A Probabilistic Analysis of Dissolved Oxygen-Biochemical Oxygen Demand Relationship in Streams

Until recently, the classical Streeter Phelps equation (1) was used widely in predicting the response of dissolved oxygen deficit to organic waste loads discharged into a stream. However, the wide deviation of predicted values of oxygen deficit from the observed values led several investigators to modify the Streeter-Phelps formulation by taking into account other factors such as benthic demand, photosyn thesis, and algal respiration, in order to improve on the prediction techniques (1) (2) (3) (4). In the Streeter Phelps formulation and these other modified equations the reaction velocity coefficients affecting the rates of BOD removal, atmospheric reaeration, etc., are taken as constants, although it was recognized by a few investigators that the coefficients are far from being con stants (5) (6). These investigators postulated statistical models for pre dicting critical oxygen concentrations mainly to avoid the errors in the pre dictions due to the fluctuations in the values of deoxygenation and reaeration rate coefficients.