Efficient bicarbonate removal and recovery of ammonium bicarbonate as CO2 utilization using flow-electrode capacitive deionization

The use of wastewater for CO2 mineralization is a promising strategy that not only addresses environmental issues (i.e., preventing greenhouse gas emissions and algal blooms by CO2 removal), but also produces economic benefits (i.e., recovery of carbonate-based minerals). In this study, we propose an innovative flow-electrode capacitive deionization (FCDI) system for efficient bicarbonate ion (HCO3-) removal and ammonium bicarbonate (NH4HCO3) enrichment from synthetic swine wastewater, which commonly contains excessive ammonium ions (NH4+) and HCO3-. The effects of different operational parameters for HCO3- removal and enrichment were investigated. At optimal operating conditions, we achieved approximately 1.61 M of NH4HCO3 concentrated solution with 97.2% of purity in 30 h with a C removal rate of 1.01 kg C m(-2) d(-1) and energy consumption of 2.87 kWh kg(-1)C. This is a removal rate of approximately 2-5 times greater than other electrochemical systems and 25% less energy consumption. In addition, the feasibility of the NH4HCO3 enrichment via the FCDI system was also verified by X-ray diffraction (XRD) analysis and Raman spectroscopy. This work provides an efficient strategy for NH4HCO3 enrichment from swine wastewater and a great potential to expand the scope of CO2 utilization.