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Chlorine Based Disinfection

Background

Chlorination is the most common means of disinfection applied in Australia due to ease of application and powerful oxidative ability. One disadvantage however, is that chlorine undergoes a variety of undesired side reactions with both organic and inorganic dissolved species that reduce its availability for disinfection purposes. This is also true, albeit to a lesser extent, for chloramination (the combination of chlorine and ammonia). For this reason, higher doses are applied at the treatment plant to ensure the water is microbiologically safe, even at the distant ends of the water distribution system. In order to determine this higher requirement, the chlorine 'demand' of the water must be known as well as the rate at which the chlorine concentration decays. The AWQC is equipped to carry out all chlorine related analysis according to standard approved methods.

Techniques

Free and total chlorine concentration

All chlorine species in potable waters can be determined by titration; this includes free chlorine and total chlorine as well as chloramine species ie. combined chlorine [monochloramine (NH2Cl), dichloramine (NHCl2), nitrogen trichloride (NCl3)] The method is applicable to concentrations, in terms of chlorine (Cl2) from 0.03 to 5 mg/L total chlorine (sum of free and combined chlorine) and at higher concentrations by dilution of samples.

Chlorine/Chloramine demand and simulated distribution system (SDS) analysis

Chlorine/Chloramine demand analysis determines the amount of disinfectant required to achieve a residual in a water sample by standard addition of chlorine (and ammonia for chloramines) with direct measurement using DPD/FAS titration. The chlorine/chloramine demand is determined as the difference between an initial chlorine dose and the chlorine residual after a set contact time, usually 30 minutes. Simulated distribution system testing usually operates over several days and aims to replicate and define the rate of decay of disinfectant residual as a result of organic and inorganic characteristics of the water. While the effects attributed to pipe wall effects are not accounted for, this can still give a reasonable estimate of the ability of disinfectants to penetrate into the distribution system and whether higher initial doses or downstream booster doses will be required as a result of changing treated water quality. These methods are applicable to all freshwaters, sea water and wastewater samples.