Tastes Great!

Technology and teamwork help Moorhead Public Service deliver consistently high-quality water from a highly variable source in Minnesota’s Red River
Tastes Great!
Water plant supervisor Kris Knutson adjusts an ozone gas feed valve. Ozonation has helped Moorhead Public Service correct recurring odor issues caused by source water variation. (Gas flowmeter by ERDCO Engineering Corporation, valve by Modentic Industrial Corp.)

Interested in Instrumentation?

Get Instrumentation articles, news and videos right in your inbox! Sign up now.

Instrumentation + Get Alerts

The Red River is best known for periodic floods that afflict North Dakota, most notably around Grand Forks. Much farther south, in Moorhead, Minn., the river is known for something else, though mainly to the staff at the water treatment plant.

“Up here, it’s not a big river,” says treatment plant operator Dan Haman. “Local events can have a large impact on it. A rain event can often wash interesting water into the river, especially if the weather has been dry for a while.”

Years ago, that led to complaints from customers about odor and bad taste in the water coming from the tap. That no longer happens. In 1995, Moorhead Public Service added ozonation to its treatment process, and it proved to be a reliable cure. In fact, for the past two years, Moorhead’s water has been voted the best tasting in the state in a competition held by the Minnesota section of the American Water Works Association.

Troy Hall, Water Division manager, credits the treatment technology, along with a talented operations team, with keeping the process on track. “When we look at the SCADA and see our water-quality trends, we want to see flatlines — everything just humming along,” says Hall. “Through teamwork, that’s what we’ve accomplished.”

 

Variable source

What the Moorhead team calls the North Treatment Plant (10 mgd capacity) was built in 1995. The old 6 mgd treatment plant is now rarely used: The staff operates it periodically just to make sure it remains functional and available for emergencies. When the plant operates, it treats well water only.

The new plant, with 10 full-time and two part-time staff members, was designed specifically to deal with variable source water in the Red River. The utility also draws well water from the Buffalo Aquifer, but the river provides about 85 percent of the source water on an annual basis.

“There’s a reason it’s called the Red River,” says Nate Halbakken, lead treatment plant operator. Which is to say it’s not what one would call clean. The Red is subject to wide variations in organic matter and hardness, related to weather and the nature of the watershed, Hall observes. Normal flows range from about 3,000 to 5,500 cubic feet per second.

The main feeder streams include the Otter Tail River, with generally high water quality; the Bois de Sioux River, with very poor water quality; and the Wild Rice River. “Every river system that feeds the Red is variable, depending on how much rain we’re getting at the time,” says Hall.

At the old treatment plant, which used lime and soda ash softening and dual-media filtration, the wide source water variations overwhelmed the process. At the time, the source water included about 60 percent river and 40 percent well water. Potassium permanganate and sometimes activated carbon were fed at the river pumping station, but at times that wasn’t enough. When taste and odor problems arose, complaint calls came in bunches.

 

Reliable process

The MWH engineering firm (then known as Montgomery Watson) designed the new treatment plant. The Moorhead team has steadily improved on the design with instrumentation and updates to the SCADA system, originally supplied by Instrument Control Systems (ICS).

One river pump station and two well pump stations deliver raw water directly into the plant. The waters mix in an influent chamber, and the flow then enters two 5.5 mgd softening basins (Infilco Degremont). Typically, only one basin operates at a time, and when both operate, they work in parallel.

Water in the basins is fed with lime and soda ash, along with ferric sulfate as a coagulant and polymer for flocculation. Ammonia is also added in the softening stage for bromate control in the downstream ozonation process.

The WEDECO ozonation/recarbonation chamber (Xylem) has six cells fed with variable amounts of ozone and carbon dioxide, depending on raw water conditions. Residual ozone is sampled at various points in the chamber.

Before final filtration, fluoride is added, along with sodium hexametaphosphate for heavy metal sequestration and corrosion control. The plant’s four dual-media filter cells each hold two feet of anthracite coal atop 12 inches of sand. The filtered water goes to the clear well, where chlorine is fed to combine with ammonia and form chloramines for disinfectant residual. The water is then delivered to the reservoirs and water towers (7.9 million gallons total system storage).

 

Ozone does it

Hall notes that ozonation is the key to odor and taste control. “We ozonate at very high pH [at times 11 or higher] so that we benefit from some advanced oxidation,” he says. “Ozone has been a really big improvement since it came online in 1995. It helps break down the organic material. Sometimes we feed CO2 with the ozone as the pH is dropping down close to that of the product water. That helps with taste and odor, too.”

