The Verdigris Water Treatment Plant in Broken Arrow is one of the largest membrane plants in Oklahoma and the country. While the plant operators are happy with the plant and the water quality it produces, getting to that point has been a bumpy ride at times.

For years, the city purchased water from an outside authority, delivered through a 23-mile pipeline that was showing its age. In 2004, the city embarked on a seven-year project to study, approve, design and construct its own 20 mgd treatment plant. In April 2014, the new facility along the Verdigris River began delivering water to the city’s 100,000 residents.

The city chose low-pressure microfiltration (MF) membrane technology out of a desire to use fewer chemicals and in view of concern about changing regulations, especially for disinfection byproducts. While starting up any new plant can be challenging, the Verdigris team found it especially so.

Many operators had little to no water treatment experience, and the membrane technology thoroughly tested their mettle. An algae problem further complicated matters. The team persevered, and today the plant operates superbly, producing water with 0.013 to 0.015 NTU average turbidity and 2.6 to 3.0 mg/L average total organic carbon (TOC).

Choosing membranes

Since membrane filtration is fairly new for drinking water plants, and even more so in Oklahoma, the state required a pilot study at the Verdigris plant. The city evaluated systems from four vendors and ultimately chose a system from Pall Corporation using Microza UNA-620A membrane modules. “I visited three California plants with similar systems, and I liked what I saw,” says Jimmy Helms, plant manager.

The system consists of 10 membrane racks with 115 modules per rack. It is sized for 20 mgd (28 mgd in warm weather from higher flux through the membranes), expandable to 40 mgd. The hollow-fiber membranes remove contaminants by physical straining of particles larger than the 0.1-micron membrane pore size. Six 200 hp pumps push the water through the membranes, which are backflushed several times a day. Filtered solids are sent to three on-site lagoons.

Raw river water enters two intake screens (Concord Screen), is pumped via vertical turbine pumps through a 42-inch pipeline and enters one of two pre-sedimentation basins. Pretreatment basins with four parallel trains achieve rapid mix, flocculation and sedimentation. Aluminum chlorohydrate is added as a coagulant. Plate settlers (Jim Myers & Sons, Inc.) separate the solids and send clarified water to the membranes. 

After membrane treatment, the water is disinfected with sodium hypochlorite (MicrOclor generators, Process Solutions) then fed with chloramines as a secondary disinfectant. Fluoride is also added. The finished water is sent to a clearwell, and four 900 hp U.S. Motors vertical turbine pumps (Nidec Motor Corporation) deliver the water to the city’s distribution system. The entire treatment system is controlled and monitored with a SCADA system (Rockwell Automation).

Assembling the team

The plant has nine operators, most of whom were hired six months before the new facility came online. Eli Prock, assistant plant manager, started halfway through the construction process. “We initially had high turnover, as some found that water treatment wasn’t for them,” says Helms. “Eli came from 100 miles away and relocated in Broken Arrow. We were able to attract a few college graduates looking for jobs, and others were operators with past experience.”

The plant is in a rural area, so most of the staff commutes from Tulsa and other suburbs. Says Helms, “While staffing is not totally stable, it’s getting better. One operator retired, and a 13-year employee is leaving. So, we’re trying to institute an operator progression pay plan.” The plant pays for new operators to attain higher certifications. And while every operator must have at least a Class D license, new operators can work under supervision with a temporary license for a year until they can attend training.

As manager, Helms maintains morale by “giving ownership. We let them know that it’s their plant and so it’s up to them to make it run efficiently. We’ve been excited about this new plant from the beginning, and this carries over to new employees.”

The operations team handles everything, including laboratory testing, maintenance, cleaning, grounds maintenance, and repairing broken pipes and instrumentation. The plant is staffed around the clock. Each shift has two operators for safety reasons (one operator on weekends).

The team reports to Helms, who has been with the city for 33 years and holds Class A water operator certification. Besides Prock (Class B license), he supervises operators John A. Williams (Class B), Dewight Harp and Robert Sherman (Class C), Jed Beloncik, Michael Story and Jordan Wilson (Class D) and Richard Daniels and Blake Shepherd (temporary licenses).

Several operators also hold water laboratory, wastewater operator and wastewater laboratory licenses. Helms believes the operators’ greatest strength is their adaptability: “They realized very quickly that things don’t stay the same, and you have to adjust. I’m very impressed that they are able to figure out ways to overcome problems, even though they don’t all have a lot of experience.”

