Few clean-water plants are part of the local high school’s science curriculum.

But in Coeur d’Alene, Idaho, an advanced treatment facility that came online as one of the first secondary plants in the nation, hosts student tours as part of the high school science requirements.

Students get a close look at sophisticated processes designed to meet some of the most stringent ammonia and phosphorus removal standards in the country. And they are welcomed to the facility by William D. Hatfield Award winner Casey Fisher, chief plant operator, and a staff of knowledgeable, experienced operators Fisher describes as “dedicated to what they’re doing.”

Jamie Esler, who teaches environmental science at Lake City High School, says the tours show students how a variety of sciences are applied to benefit the area’s water quality. “Environmental science includes chemistry, biology, applied mathematics, public health and more,” he says. “Our students get to see how they work together. They especially like the lab, where they can see ciliates and rotifers up close on flat-screen monitors.”

A developing plant

The Coeur d’Alene treatment plant dates to 1939 and has served its community with secondary treatment since long before the 1972 Clean Water Act. Design flow is 6 mgd, and average daily flow is 3.6 mgd. The plant has undergone a continuous series of upgrades over the last four decades. “I’ve been here 36 years and I don’t think there are more than five where we weren’t under some kind of construction,” Fisher says.

At the head of the plant, centrifugal influent pumps (Flowserve) bring wastewater to quarter-inch mechanical bar screens (Headworks), cyclone grit pumps and aerated grit removal. After flow measurement and sampling, wastewater settles in three circular covered primary clarifiers. Both primary and secondary clarifiers have WEMCO drives (Trillium).

A pair of high-rate trickling filters, filled with plastic media and installed in 1996, provide the first phase of biological treatment. They replaced old rock filters. Next, the flow passes through a solids contact tank, which Sulzer turbo-compressors provides, and is equipped with Sanitaire fine bubble diffusers and ABS submersible pumps (Sulzer Pumps Solutions).

Treated water settles in three circular secondary clarifiers. A ZeeWeed membrane filters system (SUEZ Water Technologies & Solutions) provides tertiary treatment. With a pore size of 0.04 microns and six cassettes per train, the membranes achieve significant phosphorus reduction and aid in ammonia removal.

“We do remove some ammonia in our secondary solids return basins, but the amounts are pretty small,” Fisher says. “Most of our ammonia removal is in our tertiary membrane facility and our three chemical mix tanks, where we maintain a mixed liquor of around 5,000 mg/L and a solids retention time of 18 days.”

Amiad strainers are positioned ahead of the membranes, and plant staff members use citric acid and bleach to clean the membranes. A ChemScan UV analyzer measures orthophosphate, ammonia, nitrate and nitrite into and out of the tertiary system.

Dual disinfection

An in-vessel UV disinfection system (Wedeco) treats 1 mgd of nonpotable water used for irrigation, plant processes including seal water and washdown. Chlorine disinfects the rest of the effluent, and sulfur dioxide dechlorinates it. Discharge is to the Spokane River, which flows out of Coeur d’Alene Lake near the plant outfall.

The plant’s Wonderware SCADA system (AVEVA) includes seven displays around the plant that enable operators to view the process and make changes as needed. The central PLC is in the operators’ control room. Operators also have a Surface Pro laptop they can take home to respond to alarm calls.

Primary biosolids are gravity thickened, and secondary biosolids are thickened on a rotary screen (FKC). Solids are mixed and fed to an anaerobic digester, and then to a PHOENIX belt press and an Alfa-Laval centrifuge for dewatering. Biogas fuels Cleaver-Brooks Model 4 water-tube boilers, which are to be replaced with a new Hurst Boiler Series 100 Firebox unit.

About 3,000 dry pounds of 25% solids cake per day is hauled to the city’s compost site. There the material is mixed with bark chips and cured in static piles for at least 30 days. The finished material, marketed as “Coeur d’Green,” is sold to landscapers as a soil amendment and used on city property, including lawns at the treatment plant.

