Microbial Desalination Cell Combined with Capacitive Deionization/Membrane Capacitive Deionization to Desalinate Seawater

Abstract

Microbial desalination cell (MDC) was considered inefficient to desalinate salt water with low salt concentration, therefore, the feasibility of using capacitive deionization (CDI) and membrane capacitive deionization (MCDI) as a post-processing technologies for MDC was investigated in this study, as well as the possibility of using MDC as the power supply for CDI and MCDI. The internal resistances of MDC with different salt concentration, the desalination rate and fresh water yield during a typical desalination cycle under initial salt concentration of 35 g/L were investigated in order to find out the deadline salt concentration for the MDC to desalinate effectively. The internal resistance increased from 21.7 to 602 Ω as the concentration of salt water decreased from 35 g/L to 0.1g/L. The salt water volume increased from 42 to 48 ml when the salt concentration decreased from 35 to 15 g/L, then decreased to 38 ml at the end of one desalination cycle when the salt concentration achieved 0.05 g/L due to the salt gradient (osmotic pressure). The maximum desalination rate during one typical desalination cycle in our experiment reached 5.65 mg/h when salt concentration decreased from 27.26 to 26.32 g/L, while the minimum desalination rate was 0.534 mg/h when salt concentration decreased from 0.38 to 0.05 g/L. It was concluded that MDC was not suitable to desalinate salt water with salt concentration less than 1 g/L. When CDI and MCDI were used as the post-processing technologies for MDC, a better performance in term of electrosorption capacity was obtained from MCDI with an influent salt concentration of 1 g/L. The experimental result also showed that the electrosorption capacity of MCDI with MDC as power supply was more than that with potentiostat as power supply at 0.8V, this suggests that MDC could be an alternative power supply for MCDI.