(68c) Remediating and Valorizing Nitrogen-Polluted Wastewaters Via Electrodialysis and Nitrate Reduction

Fertilizer runoff and inadequate wastewater removal cause waterborne emissions of reactive nitrogen (e.g., NH₄⁺, NO₃^–) that induce harmful algal blooms. Meanwhile, both water purification and ammonia synthesis are conducted separately in centralized facilities with severe limitations. We propose a novel electrochemical process, Electrodialysis and Nitrate Reduction (EDNR) to efficiently couple water purification and ammonia production from nitrogen-polluted wastewaters.

The EDNR reactor consists of three chambers and operates in two stages (Fig. 1a), with the influent entering the middle chamber and products recovered from the left and right chambers. In stage 1, influent NO₃^– and NH₄⁺ are separated via electrodialysis (ED) and ammonia is recovered in the right chamber. In stage 2, ammonia is synthesized from the electrochemical nitrate reduction (NR) in the left chamber.

We have demonstrated proof-of-concept EDNR reactors using titanium foil (left chamber, NR electrode), Ti/IrO₂-Ta₂O₅ mesh (left and middle chambers, ED electrode), and Pt foil (right chamber, ED electrode). With recirculating batches of simulated wastewater (100 ppm NO₃^– + 500 ppm NH₄⁺) for three cycles (9 hours, Fig. 1b), 75% influent NH₄⁺ was recovered into the right chamber and 25% influent NO₃^– was converted to NH₄⁺ in the left chamber (Fig. 1c and 1d). Furthermore, the performance of EDNR can be readily adjusted to various influent conditions by rationally designing the electrochemical environments (e.g., electrode material, initial electrolyte composition) in each chamber and controlling the operational parameters (e.g., current density, electrode potential, influent flow rate, stage period). Our preliminary results have shown that the addition of Na⁺ promotes NR performance in influent with low NO₃^– concentrations. Such flexibility allows us to have controllable and stable water remediation and ammonia production from unstable and uncontrollable wastewaters.

As a validated and highly tunable platform, EDNR shows great potential in realizing sustainable and distributed water remediation and ammonia production.