Learning the ropes

After almost a year and a half, Helms reports that the operations team members feel much more comfortable with the new equipment. On-site training sessions by vendors, with an overview of equipment operation and maintenance, helped the operators come up to speed. Plant staff videotaped the sessions for later review and to help train new team members as they come on board.

Operators had to learn two SCADA systems: one for the pumps, chemical dosing process and other systems, and one for the membrane system. “The SCADA was not one of the more difficult things to learn,” says Prock. “On all the equipment, we used the more experienced operators to help those with less experience, and that worked out well.”

The on-site hypochlorite generation process was not difficult for the operators to grasp and has been mostly problem-free. “It has a high capital cost, but a payback over a period of time,” says Helms. “We chose it because chlorine gas is becoming more regulated, and everyone is trying to get away from using it.”

The learning curve on the membrane system was steep. “The system has more of everything, both mechanically and electrically,” says Helms. “It’s like the difference between your old station wagon and a Formula One race car. It’s a high-performance machine.” Prock agrees: “There are a lot of things to tweak, like the clean-in-place cycle and the once-an-hour air scour and backwash.”

Taming the algae

If adjusting to new technology wasn’t enough, the Verdigris River threw the team a serious curveball in summer 2014. Algae growth in the river during that time limited water production at the plant. As the outside temperature rose, people began using more water, and an unusually large amount of algae from the river began clogging the plant’s membrane filters.

“If you look at a map of the river, you will see a navigational channel created for barge traffic,” says Helms. “They built a series of dams, and there are little S-curves, or oxbows as we call them, so there’s not much water flow. When we pull that water in, if conditions are just right, the algae growth explodes.”

Operators found that the normal three-and-a-half-hour membrane clean-in-place procedure was ineffective. With water consumption greater than the plant could produce, they couldn’t do a longer, more effective cleaning, which would have taken 13.5 hours. Since the plant was pumping treated water at a reduced capacity, the city asked residents to conserve water until the problem could be fixed.

The operations team solved the problem after a month by using pre-chlorination and a copper-based algaecide. Helms credits Prock with developing a short-term membrane cleaning protocol, with assistance from Pall. “We brought in a field technician from Pall to help us through the process, which involved adjusting air velocities for the air scour and a short clean-in-place until we could do a full-blown cleaning,” says Helms.

Broken membrane fibers posed another challenge. “We use feed water to backflush the membranes and then send air through them,” Prock says. “But because the membranes were packed with all the accumulated solids, the water and air stream caused broken fibers.” Operators had to remove modules from the rack and take them apart to repair the fibers, a time-consuming job.

“Unfortunately, there was no initial training on the membrane system that covered what to do if the membranes became clogged with algae,” says Helms. “It was a trial by fire, but also a learning experience that we will never forget.”

Future growth

The plant was designed for expansion, which Helms says will need to happen fairly soon to accommodate growth: “Broken Arrow is one of the few cities in the state that has experienced steady growth. We will probably need to double plant capacity in 10 years, which means we’ll need to start planning in five years.”

Helms also expects regulations to change: “Every five to six years, the EPA reviews a list of contaminants and finds new things to regulate. The next thing could be pharmaceuticals. So, we have to be prepared.”

Helms offers advice to other communities planning to build new facilities. “Knowing what I know now, my advice is to get new employees in place during the construction process,” he says. “Send them to similar plants so they can talk to the operators.” He suggests allowing them to take part in some of the equipment assembly: “If we could have had all our people in place, that would have been a good training tool.

“Our operators received some of the equipment training four months before plant startup. That needed to occur just before startup. The exception was a four-day class on the membrane system with a Pall instructor that was given closer to startup and taped by a professional videographer. At the end, the operators took a written exam and then received hands-on training. It was the only training done that way.”

Prock observes, “We received some of the training so far in advance that when it came time to operate that equipment, we were asking ourselves, ‘Where’s the on button?’”

Still, Helms is pleased with the way things turned out: “This $60 million membrane plant was built by our citizens to provide Broken Arrow with clean, safe potable water. The operators and I have not lost sight of the trust these citizens have given us. I am so proud of the way the operators have stepped up to make this facility a success.”