USING REDUCING AGENTS TO ELIMINATE CHLORINE DIOXIDE AND CHLORITE ION RESIDUALS IN DRINKING-WATER

In an effort to determine the viability of various disinfection alternatives, the Evansville, Ind., Water and Sewer Utility is engaged in a pilot-plant investigation to compare chlorine dioxide and ozone pretreatment. As a result of increased speculation that the total residual concentration of chlorine dioxide and its inorganic species will soon be regulated, supplemental studies were performed to determine the effectiveness of various reducing agents for reducing or eliminating chlorine dioxide and chlorite ion residuals in finished water. The effectiveness of ferrous iron in achieving the desired reductions is examined along with promising results obtained with sodium thiosulfate. Specific difficulties encountered with the sulfur dioxide-sulfite ion method of chlorite ion reduction are also presented.