Dissolved oxygen sag analysis for a settling fields overlapping type multi-wastewater-outfall

The classical Streeter–Phelps models for Dissolved oxygen (DO) sag do not account for a significantly settleable portion (about 10% in treated to about 60% in the untreated wastewater discharged) of the total biochemical oxygen demand (BOD) inputs into rivers through wastewater outfalls, and therefore, they can not be used to predict the DO sag to any accuracy and rationality. The author’s rationally composited model for an accurate prediction of stream BOD, accounting for near linear removal of settleable BOD as well as simultaneous exponential decay of the non-settleable BOD, is used to predict the DO sag resulting from a multi-wastewater-outfall system, wherein the settling fields of some of the outfalls interfere and overlap. An illustrative case example has been presented to demonstrate use of the models evolved under varying locations of the multi-wastewater-outfalls. A universal and integrated PC based computer program can also be evolved for the computation of the overall resultant DO sag to confirm the manually computed DO sag.