(Invited) An Integrated Microbial Desalination Cell-Driven Capacitive Deionization System as an Electrochemical Means for Wastewater Treatment, Electricity Generation and Desalination

Abstract

Due to unstainable use of natural water resources, alternative water resources such as brackish water and seawater desalination have been an emerging solution. However, development of desalination capacity is limited due to the high energy requirements for removing salt ions from water. Currently, capacitive deionization technology (CDI), following the working principle of supercapacitors, has attracted considerable attention from academia, industry, and government agency. As compared to conventional desalination technologies, CDI has several advantages including low energy consumption, easy regeneration, high water recovery, and no secondary waste. In CDI, by applying an external electric filed between two parallel of nanoporous carbon electrodes (i.e., carbon aerogel, activated carbons, carbon nanotubes, and graphene), ions can be stored at the electrode/solution interface via electrical double layer (EDL) formation. Additionally, microbial desalination cell (MDC) is a new bioelectrochemical technology for seawater desalination with simultaneous electricity generation and wastewater treatment. Basically, a MDC reactor contains an anode chamber, a desalination chamber, and a cathode chamber. In MDC, microorganisms can oxidize organic waters in wastewater to harvest electric energy, and meanwhile, salt ions can be removed during the electricity generating process. In this study, we propose a hybrid electrochemical desalination system for seawater desalination by coupling CDI device with a MDC reactor. As a result, MDC produced electricity with open circuit voltage of 0.8 V and a current of 3 mA by using bacteria to degrade organic contaminants through anode bacterial oxidation and cathode reduction. In MDC, 91% removal of chemical oxygen demand (COD) in synthetic wastewater can be achieved, and the solution conductivity can be reduced from 17,000 µS/cm to about 200 µS/cm. More importantly, CDI device can be driven by electricity harvesting from the two MDCs in parallel, and as the downstream desalination process to further desalinate salt water. The results of this study can demonstrate the feasibility of the integrated electrochemical MDC-CDI system for simultaneous wastewater treatment, power production, and water desalination. .