Evoqua WALLACE & TIERNAN DEOX/2000, Instruction Manual

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75 W3T331759 / WT.050.585.003.UE.IM.1014
MICRO/2000® AND DEOX/2000® MODULE
4.1 Residual Form
4.1.1 Chlorine dioxide and potassium permanganate monitoring
The stability of the sample pH is not as critical when monitoring chlorine
dioxide and potassium permanganate residuals as when measuring chlorine
residuals. A sample pH change of 0.2 pH units between calibration will
cause less than 5% error. Response to chlorine dioxide is somewhat
improved at lower pH, however, and for best accuracy (stability) in the
monitoring of both residuals, carbon dioxide gas buffering of the analyser
sample is recommended. Carbon dioxide will also help prevent deposits
caused by water hardness within the wetted analyser components.
4.1.2 Bromine residual monitoring
Bromine residuals are often encountered in chlorinated water with a
significant bromide residual (e.g. in saline waters). Bromine residual
behaves very similarly to chlorine residual and so the application
recommendations for each are the same.
4.1.3 Chlorine residual monitoring
For the purpose of this description, chlorine species can be grouped as
follows:
a. Free chlorine - hypochlorous acid and hypochlorite ion
b. Chloramines - monochloromine and dichloramine
c. Organic chlorine - a broad group of compounds with relatively
weak disinfecting and oxidizing potential, a byproduct of
chlorination
d. Total chlorine - the sum of the above residuals
4.1.4 Free chlorine monitoring
In applications where the pH is less than pH8 an is stable, free chlorine
residual can be monitored with no chemical conditioning. Often the
stability of the water sample pH is not certain and a buffer is used to
regulate the analyser sample pH of between pH6 and pH4. If it is important
that the analyser function accurately under conditions where the pH of
the water sampled may vary, buffering is recommended.