A small but dedicated operations team meets the challenges of learning to operate a new membrane plant treating seasonally variable source water
When Ray Pardee sees the award plaques on the walls at the Row River Water Treatment Plant, he feels pretty good.
That’s because the awards don’t just represent quality finished water, they document how far he and his staff — Steve Norman and Sam Haynes — have come in just a few years learning to operate what is essentially a brand-new facility, drawing from Oregon’s Row River.
It’s not just the new strainers and membranes, SCADA system and chemical feed apparatus. “This plant used to be seasonal, operating in support of the Layng Creek Water Plant,” says Pardee, plant superintendent. But in 2006, the city council decided to shut down the Layng Creek plant, rather than bear the expense of expanding it. That made the Row River plant the sole source of clean water for the community (population 9,900).
The decision meant Pardee’s team had to operate around the clock. “That was a big challenge for us,” he says. “Before, we were an on-demand plant used only in the summertime. There were hardly any changes in the quality of the raw water. It was very steady.”
But operating year-round has meant dealing with significant changes in the quality of the raw water. That in turn requires careful adjustments in the treatment processes.“In the winter, we get a lot of rain,” Pardee says. “The river runs through steep slopes, and the runoff increases the turbidity and organic content of our source water. The quality of our incoming water can change by the hour, even by the minute, calling for adjustments in oxidizers and coagulants — pretty much everything. We have our hands full in the winter.”
They’ve handled it well. The plant was recently named Small Facility Membrane Plant of the Year by the Northwest Membrane Operators Association. The operators have been recognized as outstanding performers by the Oregon Health Authority, and water from the system has earned second and third place finishes in Best Tasting Water Contests held by the Pacific North West Section AWWA, Cascade to Coast subsection.
The original Row River facility was built in 1993 as a 2 mgd multimedia filtration plant, supplementing the Layng Creek plant to meet system demand during the peak summer months. A static mixer was installed just after the chemical injection points for aluminum sulfate and a cationic polymer, but the process included no flocculation or sedimentation.
Seasonal potassium permanganate was used to oxidize manganese. Pre and post alkalinity and pH were adjusted using hydrated lime; gas chlorine provided disinfection. The plant was designed for expansion to 4 mgd and then to 6 mgd with little additional infrastructure.
The 2008 plant expansion was the result of a joint-venture design-build contract with Black & Veatch and Slayden Construction Group. The arrangement guaranteed a maximum price for the project, which expanded production capacity to 4 mgd. The original plant was designed for easy expansion by removing just one wall and widening the building by 35 feet, enough space for the new membrane system with extra room for additional membranes down the road.
To start the process, raw water is diverted from the river by gravity about 1,000 feet to the treatment plant’s hydraulic chemical mixing tank. Potassium permanganate and aluminum chlorohydrate are added to the raw water to oxidize and coagulate turbidity, manganese, dissolved organics and color.
The plant’s 100 hp Floway vertical turbine pumps (Weir Specialty Pumps (WEMCO)) then boost the treated water to the membrane system. Next, 300-micron self-cleaning pre-strainers (Amiad) filter any coarse debris out of the treated water before it enters the microfiltration membrane modules. As the filtrate leaves the modules, a 12.5 percent solution of sodium hypochlorite is added for disinfection. The last step is the addition of hydrated lime for corrosion control treatment.
Treated water is then pumped to two side-by-side finished-water storage tanks (total 4.3 million gallons) at a high elevation in the city. These tanks provide the chlorine contact time needed to complete disinfection. “The water then gravity-feeds out of the tanks to meet distribution system demands,” Pardee says.
“The old diaphragm chemical feed pumps were replaced with peristaltic feed pumps. Additionally, new chemical feed injection points were installed to take advantage of available hydraulic mixing of the chemicals before the filtration process. We still have no need for flocculation or sedimentation.”
The new 4 mgd pressurized microfiltration membrane system (Pall Water) consists of two filtration racks, each containing 89 low-pressure filtration modules. “Each rack can produce 2 mgd of finished drinking water at all times regardless of the operating conditions,” reports Pardee.
The improvements added SCADA and radio communications to satellite sites. “These two items were a first ever for our water treatment plant,” says Pardee. “The old system was manually started and stopped each day by the operators and used on-site sensors, circular chart recorders and telephone auto dialers for alarm notifications.”
A new 8 mgd raw water riverbank diversion structure was also part of the renewal; the old one dated back to 1993. A new controls building at the river intake site houses an air compressor, air receiver storage tank, programmable logic controller and radio equipment. Security fencing protects the intake and building from vandalism.
