Disinfection changeover at Missouri water plant

Disinfection changeover at Missouri water plant
The Maryville team includes, from left, public works director C.E. Goodall, operator Herman Crumb, operator Jonathan Eckstein, operator Willie Kort, lead operator Joe Finch, Southern Iowa/Missouri regional manager Steve Guthrie, operator Danne Lyddon, and operator Don McAdams. (Photo courtesy of Joe Finch)

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The Maryville (Mo.) Water Treatment Plant recently switched from free chlorine to chloramine disinfection to meet U.S. EPA Stage 2 Disinfectants and Disinfection Byproducts (DBP) Rule. The 5 mgd Maryville facility serves about 17,000 people between the city and the rural water district. 

Under the Stage 2 DBP Rule, concentrations of disinfection byproducts TTHM and HAA5 must be in compliance at individual distribution system locations. This differs from current requirements, which determine compliance from an average of samples from locations across the entire system.

“TTHM and HAA5 averages become locational averages, so we can’t use the whole system to average down a high number,” says Steve Guthrie, People Service Southern Iowa/Missouri regional manager, which operates the plant. “Each site has to stand on its own. We have a couple sites that once they are standing by themselves would not meet the new regulations.”

Built in 2001, the plant was designed for chloramine disinfection, so the changeover was essentially straightforward. “People Service began operating the plant in 2006 and was able to solve things chemically and meet current regulations without switching to chloramine,” says Guthrie.

“We did it that way until the Stage 2 rule was announced. After numerous attempts to stay with free chlorine, it was determined that the best option was to go to chloramine disinfection.”

Lead operator Joe Finch adds that the shift in operations did not involve extensive labor, but rather thorough inspection. “We had to go through everything to make sure it was operational because it was mothballed for 10 years,” he says. “There was a lot of prep work, and we had to verify we had our monitoring requirements right.”

People Service coincided the changeover with a systemwide hydrant flushing so the system could be turned over quickly.

In operation for a month, the plant has already seen advantages from the switch. “We’ve reduced costs because we don’t have to use as many pre-oxidizing chemicals,” says Guthrie. “We’re also looking at reducing coagulant doses a little bit because chloramines don’t form TTHMs. Previously, the clarification had to produce such a high quality of water to meet limits that it took a lot of chemicals.”

The disinfection process does not make the water harmful to people drinking or using it, but some residents had concerns about their aquariums. “Most of the questions received were from aquatic pet owners, because fish can absorb chloramines directly through their gills,” says Guthrie. “So owners have to make sure they dechlorinate their water properly to get rid of the chloramine.”

Water customers also benefit from the changeover. “We’re seeing improvements in taste and odor,” says Guthrie. When chloramine residuals are monitored correctly, taste and odor are similar to a free chlorine plant.

While the plant was designed to make the switch simple, Guthrie says the important aspect was ensuring that systems were operating correctly. “The preparation time in making sure we had the equipment working properly, the correct monitoring equipment, and the process control procedures in place comprised the bulk of the work,” he says. “The actual switchover was pretty easy. We’re confident in what we’ve done. We’ve had no issues.” 



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