Bioelectricity generation and analysis of anode biofilm metabolites from septic tank wastewater in microbial fuel cells

Abstract

The microbial fuel cell (MFC) has gained interest among the scientific community due to the feasibility of transforming organic wastes directly into electrical energy through biocatalysis or enzymatic bioelectrochemical reactions. In the present study, an effective coculture system, namely, Serratia marcescens AATB1 and Klebsiella pneumoniae AATB2, was used in the MFC system. The isolated strains, AATB1 and AATB2 were identified as biofilm producing bacteria. The experiments were performed in a two-chambered MFC setup with septic tank wastewater as the substrate in a 5 days batch mode. Pure culture of S. marcescens AATB1 and K. pneumoniae AATB2, and their cocultures were able to produce energy with the maximum current densities of 728.85 ± 36 mA/m2, 642.19 ± 32 mA/m2 and 869.11 ± 43 mA/m2, respectively, and the maximum power densities of 341.65 ± 17 mW/m2, 257.51 ± 12 mW/m2 and 398.69 ± 19 mW/m2, respectively. During the process, cyclic voltammetry analysis has revealed the electrochemical behavior of the anodic biofilm. Approximately, 70.42% ± 3.52% of chemical oxygen demand removal was achieved during the process. Biofilm formation by the adhesion of microbes on the electrode surfaces was visualized by confocal laser scanning microscope and scanning electron microscope. All the three MFC systems were produced by biofilms containing extracellular polymeric substance from S. marcescens AATB1 (55 ± 2.75 μg/cm2 of protein, 61 ± 3.05 μg/cm2 of carbohydrate) and K. pneumoniae AATB2 (46 ± 2.30 μg/cm2 of protein, 53 ± 2.65 μg/cm2 of carbohydrate) and coculture (60 ± 3.00 μg/cm2 of protein, 69 ± 3.45 μg/cm2 of carbohydrate). Furthermore, the anode biofilm metabolites were identified by Gas Chromatography–Mass Spectrometry (GC-MS) and Nuclear Magnetic Resonance NMR spectroscopy.