Sustainable desalination using a microbial capacitive desalination cell

Abstract

Microbial desalination cells (MDCs) use the electrical current generated by microbes to simultaneously treat wastewater, desalinate water, and produce bioenergy. However, current MDC systems transfer salts to the treated wastewater and affect wastewater's beneficial use. A microbial capacitive desalination cell (MCDC) was developed to address the salt migration and pH fluctuation problems facing current MDCs and improve the efficiency of capacitive deionization. The anode and cathode chambers of the MCDC were separated from the middle desalination chamber by two specially designed membrane assemblies, which consisted of cation exchange membranes and layers of activated carbon cloth (ACC). Taking advantage of the potential generated across the microbial anode and the air-cathode, the MCDC was capable of removing 72.7 mg total dissolved solids (TDS) per gram of ACC without using any external energy. The MCDC desalination efficiency was 7 to 25 times higher than traditional capacitive deionization processes. Compared to MDC systems, where the volume of concentrate can be substantial, all of the removed ions in the MCDC were adsorbed in the ACC assembly double layer capacitors without migrating to the anolyte or catholyte, and the electrically adsorbed ions could be recovered during assembly regeneration. The two cation exchange membrane based assemblies allowed the free transfer of protons across the system and thus prevented significant pH changes observed in traditional MDCs.