Improving water desalination by hydraulically coupling an osmotic microbial fuel cell with a microbial desalination cell

A system consisting of two membrane-based bioelectrochemical reactors was developed to treat artificial wastewater and desalinate saline water. In this system, an osmotic microbial fuel cell (OsMFC) containing a forward-osmosis (FO) membrane was hydraulically coupled with a microbial desalination cell (MDC) that had ion exchange membranes. The coupled system significantly improved desalination efficiency through both dilution (in the OsMFC) and salt removal (in the MDC), and achieved more organic removal than an individual MDC. It was found that the high-power operation mode was more suitable for the OsMFC than the open-circuit mode and the high-current mode, because of good desalination performance (95.9% conductivity reduction in the coupled system) and energy production (0.160kWh/m³ treated saline water). When the active layer of the FO membrane was facing the feed solution, more water flux was obtained than the reversal membrane orientation. The coupled system achieved high reduction of conductivity (>85%) from the salt solution containing 10-50g NaCl/L. The acidified water was more advantageous as a catholyte for the MDC because of the superior desalination performance. These results have collectively demonstrated the feasibility of a membrane-based bioelectrochemical system for simultaneous wastewater treatment and saline water desalination.