Sewage discharge and water self-decay: Streeter and Phelps model application

Due to the high waste deposition in superficial water, studies are necessary to emphasize the importance to monitor and apply tools, such as mathematical modelling. In this study, we used the classic Streeter and Phelps model to simulate the travel time necessary to depurate organic matter in the Tatu stream, at Limeira, São Paulo, Brazil, and to simulate the point-to-point depuration of organic matter in comparison to point-to-point empirical analysis. According to the simulations, organic matter would be established to 10 mg/L ${\text{O}}_2$ in few hours of time course of water without discharges in the stream, having the watercourse self-decay capacity. In addition, the analysis indicates that possible launches are being carried out along the stream, because, at the collection points, the obtained results presented higher biochemical oxygen demand than the expected for organic matter depuration, which denote discharges occurrences. Thus, this study emphasizes the relevance of monitoring actions and puts the model as a suitable tool to identify discharge sources in water.