Selective recovery of formic acid from wastewater using an ion-capture electrochemical system integrated with a liquid-membrane chamber

Achieving Paris Agreement temperature goals requires carbon neutrality by the middle of the century. Carbon resource recovery from wastewater is recognized as an effective strategy to reach carbon neutrality. However, few technologies can selectively recover high-quality carbon resources from wastewater. Here, we propose a creative Ion-capture electrochemical system (ICES) simply constructed by integrating a Liquid-membrane chamber (LMC) inside that successfully recovers Formic acid (FA) from wastewater containing a high concentration of Cl−. In the charging process, negatively charged HCOO− that enters the LMC will immediately be converted to uncharged HCOOH by obtaining free protons (H+) from the acidic extraction solution, thereby realizing the selective separation of FA from coexisting ions. Under the optimal conditions (i.e., water productivity = 58.8 L/(m2 h), current density = 13.3 A/m2 and pHext = 1.62), an FA product with a high concentration (1586–1827 mg/L) and high purity (80.6%–84.1%) was obtained in semi-continuous operation (14.5 h) while sustaining low energy consumption (2.43 kWh/kg FA). In addition, the process can be applied more broadly to the recovery of various carboxylic acids, such as Acetic acid (AA) and Propionic acid (PA), by using alternative extraction solutions (for example, HCl, H2SO4 and HNO3). The results of this study suggest that an array of efficient and multifunctional processes can be developed through modification of traditional cell configurations for carbon resource recovery.