Potable Water TreatmentBack
Potable water overview
It is no secret that this century will be characterized by serious problems related to water, which will compound the difficulties involving energy stemming from the last century. The scarcity of water in relation to demand will affect how this resource is used both for irrigation purposes and as drinking water, together with the water requirements of industry.
To remedy this, it will be necessary to develop effective technologies for the extraction of water (i.e. locating and drilling) and to streamline the delivery (from the source to the final consumer), but above all to maximize the exploitation (through recycling / purification of polluted water).
Water destined to human consumption must comply with the quality requirements of the governmental regulations. In particular, with respect to microbiological limits approximately 95% of the European water works provide a pre/post-disinfection phase. In Italy, in terms of volumes of drinking water supply (approximately 6 billion m3/year), it is believed that at least half the quantity is treated by chlorine dioxide in one of the production phases.
Chlorine Dioxide in potable water treatment
Chlorine dioxide may be used in the treatment of drinking water either as a disinfectant or as an oxidant.
As a disinfectant, it can be used in the pre-oxidation phase as well as in the post-disinfection phase. In the purification treatment of surface water, pre-oxidation is used to control the growth of bacteria and algae during the subsequent phases of the treatment. The use of chlorine dioxide in this phase, in place of chlorine/hypochlorite, has the advantage of considerably reducing the formation of halogenated organics (usually called Adsorbable Organic Halides or AOX), which, for water in distribution, must not exceed 100 mg/l according to many regulations.
The formation of THM (learn more to Health effects of Chlorine Dioxide and Chlorine) may occur more easily after treatment of surface waters containing high levels of organic precursors (with TOC - Total Organic Carbon – greater than 1 mg/l) but even with ground waters which are generally characterized by low TOC values (lower than 1 mg/l).
In sea-derived drinking waters, the formation of bromate ion (a suspected cancer promoter, Bromate) may occur for the chlorination of bromides naturally present in the seawater as dissolved salts.
Learn more to Health effects of Chlorine Dioxide and Chlorine
Furthermore, in the pre-oxidation phase chlorine dioxide oxidizes colloidal substances improving the coagulation process and, therefore, turbidity removal. In the post-disinfection phase, chlorine dioxide develops a dual action, bactericidal and virucidal in the form of ClO2, and bacteriostatic and weakly bactericidal in the form of chlorite (ClO2¯).
As a bactericidal agent it can remain active in water for at least 48 hours and its effectiveness is guaranteed for longer periods than that of chlorine. Thus, the use of chlorine dioxide in this phase can guarantee the inhibition of “bacterial regrowth” in the distribution network. Furthermore, in the presence of viral contamination, the virucidal and sporicidal powers of ClO2 are better than those of Cl2.