Comparison of biological catholyte to chemical catholyte in microbial desalination cells

Abstract

Abstract. Microbial fuel cells (MFCs) can be used for electricity generation. The need for an economic way to reclaim fresh water from seawater is growing in many parts of the world. Modification of microbial fuel cells into desalinating microbial fuel cells is an effort to enhance utility of this technology. This study examines adding a middle, third, desalination chamber to a standard two-chambered microbial fuel cell. Biological and chemical catholytes were compared for desalination and power generation efficiency. Successful results have been obtained in three chamber desalinating microbial fuel cells (MDCs). Rumen microorganisms have been used as exoelectrogens in the MFC's anodic chamber. Glucose was employed as substrate. Nanochloropsis salina, a type of marine algae, and potassium ferricyanide (KFe(CN)6) were used in the cathodic chamber. The central, desalination chamber contained synthetic sea water composition. The system was operated in fed batch mode. Biomass, measured in terms of protein content and chemical oxygen demand (COD), was monitored to maintain the operating conditions. Power generation and desalination were monitored to compare the efficiency of catholytes. The observations revealed that the chemical catholyte generated higher power than biocatholyte while desalination efficiency when using a biocatholyte was higher than for the chemical catholyte. Power generation at the rate of 1532 mW/m3 and 384 mW/m3 with 41 and 43 % desalination after 24 hours was obtained for the potassium ferricyanide and marine algae catholyte systems respectively. Obtained results suggested that MDCs can be used for partial desalination. Desalination efficiency can be improved by changing the seawater to anolyte ratio and running the system in continuous mode.