Minimization of disinfection by-products formation in water purification process using chlorine dioxide : Case studies

The formation of the by-product chlorite after using chlorine dioxide for the disinfection of drinking water depends on the quantity of the organic matter dissolved in the water. A further decisive factor for the chlorite formation is the level of residual free chlorine dioxide. The chlorine dioxide demand decreases by application of activated carbon filtration, especially after the use of a combination of ozone and activated carbon treatment of the water. Nevertheless, higher chlorine dioxide residuals are a source of chlorite and chlorate formation. The concept of the "Minimum Chlorine Dioxide Dosage (MCDD)" is developed in order to give a clue to the water companies for an optimized chlorine dioxide dose without compromising the disinfection efficiency. By applicati- on of the MCDD, the residual level of chlorine dioxide is focused to 0.05 mg/L after 0.5 h contact time. In the range of the MCDD the ratio of the chlorite formation and the chlorine dioxide demand is nearly independent of the level of DOC.