(667c) Biomimetic, Molecularly-Designed Adsorbents for Selective Nitrogen Separations in Wastewater

The presence of nitrogen compounds, such as ammonium, in wastewater is concerning due to their contribution to eutrophication, which has a wide range of negative environmental effects. Removal of ammonium in wastewater streams is typically conducted through microbial nitrification-denitrification pathways that convert ammonium into dinitrogen gas. Unfortunately, this reverses the Haber-Bosch process, which consumes roughly 1% of global energy in order to convert dinitrogen gas into ammonia. A more sustainable and economically advantageous approach for wastewater treatment plants would be to implement technologies that efficiently remove ammonium from wastewater directly, then use it for value-added products, such as ammonium sulfate fertilizer. Ion exchange is a well-established technology for removing ionic impurities from water, but the resulting eluent stream currently requires additional cost-ineffective steps to further separate ions before value-added products can be made.

Therefore, we have fabricated an acrylamide-based, ammonium-selective adsorbent material, inspired by the KS-AMT5 ammonium transporter protein found in ammonium-oxidizing bacteria, for use in wastewater ion-exchange processes. Through the combined effect of multiple functional groups in close proximity, this material selectively binds to ions (like ammonium) that can engage in hydrogen bonding in addition to ionic attraction and cation-pi interaction. Ubiquitous monoatomic wastewater cations like sodium and potassium can only engage in the latter two. Batch and continuous adsorption tests reveal that our adsorbent exhibits higher ammonium adsorption capacity compared to commercial adsorbents. Ion competition experiments exhibit negligible sodium, potassium, and lithium adsorption compared to ammonium (high nitrogen selectivity). Additionally, the adsorbent is resistant to chemical degradation by the regenerant, 0.1 M sulfuric acid, which both removes ammonium and forms ammonium sulfate concurrently. By using this material, wastewater treatment plants will be able to directly remove ammonium and close the industrial nitrogen loop while preserving economic viability.