A New Method for Water Desalination Using Microbial Desalination Cells

Abstract

Current water desalination techniques are energy intensive and some use membranes operated at high pressures. It is shown here that water desalination can be accomplished without electrical energy input or high water pressure by using a source of organic matter as the fuel to desalinate water. A microbial fuel cell was modified by placing two membranes between the anode and cathode, creating a middle chamber for water desalination between the membranes. An anion exchange membrane was placed adjacent to the anode, and a cation exchange membrane was positioned next to the cathode. When current was produced by bacteria on the anode, ionic species in the middle chamber were transferred into the two electrode chambers, desalinating the water in the middle chamber. Proof-of-concept experiments for this approach, using what we call a microbial desalination cell (MDC), was demonstrated using water at different initial salt concentrations (5, 20, and 35 g/L) with acetate used as the substrate for the bacteria. The MDC produced a maximum of 2 W/m2 (31 W/m3) while at the same time removing about 90% of the salt in a single desalination cycle. As the salt was removed from the middle chamber the ohmic resistance of the MDC (measured using electrochemical impedance spectroscopy) increased from 25 Omega to 970 Omega at the end of the cycle. This increased resistance was reflected by a continuous decrease in the voltage produced over the cycle. These results demonstrate for the first time the possibility for a new method for water desalination and power production that uses only a source of biodegradable organic matter and bacteria.

Development of Bioelectrochemical Systems to Promote Sustainable Agriculture

“…To maintain electroneutrality, the electric potential gradient generated by exoelectrogenic bacteria drives cations and anions in the saline solution to migrate through CEM and AEM into the cathode chamber and anode chamber, respectively [81], thereby achieving desalination. The proof-of concept of MDC was firstly proposed by Cao et al [7], and the technology has been advanced through both fundamental research and system development [7,82,83]. Because of the low desalination rate of MDC [84], two potential application niches have been identified.…”

“…Bacterial dissimilatory metal reduction (BDMR) has been regarded as the process closest to electrode respiration [2], with the Geobacter and Shewanella species identified as the most common BDMR model bacteria used in BES [4]. Development of BES can be classified into the following categories based on their application purposes: microbial fuel cells (MFC) [5], microbial electrolysis cells (MEC) [6], microbial desalination cells (MDC) [7], microbial electrosynthesis cells (MES) [8], etc. BES can be applied not only to treat the waste but also to harvest energy and value-added products.…”

Microbial fuel cells for energy production from wastewaters: the way toward practical application

“…For industrial wastewaters with high salinity, it would be attractive to integrate MFCs with the electrodialysis technique to form microbial desalination cells (MDCs) (Cao et al, 2009;Chen et al, 2011;Jacobson et al, 2011), which can simultaneously remove ionic species and generate electricity from the wastewater. A MDC is constructed by incorporating one or several pairs of anion exchange membrane (AEM) (next to the anode) and cation exchange membrane (CEM) (by the cathode) in a MFC (Cao et al, 2009).…”

“…A MDC is constructed by incorporating one or several pairs of anion exchange membrane (AEM) (next to the anode) and cation exchange membrane (CEM) (by the cathode) in a MFC (Cao et al, 2009). Wastewaters of high salinity are injected into the chamber between the membranes and those with low salinity into the anode and cathode chambers.…”

Bioelectricity inhibits back diffusion from the anolyte into the desalinated stream in microbial desalination cells

“…With anion exchange membrane (AEM) and cation exchange membrane (CEM) installed between the anode and the cathode, an MDC takes advantage of the electrical field generated by anode microbial metabolism and cathode (oxygen) reduction reaction to separate ions in salt solution between the two ion-exchange membranes (Cao et al, 2009). The mechanism of ion separation in an MDC is similar to that of electrodialysis (ED), but its driving force is the energy extracted from organic matters in wastewater by microorganism in the anode.…”