Electricity generation by Pseudomonas aeruginosa ZH1 in microbial fuel cell using palm oil mill effluent

Abstract

Microbial fuel cell (MFC) is a bioelectrochemical system that is recognised as a promising source of renewable energy. Electro-active bacteria are used to generate electricity in MFC, either as pure or mixed culture. Recent studies have shown that MFC is capable of utilising various types of wastewaters as the substrate for electricity generation. In view of this, the investigation on the feasibility of pure bacterial culture for electricity generation in a double-chambered MFC using final discharge palm oil mill effluent (POME) was carried out. The physical enhancement method was used to isolate electro-active bacteria from POME sludge grown on the anode of MFC. The isolate was identified and designated as Pseudomonas aeruginosa ZH1 using the 16S rRNA gene sequence analysis. The maximum power density and current density generated in MFC using P. aeruginosa ZH1 were 451.26 ± 22.97 mW/m2 and 654.90 ± 17.12 mA/m2, respectively. The high electricity generation was contributed from the self-produced pyocyanin which acted as the electron mediator. Analysis on the biochemical and physical factors affecting the MFC performance showed that P. aeruginosa ZH1 could not achieve high electricity generation and efficient treatment of POME simultaneously in MFC. Significant electricity generation was achieved at initial anode pH 9, external resistance of 500 Ω, 10% (v/v) inoculum size, under facultative anaerobic condition, undiluted POME as the substrate, using graphite felt as the electrodes with a surface area of 24.84 cm2 and the addition of pyruvate and yeast extract in the anode. Furthermore, the time-course characterisation method was conducted to analyse the performance of MFC at 4, 24, 72 and 120 hours, respectively under batch mode operation. The maximum power generation and polarisation curve indicated that the optimum MFC performance was achieved at 72 hours. This was in correlation with the optimum biofilm development at 72 hours as observed from the bacterial concentration, microscopic imaging and Fourier Transform Infra-Red spectroscopy (FTIR) analysis. The long term MFC performance was investigated under sequential batch mode for 25 days at five days/cycle. The addition of pyruvate and yeast extract increased the electricity generation in which the maximum power density and current density were achieved during the second cycle at 33.51 ± 30.35 mW/m2 and 153.40 ± 68.90 mA/m2, respectively. Microscopic and elemental analysis revealed that the developed biofilm consists of web-like structures which could represent bacterial nanowires for extracellular electron transfer. In conclusion, this study demonstrated that P. aeruginosa ZH1 is a suitable electro-active bacteria for the generation of electricity in MFC using final discharge POME.