Effect of initial salt concentrations on cell performance and distribution of internal resistance in microbial desalination cells

Abstract

Microbial desalination cells (MDCs) are modified microbial fuel cells (MFCs) that concurrently produce electricity and desalinate seawater, but adding a desalination compartment and an ion-exchange membrane may increase the internal resistance (R_i), which can limit the cell performance. However, the effects of a desalination chamber and initial NaCl concentrations on the internal resistances and the cell performances (i.e. Coulombic efficiency (CE), current and power density) of MDCs have yet to be thoroughly explored; thus, the cell performance and R_i distributions of MDCs having different initial concentrations and an MFC having no desalination chamber were compared. In the MDCs, the current and power density generation increased from 2.82 mA and 158.2 mW/m² to 3.17 mA and 204.5 mW/m² when the initial NaCl concentrations were increased from 5 to 30 g/L, as a consequence of the internal resistances decreasing from 2432.0 to 2328.4 Ω. And even though the MFC has a lower R_i than the MDCs, lower cell performances (current: 2.59 mA; power density: 141.6 mW/m² and CE: 62.1%) were observed; there was no effect of improved junction potential in the MFC. Thus, in the MDCs, the higher internal resistances due to the addition of a desalination compartment can be offset by reducing the electrolyte resistance and improving the junction potential at higher NaCl concentrations.

Keywords:

• desalination
• electricity generation
• initial NaCl concentration
• internal resistance
• microbial desalination cells

Acknowledgement

This work was supported by a grant (07SEAHEROA01-01) from the Plant Technology Advancement Program funded by the Ministry of Land, Transport and Maritime Affairs, Korea.