Biofilters control odors at the compost site and at the treatment plant. Biogas is used to heat the digesters and generate hot water to heat the rest of the treatment plant. A Hurst dual-gas water heater will be installed soon.

The series of plant improvements hasn’t impaired operations, Fisher says. “We’ve been able to work around them pretty well, and we’ve had no violations during the construction projects. Sometimes it’s made things a bit harder, but overall, we’ve done well.”

Year after year

The plant has essentially undergone a complete overhaul during Fisher’s tenure. In the 1980s, new solids contact, digestion and dewatering facilities went into operation. The lab was expanded to house operations control and administration. The chlorine contact process, primary clarifiers and biosolids compost facility also underwent upgrades. Improvements were made to raw sewage pumping, pre-aeration, grit removal, sludge thickening and dechlorination.

In the 1990s, it was phosphorus control, new plastic media trickling filters, and new digesters, dewatering and odor control. In 2000, Coeur d’Alene began a partnership with the HDR Seattle office and made improvements to disinfection, aeration control and stormwater management. That was followed by a new headworks, the addition of the dewatering centrifuge, and covers for the clarifiers and digesters. A new lab and administration building were completed in 2011.

In that same year, facing new total maximum daily loading requirements for phosphorus, the plant began pilot testing membranes, a membrane bioreactor and upflow sand filters. After their selection, the tertiary membranes were scaled up to 1 mgd in 2013-14, and to 5 mgd in 2016-17. The staff is preparing for a new operations control building and another centrifuge to replace the existing belt press.

Expert staff

To make so many changes while staying in compliance requires a talented, dedicated staff. “We have a dedicated group here,” Fisher says, noting that everyone knows the entire operation and how the various processes fit together to create outstanding effluent. “It’s not like some places where staff members don’t seem to know much beyond what their own job description calls for.”

Working with Fisher are superintendent Mike Anderson; assistant superintendent Ben Martin; operators Mark Moore, Andy Williams, Michael Taylor, Andrew Ruiz, Dustin Stoneback and Travis Stepper; Nick Zito, electrician and SCADA technician; and Mike Zwieble and Aaron Camp, mechanics. Some team members have 20 or more years of service.

Coeur d’Alene emphasizes in-house as well as online training, certification and licensing; all such activities paid for by the utility. Fisher says interaction with professional associations is also critical to staff knowledge and success.

“There’s nothing like going to class and interacting with others,” he says. “I like to have our folks involved in both the Pacific Northwest Clean Water Association and the Northern Idaho State Operators Conference. We do as much as we can with those organizations.”

Nutrient challenges

The full capabilities of the Coeur d’Alene team were critical in the success of the phosphorus pilot project a few years ago. Fisher credits the staff with the ability to understand the three technologies that were tested. All were operated at 50,000 gpd and all met the needed phosphorus reductions “most of the time,” Fisher says.

“It was our first pilot project,” Fisher says. “We ran it for two years.” The membranes performed better and were a better fit for the plant’s small footprint: “A full-scale MBR would have taken up too much space.”

While the operators ran the pilot system and conducted the necessary testing, they also figured out that the membranes could remove ammonia was well as phosphorus. “In tertiary membrane filtration, there is a return activated sludge line between the membrane tank and the chemical mix tank,” Fisher explains. “That, plus the constant air scour, enables us to achieve nitrification, and we actually get more than we need to.”

Teamwork does it

Fisher credits his operators and engineers with coming up with the idea. “Our team works together really well. Everyone knows what’s going on here. We’re all committed to running this plant successfully, 110%.”

That makes it more than likely that the high school students touring the plant not only learn about science, they also see the value of employee education, open communication and institutional knowledge as well. As Esler puts it, “Before the tour, they’re pretty naive about wastewater. But when they see people from our area who have chosen a career in applied science and are making a difference, it helps give them a connection with the community and a sense of place.”