Explain Chlorine Residuals
Free Chlorine Residuals: Cl2, HOCl, OCl-
Combined Chlorine Residuals: Chloramines (mono, di and tri chloramines)
The disinfecting ability of chloramines is much lower than that of free chlorine.
Satisfactory results can be obtained if a free chlorine residual of 0.2 to 0.5 mg/L can be maintained in the distribution system. Also if approved by health authorities combined chlorine residuals in the range of 1 to 2 mg/L should maintained at distant points in the distribution system.
Trihalomethanes (the following) which are formed as a result of chlorination are harmful and this must be avoided.
CHCl3 trichloromethane (chloroform)
CHBrCl2 bromodichloromethane
CHBr2Cl dibromochloromethane
CHBr3 tribromomethane (bromoform)