The nitrate runoff issue, a source of carcinogens and a cause of suffocating algal blooms in U.S. rivers, may not be all gloom and doom. A recent research lead by the University of Illinois Urbana-Champaign presents a strategy for the integrated collection and conversion of nitrate-contaminated waters into valuable ammonia inside a single electrochemical cell.
The study, directed by chemical and biomolecular engineering professor Xiao Su, demonstrates a device capable of an eightfold concentration of nitrate, a 24-time enhancement of ammonium production rate and a greater than tenfold enhancement in energy efficiency compared with previous nitrate-to-ammonia electrocatalysis methods.
“By combining separation with reaction, we addressed previously established constraints of manufacturing ammonia straight from groundwater, where the quantities of nitrate are relatively low, and hence make the conversion step inefficient,” Su added.
“The purpose of our research was to utilise as little energy as possible to extract nitrate from agricultural runoff before it touches our rivers, and change it back to a fertiliser or sell it as a chemical feedstock,” Su said. “Our method may therefore have an influence on waste treatment, sustainable chemical manufacturing and progress decarbonization. We are attempting to introduce more circularity into the nitrogen cycle.”
The researchers created a novel, bifunctional electrode that can isolate and up-concentrate nitrate from a water stream, while converting to ammonia in a single unit using simply electrochemical control. “The bifunctional electrode combines a redox-polymer adsorbent, which absorbs the nitrate, with cobalt-based catalysts that promote the electrocatalytic conversion to ammonium,” Su added.
The system was tested in the lab using agricultural runoff collected from drain tiles surrounding the U. of I. research farmlands to assess the viability of the device for real-world situations, the researchers stated.
“This is a really efficient collection and conversion platform with a modest footprint,” Su added. “We don’t require separate electrochemical cells for the water purification and ammonium generation or adding additional chemicals or solvents. Instead, we imagine a module planted directly onto farmland and operated using the electricity produced from the electrocatalytic process plus a tiny solar panel.”
The team stated its next objective is to create even more selective materials utilised in the device to achieve better nitrate removal and expedite the conversion to ammonia—while developing bigger scale systems for realistic deployment in the field.
Kwiyong Kim is the primary author of the work, with assistance from Jaeyoung Hong and Jing Lian Ng, from the Su group. The experiment was carried out in partnership with Tuan Anh Pham, from the Lawrence Livermore National Laboratory, and Alexandra Zagalskaya and Vitaly Alexandrov, from the University of Nebraska.
Su also is linked with the Beckman Institute for Advanced Science and Technology and also is a professor of civil and environmental engineering at Illinois.
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