Conference on treatment wetlands comes to Big Sky in August

By Marshall Swearingen MSU News Service

ENNIS – On a June day when snow lingered on the peaks of the Madison Range, Jack Wallis personified Montana State University’s Trout U moniker not with a fly rod in hand but with an 8-foot section of PVC pipe fitted with a wide vacuum nozzle.

As hefty rainbow trout lazed in the long, concrete-sided pools inside the Ennis National Fish Hatchery, Wallis steadily worked the apparatus through the water with the concentration of casting a dry fly, using the vacuum to suck up a sludge of fish food and excrement that had collected near a grate.

“I was pretty excited when I got to work on this project,” said Wallis, an angler who visits Montana’s alpine lakes when he’s not earning his master’s degree in environmental engineering at MSU. With this project, he explains, he gets to be around fish while working toward his goal of a career in wastewater treatment.

From the vacuum pipe, the sludge-filled water traveled through pumps, valves and tanks that directed the flow to the most important part of the system: a wetland constructed in order to treat the effluent. In the artificial wetland’s beds of sand and gravel, underlain by drainage pipe and an impermeable liner, the roots of sedges and rushes host microbes that feast on the fish sludge and purify the water.

“We’re using the same microbial processes as in wastewater treatment plants,” Wallis said. “It’s just in the form of a wetland instead of a mechanical system.”

Wallis is part of a team of researchers in MSU’s College of Engineering that has partnered with the U.S. Fish and Wildlife Service, which operates the Ennis hatchery, to study the use of what are called treatment wetlands, which are relatively rare in the U.S.

“This project is the first of its kind at a federal fish hatchery,” said Connie Keeler-Foster, who manages the Ennis facility. “A lot of our engineers are looking at this very closely. If it works, they could use it for other hatcheries as well.”

The impetus for the project came a few years ago, when stricter effluent requirements prompted USFWS to consider new treatment options for the Ennis hatchery, which produces about 20 million rainbow trout eggs annually for hatcheries nationwide.

Meanwhile, Otto Stein, professor of civil engineering at MSU, was ramping up his research on the use of treatment wetlands, which are widely used in Europe to treat sewage from subdivisions and small towns, he said.

“We’re on the cusp of a lot more of these systems starting to be used [in the U.S.],” Stein said. Compared to some other, more traditional wastewater systems, treatment wetlands “can achieve comparable, or even better, water quality for a fraction of the cost.”

Stein was looking for ways to test large prototypes, and found that treating the hatchery’s effluent would be similar to treating sewage. After weighing different options, USFWS decided to partner with MSU to try the low-cost method. 

During summer 2015, USFWS equipment operators, with guidance from Stein’s team, did the bulk of the construction, which involved excavating 3-foot-deep trenches roughly 10 feet wide by 100 feet long. The MSU team then helped lay down rubber membrane, which prevents the effluent from seeping into the ground, followed by drainage pipes and a thick layer of gravel and sand in which the sedges and rushes were then planted.

In September 2016 the hatchery began using the system to treat the sludge, which USFWS employees typically vacuum from the fish pools about once per week.

Wallis programmed the computer system that controls the valves and pumps. He also designed a filter system that will be used to remove phosphorus, a component of the effluent that the wetland doesn’t remove in significant quantities.

In June, the MSU team visited the site to install additional plants in the wetland’s 10 units, which are each about 100 square feet. The individual units allow the researchers to apply the effluent at different rates and monitor the effects on plant growth and water quality. The results could help the hatchery optimize the system, and could also improve the design of other treatment wetlands in the future.

“What appears to be a low-tech solution works because of a lot of sophisticated science,” said Chris Allen, an adjunct instructor in the Department of Civil Engineering who helped with the Ennis project while earning his Ph.D. from MSU.

Still, in terms of how the wetland plants interact with the microbes that break down the effluent, “we still don’t fully understand what’s happening in the subsurface,” Allen said. “That’s a rich field to explore.”

In August, scientists and engineers from around the world will visit the Ennis hatchery as part of the 7th International Symposium for Wetland Pollutant Dynamics and Control (WETPOL), a preeminent biennial conference about treatment wetlands. The conference, which will take place at Big Sky Resort on Aug. 21-25, is being hosted in the U.S. for the first time with help from MSU.