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KMID : 0381319740130040001
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Korean Journal of Occupational Health
1974 Volume.13 No. 4 p.1 ~ p.5
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Determination of Chlorine Demand Using Residual-Dose Curve
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Abstract
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For a relatively pure water, the chlorine demand may be defined as the quantity of chlorine required to leave a specified residual after a specified contact time. It is usual to specify a free chlorine residual of 0.1-0.2㎎/ℓ after a contact of 30-60 minutes. This simple definition is likely to prove unsatisfactory for a more polluted water. In th s case the only satisfactory approach is to plot the curve of total residual against dose from zero to beyond the breakpoint. The contact period should be 60 minutes, and the chlorine demand may be defined as the dose required to give at least 0.1㎎/ℓ free chlorine residual at or just beyond the breakpoint.
The purposes of this experiment were:
(1) to plot the residual-dose curve for a polluted water and to specify the chlorine demand, and
(2) to introduce a more modern method for the determination of free and combined available chlorine in water using diethyl-p-phenylenediamine(DPD).
The following results were obtained:
(1) The DPD method could be carried out by titration method and showed sharper free and combined differentiation than the ortho-tolidine method.
(2) The initial pH values were in the range of 5.5-5.9 and, therefore, HOCI was assumed to predominate. The final pH values were in the range of 5.6-7.4 and OCI-was assumed to increase.
(3) The breakpoint occurred at 20㎎/ℓ chlorine dose and the CI-N ratio at this dose was 10. The monochloramine and dichloramine were produced until breakpoint, and dichloramine increased according to the increased CI-N ratio. After breakpoint, the trichloramine and free chlorine increased.
(4) The chlorine demand calculated was 16.7㎎/ℓ.
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