The improvements took just under one year to construct. A major challenge was to keep the existing treatment plant in operation while the improvements were under construction. Once the expanded Row River plant was operational, Cottage Grove donated the Layng Creek plant and its transmission line to a newly formed water district nearby.
So how did the Row River team figure out the new processes and new operational procedures?
“We had cut our teeth on manual plants,” says Pardee. “In the old days, operators could see the treatment effects in the basins, and manually start and stop the system each day as needed.
“This plant was different. There was no standing over the basin to see what the water was doing. We had to use computer technology to see what was happening in the membrane modules. There were new chemicals and chemical addition. We had to learn the cleaning cycles for the strainers and membranes. Much of our training was simply hands-on and trial and error. It was a lot of supporting one another.”
While the staff received training from the manufacturers and had some help from local tech and engineering sources, most of the new know-how came from jar tests and observation.
“We optimized treatment through jar tests,” says operator Norman. “We use potassium permanganate as an oxidizer of manganese and dissolved organics because it doesn’t form a disinfection byproduct later on. We rely on our streaming current monitor (Chemtrac) to keep track of the residual in the feedwater and let us know if we’re overdosing.”
When the plant was first proposed, the staff was told coagulant chemicals weren’t needed for the membrane to produce good-quality finished water. “The thinking was that turbidity couldn’t pass through the membrane, but we neglected to realize that anything that was dissolved might pass through,” operator Haynes says.
When the membranes started up in summer, the finished water had very low turbidity. “But in the fall, with leaves and organics in the raw water, we couldn’t maintain a chlorine residual,” Haynes says. “Even with a high chlorine demand, we weren’t removing dissolved organics and metals.”
The team had to add coagulants in fall and winter, and now adds coagulants year-round. “Originally, aluminum sulfate was used for coagulation, but this was later changed to aluminum chlorohydrate, which reacts much faster in colder water,” Haynes says.
The team’s other challenges included dealing with mechanical issues like shear pin breaks on the strainers, controlling algae in summer and high turbidity in winter, and keeping the screens from plugging before the scheduled wash cycle.
The operators use various procedures to maintain the strainers and membrane modules. The pre-strainers complete a self-cleaning function about every half-hour and an air scrub backwash hourly. The membranes receive an enhanced flux maintenance procedure once a week, using a heated chlorine solution.
About every two months, contaminants that could cause fouling are removed from the membranes by circulating a heated chlorine-caustic solution for two hours, followed by a heated citric acid solution for one hour.
The operators perform a special lower header feed pipe manual flushing procedure before each clean-in-place. “This is to help keep the membrane modules from becoming plugged with fine silt, which occurs at times,” Pardee says. “We gently thump the module casing and listen to the sound it makes to determine if plugging is occurring. Another useful tool is to use a temperature gun during the circulation of the heated cleaning chemicals to ensure that no plugging is occurring anywhere within the modules.”
The new SCADA system created another learning curve, says Pardee. “We’re a little older and are just really getting into computers,” says Pardee. It has taken a while for the staff to master the different computer programs, the individual components of the system, and how to use trend charts to the best advantage.
“We’ve received some help from the city’s automation team, and we’ve used The Automation Group (TAG) out of Eugene on occasion as an outside contractor,” Pardee says.
The modernized plant went online in July 2008, and it took a more than two years for the staff to get up to speed on all the improvements and seasonal treatment challenges.
“When I first started, I had a full head of black hair.” Pardee says. “Now I have a few gray ones.” But the hard work and experimentation have paid off handsomely. The Row River plant is producing excellent-quality water regardless of the season or the weather.
Protecting the fish
The Row River is a favorite among sport anglers, especially for salmon and trout. The new diversion structure for the Row River Water Treatment Plant includes screens designed to keep fish from swimming into or being sucked into the intake pipe. The previous intake, built in 1993, also had fish screens.
The flat-panel intake screens (Hendrick Screens) have two side-by-side panels, each 8 feet wide (16 feet combined width) by 3.5 feet tall, installed at a 30-degree angle. While the screens are engineered so that the velocity of the water across them provides self-cleaning, the system also has an air-burst system.
“In the event that snails, algae blooms, sticks or leaves plug up the flow, the air-burst system is activated and clears the screen,” says Ray Pardee, plant superintendent. A control building at the intake site houses an air compressor that fills a 620-gallon air receiver tank, storing the compressed air. It takes about 30 minutes for the air compressor to recharge the air receiver tank to the 150 psi setpoint to be ready for another air-burst process.
Controlled by a PLC, the air-burst cycle can be initiated by a timer setting, water level differential, or manually by the operator. “There are external and internal level sensors that simultaneously monitor water levels on either side of the screen,” Pardee says. A level differential operator programmable setpoint in the PLC activates the air-burst system if the screen is becoming blocked by debris.”