Co-capture and resource recovery of ammonia and carbon dioxide in microbial electrolysis system with an assisted carbon capacitor chamber

Human activities lead to the excessive input of carbon and nitrogen elements into the water and atmosphere. The recovery and recycling of carbon and nitrogen have been gaining increasing attention. The microbial electrolysis cell (MEC) is anticipated to simultaneously recover nitrogen from wastewater and capture carbon from the atmosphere. In this study, a process for carbon and nitrogen co-capture, utilization, and storage centered on MEC (MEC-CNCUS) was proposed to reduce energy consumption and achieve carbon and nitrogen resource recovery and recycling. A three-chamber MEC system was developed, where ammonia nitrogen from sewage migrated across the membrane to the cathode chamber, and bicarbonate from the absorption chamber was simultaneously captured at the cathode driven by alkalinity gradients. The NH₃ and CO₂ released from the carbon-nitrogen co-absorption solution upon heating were fixed by CaCl₂ slag to produce nitrogen fertilizer and nanometer CaCO₃ products. With the optimal replacement frequency (12 h⁻¹) and concentration (70 mmol L⁻¹) of the CO₂ adsorption solution, 55.1 ± 0.25% of ammonia nitrogen in the anode migrated to the cathode, and the inorganic carbon content of the catholyte increased by 31.54%. Following heating, the ammonia nitrogen was almost entirely transferred to liquid fertilizer, the CO₂ recovery rate reached 54.6 ± 0.41%, and cubic nano-calcium carbonate product with good dispersion was obtained. The MEC-CNCUS system offers a potential technical approach for simultaneously achieving wastewater energy utilization, ammonia recovery, and carbon sequestration.