Illinois Administrative Code
Title 35 - ENVIRONMENTAL PROTECTION
Part 378 - EFFLUENT DISINFECTION EXEMPTIONS
Subpart C - FECAL COLIFORM DIE-OFF MODEL
Appendix A - First Order Die-off Equation

Universal Citation: 35 IL Admin Code ยง A
Current through Register Vol. 48, No. 38, September 20, 2024

The first order die-off equation provides a method of estimating fecal coliform die-off in a receiving water as a function of time:

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Definition and discussion of terms:

Nt is the predicted concentration of fecal coliform at travel time t downstream; units = #/100 ml.

Nu is the fecal coliform concentration upstream of the source being modeled; units = #/100 ml.

This term will often be negligible relative to the contribution of the source.

No is the fecal coliform concentration in the effluent of the source; units = #/100 ml.

d is the ratio of the receiving water discharge directly upstream of the source to the discharge of the source; no units.

k is the first order die-off rate constant; units = 1/hours. The value of

k can vary as a function of receiving water characteristics, including temperature, exposure to sunlight, and turbidity.

t is the travel time to the point of interest below the source; units = hours.

e = 2.718

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