· To provide a
practical example of how to calculate chlorine demand in a water supply.
· To discuss and provide
practical examples of different methods of chlorine residual analysis, with an
emphasis on use of DPD tablets and comparators as a quick and reasonably
accurate method.
· To discuss why free chlorine
may be lost and the significance of high levels of combined
chlorine.
1. Make up a range of chlorine solutions using HTH
or chlorine tablets. It is suggested that 4-5 different concentrations of
chlorine solution are prepared.
2. Ask the participants to test the free and total chlorine
residual in each solution and calculate the combined chlorine (combined chlorine
= total residual - free residual).
3. Add contaminated water to solutions and ask the participants
to re-test chlorine residuals.
4. Discuss the results and the need for maintaining residuals
during distribution. Highlight the relative advantages and disadvantages of
different disinfectants using the disinfectant session notes.
5. Discuss the ways in which free residual may be lost and
highlight that highlight that high combined chlorine indicates sanitary
integrity of the system is
compromised.
