MODELS FOR POLLUTED STREAMS SUBJECT TO FAST PURIFICATION

The classic Streeter-Phelps models for stream analysis, though in use for the last five decades, are of little value for an accurate prediction of polluted streams' Biochemical Oxygen Demand (BOD) and Dissolved Oxygen (DO) sag parameters, because they do not account for bioflocculation taking place after the sewage outfalls into streams as a result of which, settleable BOD, a significant component of the total BOD, is removed in short distances. The extremely fast BOD assimilation in rivers Ganga and Yamuna of the Indogangetic plain modeled for the physico-chemical linear removal of the settleable BOD and exponential decay of the nonsettleable BOD, has been utilized for evolving models for accurate prediction of DO sag parameters and BOD in point and nonpoint systems of waste outfalls. Case examples have been presented for illustrating the computation of compound DO sags resulting from multi-waste outfalls, and to show the superiority of a point system over the nonpoint system of waste disposals.