Removal of Cd and Ni with enhanced energy generation using biocathode microbial fuel cell: Insights from molecular characterization of biofilm communities

Abstract

The present study explores the potential of using biocathode for enhanced energy recovery from wastewater and removal of toxic metals Cd and Ni from aqueous solutions in a double chamber Microbial Fuel Cell (MFC) overcoming the challenge of their less favoured removal owing to low redox potential. Wetland sediment was used as inoculum both in anode and cathode chambers. Power density generated by biocathode MFC from diluted distillery wastewater was 722 mW/m3, which was 10 times that produced by the abiotic MFC. At 10 mgL−1 concentration, 92% Ni and 87% Cd were removed, while at 25 mgL−1 concentration, removal increased by 70% when biocathode was used. Microbial characterization of biofilms, using 16S metagenomic sequencing revealed that diversity of microbial communities developed on the anode and cathode biofilms were quite different though inoculum source was the same. Metal tolerant γ-proteobacteria, exopolysaccharide producing and metal chelating genera like Ochrobactrum and Halomonas were abundant in cathodic biofilm that seem involved in Ni and Cd removal. Anodic biofilm was mostly dominated by the orders Clostridiales and Burkholderiales (class β-proteobacteria), and the fermentor genus Achromobacter was dominant. The novel approach of using biocathode in the MFC, thus significantly improved the removal of Ni and Cd from single as well as mixed metal solutions along with remarkable increase in energy recovery without any use of expensive catalysts, and characterisation of the biofilm at anode and cathode indicated how the microbial communities originating from same inoculum differed in their composition perform different roles of electricity production and metal removal in the MFC.