This article, by Cole Diepersloot, is part of a series highlighting members of the Office of Sustainability’s Experts Database. In a collaboration with instructor Hannah Monroe’s course, LSC 561: Writing Science for the Public, students interviewed campus sustainability experts and produced short feature stories.
According to the USDA, in 2022 more than 22 million acres of land in the U.S. were fertilized with some type of manure from farms. That’s enough to cover more than 60 percent of the state of Wisconsin. The use of manure as fertilizer, especially wastewater (mainly a mixture of manure and water), creates concerns for pollution. If not properly managed, wastewater can cause nutrient runoff that pollutes sources of fresh water and can also create gases that harm the atmosphere.
These concerns make wastewater research a priority since manure and wastewater production continue to increase alongside animal agriculture to meet the demands of a growing population. Responding to this need, innovators like Mohan Qin, an assistant professor for UW–Madison’s College of Engineering, are working to make wastewater more environmentally friendly. By recovering resources from wastewater, such as nutrients that can be used to grow crops, in more stable forms, she aims to reduce the negative environmental impacts of farming.
Qin’s group is developing technology to recover nitrogen from wastewater that can replace manure or commercial fertilizers used to grow crops. Recovered nitrogen is easier to transport and can be used more precisely than manure, as excess nutrients can be transported to other areas that would benefit. This makes it an appealing alternative to farmers compared to applying manure to fields directly.
Importantly, nitrogen recovered from wastewater is also more stable, which decreases the chances of pollution and protects sources of freshwater and the atmosphere. Recovering resources like nitrogen from wastewater has real potential to increase the sustainability of farming.
However, resource recovery from wastewater remains difficult with much of the research surrounding it still in its infancy. Instead of letting this deter her, Qin appreciates the challenge this brings to her research.
“I think I was interested in wastewater at the very beginning because of its complexity … no matter what kind of wastewater we are talking about,” she said.
Qin focuses on comparing ways to extract nitrogen from wastewater produced by farms. The process begins by allowing bacteria to convert nitrogen from the organic form found in wastewater to ammonia, the inorganic form of nitrogen that is more stable. Although this process is more established, capturing the ammonia efficiently is difficult, and Qin’s group is testing different methods of membrane distillation and electrochemical processes to capture ammonia.
Membrane distillation involves applying heat to the wastewater so that the ammonia evaporates and becomes a gas. Then a membrane, a selective material that only allows ammonia to pass through, contains the remaining wastewater so that the pure ammonia can be collected.
Electrochemical processes also use a membrane, similar to membrane distillation, but don’t require evaporation. In this case, an electrical charge is passed through the water that helps ammonia cross the membrane while the rest of the wastewater remains on the other side.
Although these methods of nitrogen recovery are promising, the complete process remains complicated. Qin expl
ained, “We need to fix B, C, D, E, F (…) before we achieve goal A.” For example, the makeup of wastewater can vary from farm to farm, depending on the type of animals, what they eat, and other factors. This means that one set of processes can recover nitrogen in one scenario but not work well in another.
This, along with other challenges that pop up during her research, is what keeps things interesting for Qin. Her group is working on perfecting processes that work across a wide range of wastewater so this technology can be used on a wide range of farms, and maybe even on other types of wastewater.
While her path has begun with nitrogen recovery, Qin ultimately strives to develop technology that can completely recover all resources from wastewater and put them to use, either in agriculture or other capacities. This means extracting all nutrients that could be used to fertilize crops, recovering clean water that can be used for animals or people, and capturing CO2 produced by microbes for energy or other uses.