New wastewater treatment plant is good news for Missouri River

WILLISTON, N.D. - The first phase of a new Williston wastewater treatment plant is complete, greatly reducing the impact the growing city is having on the Missouri River. New equipment at Williston's plant is allowing the city to significantly cu...

Treated wastewater from Williston, N.D., discharges into the backwaters of the Missouri River on Friday, Dec. 4, 2015. New equipment at the plant allows the city to treat the wastewater to a higher level. Amy Dalrymple/Forum News Service



WILLISTON, N.D. – The first phase of a new Williston wastewater treatment plant is complete, greatly reducing the impact the growing city is having on the Missouri River.

New equipment at Williston’s plant is allowing the city to significantly cut back on how much wastewater is discharged into a marsh where several fish kills were reported earlier this year.

In addition, new technology the city has implemented is reducing the ammonia concentration in the wastewater to much lower levels than the city’s maxed-out lagoon system could accomplish.


Williston’s wastewater treatment plant receives about 2.3 million gallons per day, and previously all of that went through a 1970s-era lagoon system designed for a population of 10,000 to 15,000. The city’s service population is now more than double that size, in addition to industrial and business growth.

Because the lagoons were always full, Williston had to discharge about 3.85 million gallons of wastewater each weekday into a marsh that leads to the backwaters of the Missouri River.

“We were way above capacity,” said Gina Mottl, wastewater treatment superintendent.

With part of Williston’s new treatment plant complete, the city now sends about 300,000 gallons of wastewater per day to the lagoons. The lower amount will allow the city to discharge twice a year – once in the spring and once in the fall – rather than nearly every day.

“The impact to the marsh will be greatly reduced by the new wastewater treatment plant,” said Karl Rockeman, director of water quality for the North Dakota Department of Health.

When the $105 million plant is fully complete, expected in 2017, the city will phase out the lagoon system and discontinue discharging into the marsh.

Most of Williston’s wastewater now goes through new equipment called an oxidation ditch and a clarifier, a system that is reducing ammonia concentrations in the water to a fraction of what the plant could do previously.

“We’re well under where we need to be,” Mottl said. “A lagoon could never treat for ammonia the way this system can, and we can do it in about 36 hours.”


The health department issued Williston a notice of apparent noncompliance after hundreds of game fish, including northern pike and walleye, were reported dead in May 2014 in the backwaters of the Missouri River. Health officials attributed the fish kill to a lack of ammonia treatment in the city’s wastewater, which discharges into the river.

Today, however, Williston’s wastewater is far below the thresholds that would be harmful to the environment, Rockeman said.

“They’re putting out very good quality wastewater effluent from the plant,” Rockeman said.

Williston Public Utilities Director David Tuan said fish have recently been seen swimming toward the city’s wastewater discharge.

The new plant will serve a population of 60,000, and is designed so that it could be expanded in the future. In addition to serving the city of Williston, the plant will able to accommodate wastewater from the region and future industrial growth, Tuan said.

Williston spent an extra $1 million to fast-track construction and get phase one of the plant complete this year, a timeline the health department required for the city to be in compliance with its permit.

The final phase of construction involves the portion of the plant that will treat solid waste and turn it into a recyclable product the city plans to use for landfill cover.


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