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Ten years from now, wastewater treatment plants will look and function very differently than they do today, according to Daniel Noguera, a professor of civil and environmental engineering at the University of Wisconsin-Madison.

For example, “recovered resources may not only include clean water and energy, but also a variety of chemicals, such as fertilizers and precursors of plastics and fibers,” Noguera continued.

Noguera and his team of researchers at UW-Madison believe this to be true thanks in large part to a complex family of bacteria that thrive in today’s wastewater treatment plants.

Not discovered until 30 years ago, anammox bacteria’s name reflects its function: it turns ammonium into nitrogen gas under anaerobic conditions. This is important since a conventional wastewater treatment plant converts ammonium, which is toxic to fish, into nitrogen gas and nitrate. Nitrogen gas is released into the atmosphere, while nitrate—an important plant nutrient—stays in the treated water. Regulations on the amount of nitrate that can be released vary by state, but excess nitrate contributes to algal blooms in natural bodies of water, depleting oxygen levels for aquatic organisms.

Not only can anammox bacteria convert a larger amount of ammonium to nitrogen gas, but they also have the potential to save plant operators a lot of money.

“Being able to remove ammonium anaerobically is pretty important because about 50 percent of a sewage plant’s operating cost is pumping oxygen into the water,” said Noguera. “Some of this oxygen is needed to remove ammonium with the conventional method.”

But the bacteria don’t save money and extract valuable resources by themselves—they have help, which is the topic of the paper published by Noguera and colleagues yesterday in the journal Nature Communications.

Much like the mutual symbiosis between clownfish and anemones, anammox bacteria partner with heterotrophs. The heterotrophs receive the organic carbon they need to grow from the anammox bacteria in the form of several specific molecules; and in return, the heterotrophs convert nitrogen into a form that anammox bacteria require for growth.

“We knew very little about the role of the bacteria that coexist in anammox granules,” Noguera said. “For the first time, our study identified detailed gene expression levels in these granules. This provides important clues on what the anammox bacteria and their partners might actually be doing, and how they interact.”

Of course, the bacteria don’t come without a set of challenges for wastewater treatment facilities. The bacteria grow slowly, taking about seven days to double in number. They also require closely monitored oxygen and temperature cycles, increasing operational complexity.

Still, Noguera believes the future role of wastewater treatment plants is bright. Some actually already produce more energy than they need to operate from the biogas that forms during the breakdown of organic material. And as research continues, potential is expected to grow.

“As part of this evolution, I believe anammox reactors will soon become conventional,” Noguera said.

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