Using a Wetland to Clean Our Water

By Carol Flaherty

09/22/00 BOZEMAN, Mont. - Here's the test:    What do you think of if someone says "bulrushes?"

            The odds are you thought of Moses. You might even have thought that there was a space between the syllables and responded "bull fights." But ask Otto Stein or Paul Hook the same question, and they're much more likely to say something like "water treatment."

            Stein and Hook are finding out just how much nature can do to help us clean up after ourselves. Stein is a civil engineer at Montana State University. Hook is a biologist in the MSU Land Resources and Environmental Sciences Department. For the past three years, the two have been studying how manmade wetlands can be used to treat organic waste – whether it is agricultural or human.

Water treatment test at MSU

            With several moderate-sized grants from organizations such as the Montana Water Center, the Bureau of Reclamation, the Environmental Protection Agency, US Geological Survey, the USDA and the Montana Agricultural Experiment Station, they constructed miniature wetlands in tanks at MSU's Plant Growth Center. The microbes, cattails, sedges and bulrushes in the tanks clean the wastewater they pump through the system.

            If you walk into the lab expecting an odor like sewage , you'll be disappointed. The experimental systems remove the smell as well as most of the pollutants in the wastewater that is rich in organic matter. The eight 2.5 by 5-foot lab's wastewater treatment wetlands treat about 800 gallons a week, cleaning it of about 90-95 percent of it's dissolved organic carbon, and up to 80-95 percent of nitrogen when in smallest column tests.

            Big cells remove more carbon, small cells remove more nitrogen, even though both receive the same amount of water, says Stein. "I think when we test it pulsing the water into the systems will improve the nitrogen removal, but that is for a later experiment," he adds.

            Scientists already know that wetlands clean water, but Stein wants to understand the system enough to predict where and how much a wetland can help treat our waste. Predictability of wastewater treatment could increase wetlands use for that purpose, especially in colder climates where their adoption for secondary water treatment has been limited.

            "Traditional waste water treatment dogma says there is a very strong relationship between temperature and the length of time needed to treat waste," says Stein. That kind of thinking has dampened the enthusiasm for research into the benefits of wetlands in colder areas, even though such treatment can be very economical compared to other options.

            But Stein says the key to thinking about wetlands is to separate the idea of air temperature from water temperature.

            "The key is water temperature, not air temperature," says Stein. "The morning air could be below zero, but the water may still be unfrozen underground." Their work has shown water cleansing underway in wetland systems when the water temperature is just 36 degrees Fahrenheit.

            Hook adds that a water temperature 36 degrees F can be maintained in Montana and other northern climates with plant debris and snow cover to insulate the ground.

            The current dogma also says that what plants you have in a wetland is not very important because the treatment done by bacteria in the water.

            But Hook has found that -- contrary to most previous wetlands research-- the type of plant matters a lot, especially in winter. Stein thinks the reason the role of plants has been thought minimal was because much of the earlier research was done in warmer climates.

            "At warm temperatures, gravel, plants and water cleanse wastewater only slightly better than the same system without plants. However, water treatment at cold temperatures improves dramatically when plants are a part of the system, says Stein.

            The top "pollution-eating" plants tested so far are sedges and bulrush. Either does a considerably better job than cattails.

            Stein and Hook think this is proof that there is a lot more to be learned about the cleansing abilities of other wetland plants, since they simply chose sedge and bulrush from among many possibilities because the two are widely available native plants.

            Understanding wetland plants' contribution to wastewater treatment has been complicated by the fact that early studies were most often done with cattails in warmer climates. In warm climates, the microbes seem to do most of the work, making the plants look inconsequential. In addition, cattails just don't "work very hard" in winter. However, Stein and Hook's studies show that sedge and bulrush remove carbon and nitrogen relatively completely year around, even though there is a spring/fall variation even at the same temperature.

            Organic carbon is the primary pollutant the two are trying to control with wetlands. Controlling carbon is important because when it enters a stream, it depletes oxygen. If there is too much carbon, the free oxygen is eliminated from the system, harming fish and other life.

            You don't hear much about organic carbon pollution, says Stein, because municipal water-treatment systems can handle it rather well. But it is hard to get money to increase water treatment capacities as a town grows. Stein and Hook hope wetlands systems can be used to extend the life of those facilities or minimize the size and cost of new facilities, helping towns, reservations, even individuals treat wastewater economically.

            In a private setting, a wetland may even be viewed as a special garden or added amenity.

            Roger Perkins is a homeowner near Laurel and owner of Aquoneering, a water engineering firm. A few years ago, he put in a small wetlands just below the septic drain field at his home.

            "I bought 10 or 12 old bathtubs from a hotel renovation and put them in the ground," says Perkins. He filled them with three-quarter inch gravel and planted cattails and bulrush.

            "I wanted to see if I could reduce the nitrogen coming out of the septic system," says Perkins. He tested the effluent at the exit of the septic field, and again at the drainage from the bathtubs, but was disappointed with the improvement. He adds that he plans to improve the system, perhaps this fall. He also plans to try adding plants that will give a more decorative effect.

            "We're up on a hillside, and the cattails and rushes looked out of place in the yard. For a home setting, it would be nice to have some color," concluded Perkins.

            In 1997, Ronan installed a wetland of cattails to deal with an odor problem, says Jim Morgan, assistant public works director and wastewater operator there.

Wetland water treatment at Ronan
            "We finished it in 1998. . . . We haven't had any odor since then," said Morgan.

            Ronan is using what is called a "two-celled" system, each is 3.5 acres on the southwest side of town. Morgan said the town had been over-permit levels a few times on total dissolved solids and biochemical oxygen demand, a standard measure for the amount of organic matter in the water.

See also story on Students Supported by Wetland Research.

Send questions or comments to Hook, Stein and Carol Flaherty, MSU Communications Services, Bozeman, MT 59717: carolf@montana.edu.

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