The intensive use of fertilizers in EU regions is degrading sensitive water bodies. When these nutrients make their way into rivers, they considerably disturb aquatic ecosystems. Recycling the reactive nitrogen could reduce the energy needed to both produce fertilizers and dispose of nutrients, cutting greenhouse gas emissions on both ends of their production chain.
Electrochemical systems (ES) can be the new solution for this nitrogen issue, as they are capable to both remove and recover nitrogen. Earlier results using ES to treat urine showed an effluent with a lowered TAN (total ammonia nitrogen) concentration and a product with potential use as a fertilizer (ammonium sulphate).
Figure 1 illustrates a hydrogen gas recycling electrochemical system (HRES) including 4 compartments (anode, feed, concentrate and catholyte) for ammonia recovery. At the anode occurs the oxidation of H2 instead of water oxidation. The formed electrons move through an external circuit towards the cathode, where the reduction of water occurs.
The current supplied to the system drives the hydroxides formed at the cathode, across the AEM to the concentrate. Likewise, ammonium ions (NH4+) protonated in the feed, move through the CEM to the concentrate. As a result, ammonium is deprotonated to ammonia (NH4+ +OH- --> NH3). The formed NH3 can be recovered using a gas permeable hydrophobic membrane, such as transmembrane chemisorption (TMCS).
This project aims to improve and scale-up an electrochemical system for TAN recovery using different real wastewater streams (source separated urine, digester effluent, etc.) in a multiple stacked cell system. The process will be optimized to a simple and compact system, capable to treat a significant volume of influent and to achieve high TAN recovery at low energy input.