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OREGON INSIDER December 15, 1995
<br /> * CONSTRUCTED WETLANDS & WASTE WATER
<br /> by Carol Savonen, Oregon State University
<br /> For the past four years, Jim Moore (professor of bioresource engineering, Oregon State University)
<br /> and his graduate students have studied constructed wetlands as a way of helping clean up waste water at
<br /> ,p,.
<br /> the Pope and Talbot pulp plant in Halsey, Oregon.
<br /> Pe P P P Y� g
<br /> Constructed or manmade wetlands are being successfully used for treatment of waste water from
<br /> �4 a paper or pulp mills, dairy farms, vegetable processing plants and meat packing plants and for managing
<br /> ' storm water runoff. These wetlands help remove significant amounts of nutrients, suspended solids and
<br /> soluble organic materials from the waste water
<br /> Constructed wetlands, however, are less predictable than traditional mechanized water treatment
<br /> systems such as sewage treatment plants. Moore and his graduate students are trying to better understand
<br /> the physical, chemical and biological processes of constructed wetlands so engineers can more effectively
<br /> , use them as a way of cleaning up waste water.
<br /> In constructed wetlands, the solids are removed by settling, then the liquids are treated biologically
<br /> • in shallow ponds with emergent aquatic plants such as cattails or bulrush. The plants provide surface area
<br /> for beneficial bacteria to live on and digest organic matter in waste water. They also pump oxygen into
<br /> :qx the system, which helps aerobic digestion to occur. Constructed wetlands are often cheaper and require
<br /> f - less labor to maintain than other means of treatment, such as gravel trickling filter methods.
<br /> ''t But waste water treatment in cattail and bulrush -laden ponds pose challenges for waste water
<br /> ;or engineers, who are used to working with the more predictable tanks, sprinklers and pipes, according to
<br /> < Moore. "Waste water engineers base their treatment on `ideal flow conditions,' " said Moore. "In a
<br /> ' w ,r constructed wetland, the conditions are far from ideal. Aquatic plants block and disperse flow. Some
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<br /> � • - ,� waste water flows through quickly. Other stays in the system a long time. These natural biological
<br /> systems are much more unpredictable."
<br /> Moore and his researchers compared the hydraulic characteristics of effluent and treatment effi-
<br /> ,; " ciency in constructed wetlands with cattail versus bulrush, pure gravel and open pond at Pope and Talbot
<br /> by measuring how fast dye moved through identically shaped ponds. They found that treatment with
<br /> ` : . , ° vegetation- filled constructed wetlands was only 75 percent as efficient as the models predicted.
<br /> ''t °' "We found that flow through created wetland ponds is not like the ideal model," said Moore.
<br /> "Some of the water spends 50 hours in the pond before it exits to the river. Some spends 150 hours.
<br /> ...This discrepancy is important to know. It will help engineers who use constructed wetlands for waste
<br /> water treatment understand why their treatments aren't as efficient as expected, and they can adjust their
<br /> #• • treatment process."
<br /> Moore also designed studies to compare how effective cattails and bulrush plants were at treat
<br /> 13ip effluent. He investigated differences in the decomposition of cattail and bulrush plants from the Pope and
<br /> Talbot effluent ponds and determined that bulrush provided better treatment for breaking down soluble
<br /> organic material in the water, while cattails were better at removin g solids. "Bulrush is slower to
<br /> ", , ," breakdown than cattails when it dies and falls in the water," he said. "Therefore, it provides substrate for
<br /> microbes that feed on soluble organic materials in the effluent. Cattails, with more plant surface area,
<br /> r E „ 'fft - break down faster, but provide better removal of solids."
<br /> "So waste water operators can choose what plants to put in their constructed wetlands depending on
<br /> ° the characteristics of their effluent," continued Moore. "For example, if they have more soluble organics
<br /> in the water, bulrush would be better to plant. If they have more solids, they might want to use cattails.
<br /> Information like this may some day allow scientists to have a catalog, where they could look up what
<br /> plants to include in their constructed wetlands based on the type of effluent they are treating."
<br /> The constructed wetland ponds at Pope and Talbot were shut down last year due to a wood chip
<br /> Dairies." shortage and a decision not to expand the plant. Moore and his students continue to assess optimal usage
<br /> of wetlands at ponds being constructed behind OSU's Campus Dairy, however. Some ponds will be used
<br /> to test whether constructed wetlands, rather than expensive tanks or filters, are a better means to clean up
<br /> the relatively clean waste water from dairy milking parlors. Other ponds will be studied for their
<br /> efficiency in the more problematic treatment of manure flushwater from Karns. If successful, these
<br /> methods hold much promise for greatly reducing the cost of required Dairy waste water treatment.
<br /> The specifics of the Polp and Talbot findings are available from Professor Moore at the number
<br /> below, including papers delivered on the subject.
<br /> • F'oR ADDITIONAL INFORMATION, CONTACT: Carol SaVOnCn, OSU, (541) 737 -3380; Jim Moore, OSU,
<br /> (541) 737-6299
<br /> Copyright() 1995 Envirotech Publications; Reproduction without permission strictly prohibited. 7
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