To meet Department of Ecology regulations, the city of Pullman will soon finish installation of a $6 million system that treats wastewater with ultraviolet radiation.

Expected to be fully installed by September, the system will pass water through short-wavelength, UV radiation to kill or disrupt microorganisms at the city’s wastewater treatment plant before it is discharged into the south fork of the Palouse River.

The UV system will replace current city methods, which use chlorine and sulfur dioxide to disinfect wastewater and mitigate chemical byproducts before it is discharged into nearby waterways.

Not only will the new system eliminate the possibility of the city violating discharge requirements related to chlorine and byproducts of the chemical disinfection process, which has been a problem in recent years, it will also be safer for city employees who will be handling fewer chemicals on the job.

“With the UV system, there’s no chemicals. All the chemicals pretty much go away for that part of the process,” Pullman Director of Public Works Kevin Gardes said. “They basically emit light at a certain wavelength that’s germicidal to bacteria so, from an environmental standpoint, it’s a pretty low cost, pretty low impact.”

While the equipment was purchased in late 2017, Gardes said the project was delayed slightly so work could be timed with the summer months.

“We have to keep the existing treatment plant running while we do all this construction work and the work is taking place in an existing treatment basin,” Gardes said. “When the students are gone over the summer, we’re able to get by on just half of the basin so we can work in the other half, which is where this UV equipment is going.”

The UV system will also be capable of meeting both the city’s current discharge requirements for disinfection byproducts as well as Class A reclaimed water standards if the city were to elect to construct such a system in the future.

Gardes said if the city were to engage in water use practices with tighter restrictions — like those for cities that reuse wastewater — officials may consider supplementing the UV system with chlorine additives, but nowhere near the levels they were forced to use in previous years.

Gardes said with the exception of higher costs associated with running and maintaining the new system, there are few disadvantages to treating wastewater with ultraviolet light.

“You’ve got higher electricity costs but otherwise I don’t know that there’s any huge drawback to it,” Gardes said. “It’s going to be more expensive for us, so I suppose from a dollar standpoint it’s going to cost a little more but from an environmental standpoint, it’s better.”

Scott Jackson can be reached at (208) 883-4636, or by email to

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