Matthew Junjie Liu

Stanford

“Electrifying Chemical Transformations and Separations to Valorize Wastewater Nitrogen”

I study electrochemical reactive separation processes that enable simultaneous water treatment and resource recovery. I combine reactor engineering and process design to enable selective separations of ammonia from real wastewaters. An equally prominent thrust of my work is investigations of electrocatalysts that enable efficient conversion of wastewater nitrate to ammonia.

ABSTRACT

Sustainably managing the nitrogen cycle has been identified as a Grand Challenge by the U.S. National Academy of Engineering. Haber-Bosch ammonia () production has enabled large-scale food production; however, the Haber-Bosch process demands exorbitant energy inputs while directly yielding atmospheric carbon emissions, and the resulting perturbations to the global nitrogen cycle threaten water quality. Enabling a sustainable food-energy-water nexus requires feeding a growing population while minimizing environmental impacts. My research reimagines wastewaters as valuable feedstocks from which reactive nitrogen emissions (e.g., ammonium, ; nitrate, ) can be recycled to high-purity ammonia. Electrochemical driving forces are poised to precisely control the multistep process of ammonia recovery via renewable electricity. and are the most prevalent waterborne reactive nitrogen pollutants and therefore present tremendous opportunity for resource recovery. Whereas ammonium-rich wastewaters require selective separations for ammonia recovery, nitrate-rich wastewaters require selective conversion of to prior to separations. Thus, I study electrochemical reactive separation processes that co-locate electrocatalysis and separations to enable simultaneous water treatment and ammonia recovery. My work furthers environmental protection and sustains chemical manufacturing by developing negative nitrogen emission technologies while offsetting the Haber-Bosch process.
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