Assessing oxidation pond design criteria in a tropical town with low water availability

Abstract

The waste stabilization pond system of Brazlandia consists of two series of anaerobic and facultative ponds running to parallel. Due to the low water availability in the region and the growth of the population, the design conditions of hydraulic retention time and organic loading were strongly modified during the operational period. Assessing of nine years of operational data in comparison with the current design approaches showed that this situation has affected the anaerobic pond efficiency. However, despite what is found in the literature, the increase of anaerobic pond water temperature beyond 20°C was accompanied by decrease in COD removal efficiency. The longer retention times observed to the facultative ponds have favored the increase of algae concentration in the pond, which reduced the overall COD removal efficiency. However, when the filtered sample is taken into consideration, the values easily fit the empirical models proposed in the literature. No significant correlation was obtained between the complete mixing flow model and operational data, which suggests that the reaction constant K is not so constant. In addition to dependence on temperature, Kfilt values showed a statistically significant correlation with applied COD load.