Two city of Boise public works employees are in Germany this week, inspecting new equipment that will sanitize more than 20 million gallons of city wastewater each day on its way to the Boise River. The ultraviolet light sanitization devices will replace aging units at the West Boise Water Treatment facility, one of two renewal sites where everything Boise, Garden City and Eagle residents send down sewer pipes ends up.
“Between Lander Street and West Boise, we're treating about 30 million gallons of wastewater per day,” explained Ben Nydegger, the city of Boise’s Water Renewal System Sr Manager. Between the two sites, the average daily flow is about 80 to 85% of total system capacity.
Solids bigger than about a pea are filtered out (a lot becomes compost), dissolved solids settle out in circular clarification pools about the size of a tennis court, microorganisms eat up what’s biodegradable in aeration basins about the size of a hockey rink, and then it’s back into another clarification pool. But the clarified water has one last step to be safe enough for its final destination: the Boise River.
“Welcome to UV,” Industrial Controls Lead at West Boise Clint Smith says, leading me into a large room reverberating with the loud hum of equipment and rushing water. Smith is among the group leading me on a tour of the 90-acre treatment facility, and cautions me as he lifts the lid on one of the banks of UV light.
“UV light is bright enough that you can get essentially a flash burn, like from welding,” he said.
The ultraviolet lamps are long and tubular, similar to fluorescent bulbs but larger and brighter, inside a clear protective sleeve.
“The UV rays sterilize any pathogens that will go to the river. The bulbs burn at a rate that is a mathematical equation of flow and TSS [total suspended solids] that essentially disinfects and sterilizes those pathogens as they pass through,” Smith explains.
Dozens of lamps are submerged in channels of clarified wastewater about six feet wide by six feet deep, glowing neon green. There are three UV devices; one in each channel.
“Each channel will accept the flow of the plant every day, and so we'll have double redundancy,” Smith said. That’s important for periods of high wastewater flows - like the melt-off from "snowmaggedon" in 2017, or when one channel needs to be cleaned, maintained or fixed.
“For a full rebuild, [it’s] every 12,000 hours. And that full rebuild includes bulbs, wipers and cleaning of the sleeve.
Two of the units are about 25 years old, the third is about 13 years old. All three are near the end of their designed life. That means, even with regular maintenance, there’s increased risk of failure. That’s why Smith is in Germany; to inspect the replacement units and training to use the upgraded equipment.
“I'm going to go in and I'm going to ask them to make it fail, because I want to know what it's going to do, what I have to do to get it back up and running,” he said.
Knowing what to do when things don’t go right can be the difference between days or hours of down time. Even though there are redundancies everywhere, unexpected down time is never comfortable, said Nydegger.
"We like to kind of joke that there's no such thing as a ‘no-flush Friday.’ We can't tell our community that they can't discharge to us for a day.”
The Boise City Council approved the $1.4 million dollar UV replacement project for West Boise in 2024, for up to $1.8 million. The single-bidder contract was signed in January last year. Those require special permission and special circumstances for approval. How the UV treatment building is constructed, with its three wastewater sterilization channels, was the determining factor.
"Our channels are about six feet deep,” explained Boise Water Renewal Program Manager Matt Plaisted. “Some of the manufacturer's equipment is eight feet deep, so we would have had to dig down a couple feet. Those are pretty extensive modifications to make.”
And expensive. Not having to modify the channels will save ratepayers a lot of money, he said. Germany-based Wedeco was the only manufacturer that fit the bill.
The new equipment will also save time and be safer for staff to maintain. Currently, cranes built in to the building are required to lift the units out of the channels. That process can take about one- third of the two-to-three hour maintenance process that happens every 500 days.
The new units can lift the UV light assemblies out of the water on their own.
“It really is going to speed up and improve the safety for what we're doing.”
Visiting an equipment manufacturer ahead of a major order is fairly common. The costs of the trip, up to $10,000 dollars for two people, is included in the contract. What’s not included: potential import tariffs.
President Donald Trump announced in July an import-export deal with the European Union, establishing broad 15% tariffs on goods imported from EU countries, including Germany. The deal reflected a lower tariff rate than what the President initially announced, in exchange for trade concessions from Europe. There are few exceptions, but different economic sectors can have different tariff rates.
Wedeco is a subsidiary of an American conglomerate, Xylem. It recently notified Boise of a nearly $94,000 increase in the contract; a contingency line for potential tariffs. That’s a 6.5% increase in the overall cost of the contract, but it’s not clear how Xylem reached that number; a company spokesman wasn’t able to answer that question by publication deadline.
The first replacement UV unit is expected to arrive in Boise this spring. Installation of all three is expected by late 2027.
“Right now we're anticipating it's going to be about six months per channel,” Plaisted said. “And we're still a few months out from construction beginning.”
This isn’t the only project at Boise’s water treatment plants. West Boise is getting a new aeration pool in 2028, that’s where the microorganisms clean the water. Existing aeration pools are being upgraded, and construction at the Lander Street treatment facility is on-going, with multiple upgrades planned through 2032.
Once completed, all the upgrades will add about 4.5 million gallons a day of capacity at West Boise, and the city’s renewal system will be capable of handling up to about 43 million gallons of wastewater a day.
