AWWA ACE93161

This paper describes the results of a monitoring program for chlorite and chlorate. The researchers investigated: the removal of chlorite and chlorate during artificial recharge; the development of an improved analytical method with ion chromatography; and execution of a monitoring program. This paper describes the results of the last three items, with emphasis on the monitoring program. Ten drinking water plants and three raw-water sources were monitored. Results from a number of plants (two each of surface water with storage reservoirs, surface water with artificial recharge, and a number with bank filtration from rivers) are summarized. Chlorite and chlorate were removed during dune filtration, at least to a few ug/L. Researchers concluded that chlorine dioxide may be used for disinfection, at least in the distribution system. However, in the course of the research, the view on chlorite and chlorate changed from that they were byproducts of chlorine dioxide to the view that they were environmental pollutants. This study shows that chlorate and chlorite are present as industrial pollutants in surface water. The only way to remove these products seems to be infiltration in anaerobic soil layers, although chlorite can be biodegraded partly under aerobic conditions. At present, chlorate and chlorite are more important as environmental pollutants than as disinfection byproducts of chlorine dioxide. The fact that chlorate can be found in drinking water after the use of sodium hypochlorite makes it important to look for alternatives.