The Combination Of Microbial Desalination Cell With Capacitive Deionization To Desalinate Salt Water

Microbial desalination cell (MDC) was developed in2009as a new desalinationtechnique. Because of its low energy consumption, MDC has received great attention.However, when MDC was used to desalinate salt water with low salt concentration, theperformance of the desalination was limited by a sharply increase of internal resistanceof MDC which leads to a decrease of desalination rate and energy output. Therefore,capacitive deionization (CDI) and membrane capacitive deionization (MCDI) wereproposed as the post-processing technologies for MDC in this study.This subject focused on the optimization of the CDI and the combination of MDCand CDI to desalinate salt water, as well as the possilibity of using MDC to power CDIand MCDI. The fabrication condition of the electrodes and the operating conditions forCDI were optimized in order to get a good electrosorption performance.Powdered activated carbon was used to fabricate electrodes for CDI, and it wasconcluded that when chemically inactive material such as carbon paper was used as thecurrent collector for CDI, a stable electrosorption performance could be achieved. Whenthe mass fraction of carbon black was10%, a relative low internal resistance and highspecific capacitance of the electodes could be achieved. The elecrosorption performanceof CDI was not improved when powdered activated carbon was chemically treated byHF and NH3·H2O. A relatively preferable electrosorption performance could beachieved when the applied voltage was1.5V and the operating velocity was25mL/min.It was concluded that membrane capacitive deionization (MCDI) performed better thanCDI expecially when salt water of high salt concentration was desalinated.The internal resistances, fresh water yield and average desalination rates duringduring one desalination cycle of MDC were measured, it was concluded that MDC wasnot suitable to desalinate salt water with a concentration less than1g/L. MCDI was usedas a downstream technique for MDC. The experiments results suggested that it ispossible to use MDC as the power supply for MCDI and the electorsorption capacity ofMCDI was more than that with the potentiostat as the power supply with the samevoltage as the open-circuit voltage of the single MDC. In order to limit the impact ofpower output of MDC on the electrosorption performcance, two MDCs operated inseries and parallel were applied as the power supply for MCDI. The results showed thatwhen two MDCs were operated in parallel, the electrosorption performance was improved.