Continuously Stirred Tank Reactors (CSTR)
After a parcel of water enters the treatment measure, it begins to move towards the outlet. But even under ideal conditions (which are rare) it tends to spread out due to turbulence. This behaviour can be modelled quite closely by a series of well-mixed waterbodies notionally located within the physical storage.
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The cases considered above may be categorised into the following three groups:
i.good hydraulic efficiency with 
> 0.75;
ii.satisfactory hydraulic efficiency with 0.5 < < 0.75; and
iii.poor hydraulic efficiency where < 0.5.
Contaminant attenuation by the k-C* model is calculated separately at each timestep for each CSTR in a physical storage. As the assumed number of CSTRs in a storage increases the volume of each becomes less. Even so, the overall result is a greater change in pollutant concentration at the storage outlet.
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