New insights into the application of microbial desalination cells for desalination and bioelectricity generation

Document Type: Research Paper

Authors

1 Department of Civil and Architectural Engineering, Sultan Qaboos University, P.O. Box 33, Al-Khoud, 123, Muscat, Sultanate of Oman.

2 Department of Petroleum and Chemical Engineering, Sultan Qaboos University, P.O. Box 33, Al-Khoud, 123, Muscat, Sultanate of Oman.

Abstract

Microbial desalination cell (MDC) is considered as a cost-effective substitution to the present energy-intensive desalination methods. Transfer of salt ions through ion exchange membranes towards the counter electrodes takes place through the utilization of self-generated bioelectricity and the concentration gradient. Ions transportation is one of the main challenges faced in MDCs to which less attention has been paid during the course of development. Therefore, new insights into the application of MDCs for efficient utilization of the generated bioelectricity for desalination are of high demand. In light of this, the present research thoroughly investigated the behavior of ions transportation and bioelectricity generation in three MDCs using three different salt solutions; NaCl, synthetic and artificial seawater. The findings obtained suggested that the efficiency of ions transportation and fouling behavior were influenced by salt compositions and concentration of the salt solution. Multivalent ions (i.e. Mg2+, Ca2+, and PO43-) were found more prone to precipitation on the CEM forming a scaling layer, whereas, inorganic deposition and biofouling development were more likely to happen on the AEM. This study also confirmed the occurrence of a significant back diffusion of K+ from catholyte into desalination chamber. Such back diffusion could limit the use of potassium buffer in catholyte in real-scale applications. Moreover, the coefficients of salt transfer and ion diffusion were calculated using mathematical model and Excel solver in three running MDCs. Low salt transfer and ion diffusion coefficients values obtained for all three MDCs could explain the general low performance of MDCs. Further studies are required to optimize the salt transfer and ion diffusion coefficients to boost MDC performance in general; affecting their real-scale implementation.

Graphical Abstract

New insights into the application of microbial desalination cells for desalination and bioelectricity generation

Highlights

  • Ion behavior of three different salt solutions was studied in identical microbial desalination cells (MDCs).
  • Mg2+, Ca2+, and PO43- were major ions resulting in scaling on cation exchange membrane.
  • Inorganic deposition and biofouling were more dominant on anion exchange membrane.
  • Back diffusion of K+ from catholyte to liquid under desalination reduced MDC performance.
  • Increasing bioelectricity generation will boost the rate of ions transportation.

Keywords