Streeter-Phelps: Model the DO in a stream after adding waste water discharge

Developed a relationship to predict longitudinal oxygen profile in flowing waters as a function of:Strength of degradable organic matter (Mix of background BOD in stream and BOD introduced by a waste discharge)
--> slow decrease in O2

- Reaeration: Rate of diffusion of oxygen into the water from the atmosphere, proportional to the concentration deficit

“The rate of biochemical oxidation of organic matter is proportional to the remaining concentration of unoxidized substance, measured in terms of oxidizability.”

Calculation of BOD in stream after mixing with discharge:

Model Assumptions:
- Stream behaves as an ideal plug flow reactor (PFR)
- Flow rate, stream cross section and longitudinal velocity are constant
- Physical, chemical, and biochemical reactions of interest are BOD exertion and O2 transfer across air‐water interface

Model Limitations:
- only one sink for DO considered
- only one source for DO considered
- downstream movement by advection only
- Velocity, depth, BOD exertion, and reaeration are invariant with distance

Diskussion