Acid red 27 biodecolourisation and biogenic electricity generation in stacked microbial fuel cell by citrobacter freundii a1 and enterococcus casseliflavus c1

Abstract

Microbial fuel cell (MFC) is an electrochemical system which utilises microorganisms to generate electricity via its catalytic activities. Recently, the capability of MFC in generating electricity has been assimilated with wastewater treatment as an alternative approach for a sustainable and eco-friendly technology. Although the MFC has the potential to be synchronised with both the wastewater treatment and electricity generation application, the amount of electricity generated from this technology is still insufficient. This study employed Citrobacter freundii A1 and Enterococcus casseliflavus C1 bacterial consortia that have been previously isolated and identified in the assessment of azo dye biodecolourisation and biogenic electricity generation in dual-chamber salt bridge MFC. Initially, the feasibility of sequential facultative anaerobic-aerobic treatment for complete dye degradation was evaluated using Acid Red 27 (AR-27) dyes where 98% decolourisation was achieved using 0.5 g/L glucose and 1.0 g/L nutrient broth as co-substrates under static condition for the non-MFC study. Ultra Violet-Visible spectroscopy and Fourier Transform Infrared (FTIR) spectroscopic analyses confirmed that the azo linkage was cleaved after the decolourisation occurred. The cyclic voltammetry analyses also showed that the decolourisation of AR-27 by C. freundii A1 and E. casseliflavus C1 was an electrochemically irreversible reaction while the detection of oxidation reaction during aerobic treatment proved that the process of mineralisation took place. The degradation of AR-27 was also confirmed by the decrease in catechol concentration detected through High-Performance Liquid Chromatography (HPLC) analysis. Simultaneous electricity generation and wastewater treatment were conducted by connecting two individual MFC in parallel with optimised 5000 O external resistance and 3.0 M sodium chloride salt bridge concentration. The maximum voltage recorded by the open circuit voltage and close circuit voltage was 595 mV and 84 ± 15 mV, respectively. While the power and current density generated by the optimised MFC system was 10.15 ± 2 mA/m2 and 0.86 ± 0.3 mW/m2. The use of higher concentration of sodium chloride salt bridge and parallel configuration in MFC was able to improve the MFC performance by generating higher current and output power. Scanning Electron Microscope image and bacterial cell number analysis revealed the surface morphology and biofilm development during the MFC operation with the adhesion of microorganisms on the electrode surface. Besides, FTIR analysis on the MFC electrode after operation also showed the presence of biofilm with the detection of extracellular polymeric substances (EPSs) functional groups on the electrode surface. In conclusion, C. freundii A1 and E. casseliflavus C1 consortium has the potential to be used in simultaneous azo dye wastewater treatment and biogenic electricity generation using the MFC technologies.