Residual maintenance and DBP reduction in a distribution system with long detention times

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Courtesy of MIOX Corporation

The Cedar Knox Rural Water Project, in Northern Cedar and Knox counties, Nebraska, needed to reduce the formation of Total Trihalomethanes (TTHMs) while maintaining a chlorine residual at the farthest reaches of the distribution system. The water project serves four communities and 721 hookups with a total of 3,200 customers in Northeast Nebraska. The source for drinking water is the Lewis and Clark Lake, fed by the Missouri and Niobrara Rivers. Average winter flow is 300,000 gallons per day (GPD) with flows peaking at 750,000 GPD in the summer.

Cedar Knox traditionally treated the water with 150-pound chlorine gas cylinders, utilizing a maximum of about 25 pounds per day of chlorine. In the past, operators had to load the chlorine gas into their trucks and transport it to the water plant since the chlorine delivery truck could not access the plant. The disinfectant is injected prior to the clearwell and has about 6 to 8 hours of detention time before going out to distribution. The distribution system covers 360 miles of pipelines with the longest reach being 43 miles from the treatment plant. The water frequently has a 6-7 week detention time in winter with an additional 3-4 weeks of detention in the village of Obert, Nebraska, which is the farthest customer from the plant.

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