Osmotic microbial fuel cell (OMFC) is an emerging technology that can simultaneously treat wastewater and desalinate saline water by taking advantages of microbial respiration with an electrode. In a typical OMFC, a salt chamber (cathode chamber) is separated from an anode chamber using forward osmosis (FO) membrane. Water is drawn through the FO membrane from the anode chamber into the cathode chamber due to the osmotic pressure gradient, thereby diluting the saltwater. In microbial desalination cell (MDC), an alternative to OMFC, the FO membrane is replaced by ion exchange membranes. The salt chamber is separated from an anode chamber with an anion exchange membrane (AEM), and from a cathode chamber with a cation exchange membrane (CEM). Exoelectrogens growing in the anode oxidize organic compounds in the wastewater and donate electrons to the anode electrode to accomplish extracellular respiration. These electrons flow through an external circuit to reduce electron acceptors in the cathode, creating an electric field between the two electrodes. Driven by the electrostatic force, anions and cations in the saline water migrate to the anode and cathode, respectively. As a result, both saline water and wastewater can be treated with negligible energy consumption.
Although MDC and OMFC are promising treatment techniques, they have their own limitations; OMFC achieves dilution instead of salt removal and MDCs are low efficient in desalinating high- salinity water when operated in individual mode. However, a synergetic combination of these two “apparently irrelevant” technologies may potentially complement each other and lead to a sustainable wastewater treatment technology. Therefore, in this study, we propose to construct a single unit of microbial osmotic-electro desalination cell (MO-EDC) by hydraulically linking OMFC (1st module of MO-EDC) to MDC (2nd module of MO-EDC). The 1st module of MO-EDC is used to reclaim water from wastewater and 2nd module is employed to remove salt. The recovered water in the cathode of the 1st module of MO-EDC reduces the conductivity of the saline water that is used both as draw solution and catholyte; meanwhile, wastewater is treated in both anodes of the 1st and 2nd modules of MO-EDC, that provide electrons for electricity generation. The proposed MO-EDC has various advantages like: (i) The strong synergy between OMFC and MDC technologies that may complement each other to overcome the inherent limitations posed by each one; (ii) MO-EDC enables a two stage treatment process that would significantly improve the desalination efficiency and wastewater treatment by collaborating the advantages of both processes through dilution (in the OMFC) and salt removal (in the MDC); (iii) MO-EDC is an energy positive treatment method that can collectively address the water-energy nexus and sustainability.