Sodium Dichloroisocyanurate Tablets for Household Drinking Water Treatment

January 6, 2021

Disinfectant sodium dichloroisocyanurate sdic is the sodium salt of a chlorinated hydroxytriazine and is used as a source of free available chlorine, in the form of hypochlorous acid, for the disinfection of water. It is widely used as a stable source of chlorine for the disinfection of swimming pools and in the food industry. It is also used as a means of disinfecting drinking-water, primarily in emergencies, when it provides an easy-to-use source of free chlorine, and, more recently, as the form of chlorine for household point-of-use water treatment.

Advantages in Drinking Water Treatment

One of these household water treatment technologies is sodium dichloroisocyanurate (NaDCC) tablets, an alternative to sodium hypochlorite (NaOCl) solution, which is produced and distributed in many countries for water treatment. Both NaDCC tablets and NaOCl solution disinfect water by releasing free available chlorine in the form of hypochlorous acid, which is an effective microbicide against a wide range of bacteria, viruses, and parasites. Although NaOCl releases all its free available chlorine immediately, NaDCC releases half of its free available chlorine initially, leaving “reservoir chlorine” that is released once the original free available chlorine has been used up. NaDCC tablets’ reservoir chlorine may be especially advantageous when water is subject to high organic loads, as is common in resource-poor and remote settings.

NaDCC tablets, which have been used for emergency water treatment since the 1980s, were approved in 2004 for daily use as a drinking water disinfectant by the United States Environmental Protection Agency and World Health Organization.NaDCC tablets are lightweight, easily disseminated, and can be stored for over 5 years without losing efficacy. Results of field trials suggest that NaDCC tablets are acceptable and effective for water treatment; but no health impact data have been published. To assess the health impact of NaDCC tablets, we conducted a field trial in Tamale, Ghana between August and November 2006.

Treatment achievability

At very high chlorine doses (up to 10 mg/litre), the sodium cyanurate concentration would be below 11 mg/litre. In emergency situations, “topping up” might be done in an attempt to maintain a free chlorine residual, but this practice should be discouraged. In this case, it would be possible for the sodium cyanurate concentration to build up to undesirable levels. In such cases, it would be very desirable to monitor the concentration of sodium cyanurate.

Additional considerations

The controlling factors are the level of free chlorine and the residue of cyanuric acid, particularly if there is topping up of chlorine in a static system under emergency conditions. The concentration of free chlorine should normally be such that it should not give rise to unacceptable tastes and should not normally exceed the guideline value of 5 mg/litre for free chlorine. Sodium dichloroisocyanurate used for disinfecting drinking-water should be of adequate purity so that there is no increase in any inorganic or organic contaminants in the drinking-water.

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