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Long collaboration with sewer district helps city, university

August 19, 2010 By David Tenenbaum

The passage of the Clean Water Act in 1972 ushered in a revolution in sewage treatment. Faced with tightening restrictions on the water and solids it must release after treatment, the Madison Metropolitan Sewerage District (MMSD) turned to experts at the University of Wisconsin–Madison for advice.

The goal of wastewater treatment is to remove dangerous organisms and chemicals from sewage, but many different chemical and biological processes can combine to do that job. In a collaboration that continues to this day, university engineers and scientists have helped the district meet ever-tighter standards on the release of nitrogen, phosphorus and ammonia, suggesting and testing effective processes that minimize the need for expensive new equipment.

UW-Madison researchers showed that ultraviolet light could replace environmentally damaging chlorine for killing bacteria before effluent is released into the Yahara River, accelerating the adoption of ultraviolet disinfection by many other sewage districts.

UW-Madison agronomists and soil scientists also helped perfect safe, beneficial techniques for disposing of the solid material remaining after processing; the district now sells a compost-like material called Metrogro to area farmers. With careful monitoring, this “biosolid” is injected into the soil, where it helps restore structure and fertility while reducing pollution of surface and groundwater.

Phosphorus has been a focus of concern since the Clean Water Act, says Daniel Noguera, a professor of civil and environmental engineering at UW–Madison who has collaborated with the district for a decade.

Because a phosphorus-bearing mineral called struvite is plugging equipment at the sewage plant, the district is considering whether to remove phosphorus before or after processing. “Both techniques sound great for preventing precipitation, but will they really work?” Noguera asks. In any case, he says, phosphorus is too valuable a fertilizer to be routed down the Mississippi River into the Gulf of Mexico, where it feeds algae in the notorious “dead zone.”

University researchers are approaching the phosphorus problem from two directions. First, graduate student Cheng Ji is investigating in the lab how much struvite will precipitate, using samples taken from the sewage plant, to simulate what will happen depending on which process is adopted at the plant. Second, students and Noguera have built what he calls “a very complex Excel model of the plant, looking at what will happen at the plant and how phosphorus will be redistributed once the new system is implemented.”

The long collaboration has saved money and provided a scientific basis for crucial design decisions, says Steven Reusser, MMSD’s operations engineer. “Some of the work showed that we can simultaneously remove organic material and ammonia, which saved a tremendous amount of tank construction.”

Another project discovered a more effective method for injecting oxygen into the heart of the wastewater treatment process, where bacteria break down complex molecules. “These bacteria use a huge amount of oxygen,” says Reusser, “and the newer diffusers are much more efficient because they make very fine bubbles. The blowers that supply air to these diffusers cost $30,000 to $40,000 a month for electricity, but the energy would cost at least twice as much if we were still using the older technology.”

The close collaboration with MMSD offers unique benefits to students, says Noguera. “It’s such a great interaction from an educational perspective. I have undergraduate students who are doing real research. Students who interview at a company need to have practical experience, and so the word is out: ‘Go talk to Noguera, he’ll put you to work.’ These guys are not playing in the lab; they get real experience working with real equipment and real people.”

Former students have found work at sanitary districts and engineering firms around the country, says Noguera, who also works on biological aspects of drinking water and energy production.

Is it difficult to attract students to work with something that most people want to flush and forget? “I sometimes wonder if students will say, ‘That’s terrible, I won’t work at the sewage plant,’ but that’s not occurred. They always find something interesting about working to release clean, safe water back into the environment.”

The mutual assistance arrangement perfectly reflects the Wisconsin idea, says Noguera, who in January was named a Wisconsin distinguished professor in recognition of the contributions his research has made to the state’s economy. “The district is an extremely progressive group of people; they are looking 10, 20 years ahead to think about what will be needed. This partnership reflects the Wisconsin Idea and is efficient from the point of view of helping the Wisconsin economy.”

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