How Chlorine Dioxide Used for Water Disinfection?

How Chlorine Dioxide Used for Water Disinfection?

Disinfection refers to the inactivation and/or destruction of pathogenic organisms in order to prevent the spread of waterborne diseases. Wastewater disinfection is practiced using many different means to improve water quality. Chlorine dioxide (ClO2) is another bactericide, equal to or greater than chlorine in disinfecting power. It is an effective disinfectant in both water and wastewater treatment systems.  

Chlorine dioxide is a neutral compound of chlorine, it disinfects by oxidation. It is a relatively small, volatile, and highly energetic molecule, and a free radical even while in dilute aqueous solutions. At high concentrations, it reacts violently with reducing agents. However, it is stable in dilute solution in a closed container in the absence of light. Chlorine dioxide is an unstable and explosive gas and for this reason, it must be generated on-site. Generation of chlorine dioxide involves reacting sodium chlorite (NaClO2) with chlorine to produce gaseous chlorine dioxide according to the following reaction:

2NaClO2 + Cl2 → 2ClO2 + 2NaCl

Recently, the production of chlorine dioxide from sodium chlorate (NaClO3) has been introduced as a generation method in which NaClO3 is reduced by a mixture of concentrated hydrogen peroxide (H2O2) and concentrated sulfuric acid (H2SO4).  

The active disinfecting agent in a chlorine dioxide system is free dissolved chlorine dioxide (ClO2). Chlorine dioxide has an extremely high oxidation potential which probably accounts for its potent germicidal powers. Possible bacteriocidal mechanisms may include inactivation of critical enzyme systems or disruption of protein synthesis.

An advantage of using chlorine dioxide is that it does not react with ammonia to form the potentially toxic chloramines. It also does not have a tendency to form trihalomethanes in water treatment distribution systems or wastewater treatment outfalls. The environmental impacts associated with the use of chlorine dioxide are less adverse than those associated with chlorination. However, dechlorination is required. Dechlorinating wastewater disinfected with chlorine dioxide can be achieved using sulfur dioxide.