The City of Kalama’s diatomaceous earth water filtration plant uses a highly automated process that reduces lifetime costs and frees staff for other duties.
What the City of Kalama spent on its diatomaceous earth (DE) water filtration plant in 2002 has been more than made up for in operational savings since then. Reason? The plant essentially runs by itself, allowing Kelly Rasmussen and his staff of four to concentrate on their many other public works duties.
“If you’re looking for good water filtration, this is it,” says Rasmussen, public works superintendent for this Washington city of 3,900. “It’s not cheap but it’s efficient and pretty simple.” Simple enough so that Rasmussen can watch the plant on a SCADA system at his office five miles away and rest assured that if the produced water is off-spec, the plant automatically goes into the waste operation mode until the water quality clears up. Then it switches back to the filter mode.
And it’s not just the automatic operation that pleases Rasmussen. “It also met our requirements for installation of a water treatment facility in a very tight footprint,” he says. “The DE filter has allowed us to get to where we want to be.”
Adds Mike Johnson of the engineering firm Gray & Osborne, who designed the plant: “It was important for Kalama that they could use their existing staff, at the existing certification level, without having to add people to run the plant. It’s a mechanical operation, rather than chemical.”
Kalama sits on the banks of the Columbia River, 45 miles from its mouth at the Pacific Ocean, and about 40 miles north of Portland, Ore. In addition to residential and commercial customers using the water, the town has one of the larger ports of entry on the West Coast, and is the site of two large grain processors, several chemical plants, lumber and steel operations, and recently, a wine bottle manufacturer.
These industrial operations use just over half the water produced. “We also serve water well beyond our city limits,” Rasmussen says. “It’s very rocky terrain here next to the river, and it’s very hard to find good water in wells. A lot of our customers are outside the city.”
The area’s mountainous topography also affects the water system: There are 10 booster stations, 13 storage reservoirs and 17 pressure reducing stations (equipped with CLA-VAL valves) along the 50 miles of water distribution lines.
For many years, Kalama was served by a simple pump-and-disinfect water supply system, which drew water from the Ranney well alongside the Kalama River. The water was chlorinated, fluoridated and pumped to customers. However, in 1998, the state Department of Health ruled that the well was “groundwater under the influence of surface water,” and ordered the water to receive filtration along with disinfection.
“The Kalama River is a very pristine stream,” explains Rasmussen. “It comes down from Mount St. Helens. No dams interrupt its flow. Yet, the state determined that we were not drawing from a true aquifer, but rather that surface water was actually filling the collector laterals. There was concern for Giardia and Cryptosporidium. Chlorine does not kill hard-cell microbes like those.”
Working with the Gray & Osborne staff, the city conducted a pilot study of a diatomaceous earth filtration system supplied by Separmatic. “The test trailer was here for a lengthy pilot run,” says Rasmussen. “We obtained good treatment from it and decided to go with the DE filter.”
The new plant, opened in 2002, is built on the edge of a floodplain, so to save space, the facility sits on top of its 75,000-gallon chlorine contact chamber. During operation, well water is pumped from the Ranney to the DE filter and is pulled through 36 individual filter septums coated with DE. Next come disinfection with sodium hypochlorite and pH adjustment with sodium hydroxide. The water then goes through a static mixer and into the contact chamber.
Rasmussen explains the DE filter operation: “First we fill the filter tank three-quarters full with water, covering the septums. Then we add 200 pounds of DE to the precoat tank and fill that with water. An SPX - Lightnin brand mixer mixes the precoat slurry, which we then transfer to the filter via a Max-E-Glas transfer pump [Pentair Water/STA-RITE].”
At that point, the filter control is put into hand mode, and the filter pump recirculates the slurry slowly so that it builds a cake layer on the septums. Once the turbidity in the filter drops to an acceptable level (Hach turbidity meters), the control is put in automatic mode and begins to filter water, filling the 2-million-gallon finished-water reservoir. When the reservoir is full, the finished-water pumps turn off, allowing the filter pumps to simply continue to recirculate the water through the filter, keeping the filter cake in place on the surface of the septums.
“The water is sucked through the filter — it’s like a swimming pool filter on steroids,” says Rasmussen. “Any microbes become lodged in the DE media.” To backwash, the filter pump is turned off, a 6-inch drain at the bottom of the filter is opened, and the old DE cake is hosed off the septum. The residue and water pass to two 14,500-gallon deep backwash tanks outside the building. Supernatant is checked for pH and chlorine and, when acceptable, is released to the Kalama River.
The settled cake (about 80 cubic yards a year) is withdrawn from the tank bottoms every six months. A local farmer uses it in his tree-planting operation. “It works well,” says Rasmussen. “After all, it’s fossilized algae, full of nutrients.” The total time for backwashing and precoating a filter is about three hours.
Filter operation is not only straightforward, it is hands-free. “We send an operator out every morning to run the daily bench test, but the plant pretty much runs itself,” says Rasmussen. Using a WonderWare SCADA system (Invensys), integrated by Quality Controls Corp., Rasmussen can view the entire treatment sequence without leaving his office.
“When we selected the filtration system, we were looking for a plant that did not require a full-time operator,” he says. “We didn’t want to hire another full-time person to run the plant.”
Safety parameters are built in: The plant automatically shuts down and goes into recirculation mode if pH, chlorine or turbidity gets out of line. “The finished-water pumps will shut off, and the filter will go into a filter-to-waste mode, sending the water to our backwash basins until the problem is cleared up.”
The automation frees up Rasmussen’s small staff to manage many other duties, which include almost everything related to public works in Kalama: wastewater collections, street maintenance and parks, in addition to the water plant, meter reading and distribution line replacement. The team includes Chad Moon, field supervisor, and Travis VanSkike, Gary Griggs and Travis Buck, public works technicians. Rich Smith and Butch Owen are responsible for wastewater.
“We’re all certified operators and we’re all cross-trained,” says Rasmussen, who became superintendent in January 2012 and was the Evergreen Rural Washington State Water System Operator of the Year in 2010. “We do all mainline installations up to $65,000 in value and do our own sewer tie-ins and water service taps.”
It can be time-consuming, if for no other reason than the topography the team must deal with.
“The elevation here ranges from 20 feet above sea level to over 1,500 feet,” says Rasmussen. The hydraulic grade runs from 258 feet to 1,116 feet. That yields 17 different pressure zones and requires a battery of pressure reducing valves.
More work to come
And while Gray & Osborne’s Johnson explains that the produced water pumping system supplying the zones is designed to be as energy efficient as possible, the number of valves can be problematic: They require significant maintenance.
The demands on the multitasking Kalama staff could increase in the near future. Rasmussen says the economic meltdown of a few years ago dramatically slowed the area’s residential and industrial development, but activity is picking up again. “We can add a third filtration module if necessary,” he says. “It’s expandable.”
If that happens, the decision to invest in an automated treatment plant will be justified even further.