CAREER: Molecular Electrocatalysts and Reactive Separations for Wastewater Nitrogen Refining

The utilization of nitrogen (N) fertilizers has been critical to maximizing crop yields in agriculture and farming to feed a growing world population. Unfortunately, the release of excess N (nitrate) from agricultural runoffs and wastewater treatment plants has also led to widespread groundwater pollution and nutrient enrichment in surface water systems, a process commonly referred to as eutrophication.

In nitrogen-limited surface water systems including lakes, rivers, and estuaries, eutrophication has been shown to cause a decrease in water quality, oxygen depletion, a loss of aquatic biota, and the occurrence of harmful algal blooms. The overarching goal of this CAREER project is to explore the utilization of electrochemical refining to recover nitrate from wastewater and convert it into valuable products such as ammonia which is a critical component of N fertilizers.

To advance this goal, the Principal Investigator proposes to combine and integrate chemical separations (membranes), electrocatalysis (nitrate reduction reactions), process modeling, technoeconomic analysis (TEA), and life cycle assessment (LCA) to design, develop, and optimize reaction and separation systems that can capture, concentrate, and convert nitrate from wastewater sources to high purity ammonia. The successful completion of this project will benefit society through the generation of new fundamental knowledge and technology to advance the mitigation of nitrate pollution and enable a circular nitrogen economy.

Additional benefits to society will be achieved through education and training including the mentoring of one graduate student at Stanford University.

The management of the global nitrogen cycle has been identified as one of the 14 Grand Challenges for Engineering by the US National Academy of Engineering. Electrochemical refining has emerged as a promising technology to advance a circular nitrogen economy as it can be utilized to tune the oxidation states, transport, and conversion of nitrogen pollutants from wastewater to valuable products at potentially lower cost with reduced chemical inputs and emissions than existing commercial technologies.

This CAREER project will investigate the electrochemical reduction of nitrate from wastewater to produce ammonia, a critical component of nitrogen fertilizers. To advance this goal, the Principal Investigator (PI) proposes to design, synthesize, evaluate, and optimize a new family of homogenous molecular catalysts [M(DIM) catalysts, where M is a transition metal (Co, Fe, Mn, Cu, Ni) at the center of a dimethyl ligand (DIM)] that could enable the rapid, selective, inexpensive, and energy-efficient electrochemical nitrate reduction to high-purity ammonia.

The specific objectives of the research are to 1) design and synthesize molecular M(DIM) catalysts and elucidate their mechanisms of nitrate reduction in various wastewater matrices; 2) design and engineer extraction systems to separate the catalysts and their reaction products (ammonia) from treated wastewater; and 3) design, develop, and optimize electrically driven reactive and separation systems that could be integrated into wastewater treatment plants to recover and convert nitrate to high-purity ammonia. The successful completion of this project has the potential for transformative impact through the generation of new fundamental knowledge to advance the design and development of more efficient and cost-effective wastewater treatment processes and systems to recover and convert nitrate to valuable products.

To implement the educational and outreach activities of this CAREER project, the PI proposes to leverage existing programs and resources at Stanford University to design and launch an annual Bay Area Electrochemistry (BAE) Bootcamp to train early-stage graduate students on electrochemical methods and circular water treatment applications. In addition, the PI proposes to 1) develop and implement an REU program augmented with seminars on societal equity to recruit and retain undergraduate students from underrepresented groups and 2) design and organize water-related science fair projects to engage and mentor high school students from underrepresented groups.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.