## Rate Of Kill

Figure 7.30.6 shows the rate of kill (microorganisms) for combined- and free-chlorine residuals. This curve is based on the rate of kill expressed in the following equation (unique for chlorine):

~dtT

where:

N = population of living microorganisms t = time k = rate constant

Integrating and converting to base 10 yields the following equation:

where:

N0 = initial population N1 = population at t1

Kill rates are usually measured in terms of coliform bacteria present. Figure 7.30.7 shows the relationship between coliform bacteria and chlorine residuals for sewage; Figure 7.30.8 shows the relationship between chlorine dosages and detention times.

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