conditions and depths greater than 1.50 m can remain stratified for long periods of time regardless of the season, cold or warm and that an outlet at a depth between 0.60 - 0.75 m could be enough to break the stratification and improve the quality of the effluent.