Industrial partnership seeks answer to microbial mystery
There is a mystery at the heart of all biological wastewater treatment systems. Theory provides a satisfying, useful and easy-to-teach explanation, but greatly oversimplifies the biological details. Now, however, sophisticated scientific techniques are available that can illuminate the true complexity and are helping to remove much of the mystery.
Developing a more complete understanding of wastewater treatment biology is important to USFilter's Envirex Products division in Waukesha. The company has been installing their OrbalTM biological wastewater treatment system for municipalities and industry since the 1960s. Compared to other systems, USFilter says the Orbal process removes more regulated nutrients while using as much as 30 percent less energy.
With support from USFilter and grants from the National Science Foundation, Assistant Professor of Civil and Environmental Engineering Dan Noguera is working to explain the Orbal system's efficiency. Envirex Director of Research and Development Peter Petit says his company is already benefiting from Noguera's work.
"There are skeptics out there," says Petit. "There are people who say, 'That is not how it is done in the textbooks so we don't believe you.' And we can say we have many operating plants that demonstrate that this can be done but often people won't let us take them that far. What Dan's research does is to help put a scientific foundation under what is currently sort of a black box. Instead of asking people to take this on faith and experience, this research is helping to explain the concept and has already helped us overcome skepticism in some cases."
Concentration of nutrients like nitrogen and phosphorus pose a number of environmental problems. Efficient, low-cost removal of these nutrients from wastewater gives industry and municipalities more options for discharging treated water to rivers, streams and lakes.
Nitrogen in municipal wastewater comes mostly in the form of ammonia. To remove it, explains Envirex engineer Chuck Applegate, a traditional activated sludge wastewater treatment facility employs separate tanks requiring separate groups of bacteria. Two different groups of bacteria are used to oxidize ammonia into nitrate. An additional step employs a different group of bacteria to reduce nitrate to nitrogen gas. The first step requires oxygen. The second requires the absence of oxygen.
"Instead of two separate tanks performing nitrification and denitrification sequentially, the Orbal system uses one tank," says Applegate. "By adding oxygen in that anoxic tank, the two things happen simultaneously."
Noguera is testing a hypothesis that attributes the system's success to bacteria that efficiently oxidize ammonia to nitrate at very low oxygen conditions.
"We have not identified the organisms, but we have developed molecular evidence by looking at the genes of the organisms present and comparing them with the genes of organisms in traditional treatment plants," Noguera says. "That gives us a hint that there is a different group of ammonia oxidizing bacteria in the Orbal plant. If we find this organism and demonstrate that it really works better at low oxygen concentrations, we will have very strong scientific evidence that explains why these plants are so efficient and why they work better than other plants."
Nitrogen in the environment is a growing concern. States are increasingly requiring its total removal from wastewater in addition to regulations requiring phosphorus removal. Noguera says phosphorus removal requires an anaerobic stage in which both nitrate and oxygen are absent. One must get rid of the nitrate to treat the phosphorus.
"That's an added incentive for this research," Noguera says. "The Orbal process is designed to remove nitrogen, but we have done experiments with full-scale plants and have found that the system also removes phosphorus."
So why is the phosphorus being removed? That is another mystery and the second part of Noguera's research. Is there yet another unidentified organism or is it that the organisms believed to do phosphorus removal also grow in aerated anoxic conditions? Noguera intends to find out.