But it wasn’t technology alone that conquered the variability of Red River water. The plant staff’s diligence had a lot to do with it. “Since we started this plant, we have probably doubled or tripled the amount of online instrumentation,” says Hall. “Our SCADA gives us a lot of information about water quality and what’s happening in the process, and we’re constantly trying to improve that.”

The system’s programmable logic controllers and other control hardware are from Allen-Bradley (Rockwell Automation), and the SCADA software is from IntelliSys Inc. Online instrumentation in the treatment plant and water system includes:

• Three total chlorine analyzers from Wallace & Tiernan (Siemens Water Technologies Corp.)

• Monochloramine/ammonia analyzer, five pH monitors, and eight turbidimeters from Hach Company

• Two pH controllers (CO2 auto control), four ozone analyzers and two conductivity meters from Rosemount Analytical (Emerson Process Management)

• Organic online analyzer from s::can Measuring Systems

Benchtop lab equipment includes a turbidimeter and spectrophotometer from Hach Company, total organic carbon analyzer from OI Analytical, an IC chromatograph from Dionex, now sold as Thermo Scientific – Water Analysis, and an Orion pH meter from Thermo Scientific – Water Analysis.

The team tests raw water for hardness and alkalinity every four hours and tests the finished water every eight hours. The ozone analyzers test the water in the ozone contact chamber every 20 seconds. Ozone dosage is adjusted manually based on monitoring for ozone residual. “We have to adjust the ozone feed rate as water quality changes — on a good day, just a couple of times; on a bad day, once an hour or more,” says Haman.

The SCADA is programmed with the U.S. EPA ozone contact time (CT) requirements for disinfection. The ozone analyzers feed data directly into the SCADA, which calculates the actual CT value in real time. “In operations, we adjust the ozone, pH or whatever parameter is necessary to make sure the actual plant CT value is above the EPA requirements,” says Haman. “Once we meet the disinfection requirement, 99 percent of the time the odor and taste issues are taken care of.”

 

As a team

The staff’s success derives in part from the team atmosphere its leaders try to create. “There’s a lot of overlap in the way we do things — a lot of cross-training,” notes Kris Knutson, water plant supervisor. “We don’t like to keep secrets between positions. We expect all our operators to be very familiar with the SCADA. As a supervisor, I try to involve the operators so they can help me out with data analysis, maintenance tasks, or whatever happens to come up.”

Halbakken adds, “We communicate with each other. If one of us sees a problem, we alert the others. Everybody is always looking to keep the best product going out of the plant at all times. If that means someone has to be called at three in the morning to deal with a problem, everybody’s open to that. Everyone’s willing to help out.”

Notes Haman, “We try to work to each other’s strengths and shore up our weaknesses. For example, Nate is better at plumbing than I am, so I’ll give him plumbing jobs. In turn, he can give me data to analyze to find out when is the best time to order lime. We each have our little projects and our specialties.”

Hall cites SCADA work as an example of the team’s cooperation. “For the past decade, we have done all our SCADA work internally,” he says. “It’s not a perfect SCADA, but it has been built by people who really care about the end result. When we want to make a change in how a process works, we all work together.

“I’ve done some SCADA work in the office. Kris and Dan have done screen development for various purposes. It has evolved almost entirely in-house. We also select and install our own instrumentation.”

 

Problem solvers

Teamwork has helped the Moorhead staff resolve a variety of process issues. Several years ago, pH variability was a constant challenge. Working together, staff members made the correction by installing pH probes, making plumbing changes, and doing SCADA programming.

In another instance, rising non-carbonate hardness in the Red River was taking a toll on the soda ash feed pumps. A former operator located a peristaltic pump model (Watson-Marlow) that appeared better suited to the task. Operators, an instrument technician and electricians from the utility’s electrical side worked together to test and install the new pumps. “In a few months, we went from having to service the pumps every week to having almost no problems,” says Haman.

Another improvement involved installing a meter in the intake line to sample Red River water for conductivity as a way to predict total hardness in the river in real time. The team did the job, including data analysis and SCADA programming, entirely in-house, installing a used instrument purchased on the Internet for a few hundred dollars.

Future plans include installing instrumentation at the river pumping station, about three miles (two hours of in-pipe travel time) from the plant. “I’m excited about that,” says Haman. “We’ll be able to see changes in the water before it gets to the plant and so deal with them more effectively.”

Hall calls it a privilege to lead a staff with many and diverse talents. “The strengths of our people make it all work,” he says. “We try our best every day to use the strengths of the people we have.”

The results show up daily in the water glasses of Moorhead residents.



Discussion

Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.