Most Rapid BOD Assimilation in Ganga and Yamuna Rivers

During a water quality survey of the Ganga and Yamuna of the Indogangetic plain, the assimilation of biochemical oxygen demand (BOD) after the waste outfalls at the urban centers along these rivers was found to be exceedingly fast. During the two‐stage BOD removal in these streams, the early reaches resulted from bioflocculation of waste colloidal matter with river water. It was found to follow a straight line law approximating a BOD rate constant (k) of as high values as 30 to 100day-1 (base e) resulting in about 60% BOD removal in 30 min‐60 min. In the later reaches, the BOD removal was found to follow the usual first order kinetics with k ranging from 1.5 to 5.5day-1 (base e) which are higher by an order of magnitude than the usual range of 0.2 to 0.5day-1 (base e). The dissolved oxygen (DO), which dropped to low values after the waste outfalls, was also found to recover in short times showing extremely fast reaeration. Such BOD exertion and reaeration have been modelled. The integrated effect of several drains releasing at an urban center has also been included in the prediction of BOD and DO.