Loss of Chlorine Effectiveness with pH Rise

Estimates the percent drop in biocidal effectiveness when operating pH increases, attributing the change to the shrinking HOCl fraction rather than to any change in chlorine feed rate.

$$\text{Effectiveness loss}=\left(1-\frac{f_{\mathrm{HOCl}}({\mathrm{pH}}_2)}{f_{\mathrm{HOCl}}({\mathrm{pH}}_1)}\right)\times 100\%$$

Variables

Symbol	Meaning	Unit
$f_{H}OCl(pH1)$	HOCl fraction at the starting pH	dimensionless
$f_{H}OCl(pH2)$	HOCl fraction at the higher pH	dimensionless

Worked example

From pH 7.5 (about 50 percent HOCl) to pH 8.5 (about 8 percent HOCl): loss = (1 - 8/50) times 100 = about 84 percent, consistent with the chapter statement of roughly 85 percent lost.

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Part of The Blueprint of Water