Use of chlorine dioxide to remove fish pathogens from garrison diversion water

This report considers the use of chlorine dioxide as an alternate disinfectant for the removal of biota from Garrison Diversion water. Laboratory testing has shown that chlorine may not be an acceptable disinfectant because it can produce carcinogens from side reactions with constituents found in natural surface waters.This study used Lake Sakakawea water collected at the Snake Creek Pumping Station located on the eastern shore. Water samples were of direct filtration effluent from a laboratory scale filter column. samples were gathered at several different turbidity levels. The "DPD" method, as published in "Standard Methods for the Analysis of Water and Wastewater," was used to measure the residuals of chlorine dioxide after dosing the samples and allowing a contact time of 10 minutes.The data was graphed using a spreadsheet and tables were used to determine dosages required for the various turbidity levels treated. Aliquots of samples were plated and incubated to determine effects of disinfection. All procedures were followed as out-lined in "Standard Methods for the Analysis of Waters and Wastewaters."Chlorine dioxide will produce a residual concentration of chlorine species in the dosed sample. This residual usually consists for the most part of unreacted chlorine dioxide, which is called a free residual. The results of this study indicate that chlorine dioxide is an effective means of removing pathogenic bacteria and viruses from Garrison Diversion water when disinfection is carried out under the standard conditions used in the laboratory and with a 10 minute contact time.The cost of the treatment has been estimated using conventional municipal drinking water process trains. Cost of treatment varies indirectly with treatment plant capacity. A treatment plant for domestic water supply is a good example of return to scale, to use a term from economics.The cost of using chlorine dioxide as a disinfectant is on parity with other chemicals such as chlorine, chloramine and other chlorine-based dosing additives when used in a large treatment system such as Garrison Diversion would require.More research is needed to determine the medical effects of such disinfectant byproducts as chlorite and chlorate. These byproducts are invariably present when dosing water with chlorine dioxide, though not always detectable.