BACKGROUND: Many approaches have been employed to increase the understanding and consequently the performance of microbial fuel cells to obtain simultaneous power production and biodegradation. This study uses recombinant Escherichia coli K-12 with MtrA, MtrC and MtrCAB inserts previously prepared using synthetic biology to evaluate the involvement of each of these genes in bioenergy production and biodegradation of Congo red using a double chamber microbial fuel cell.
RESULTS:MtrC was the key gene required for energy production corresponding to an average voltage of 360 mV (external resistance 1 k ) and power density of 59 mW m -2 , while E. coli with MtrCAB insert showed the highest decolourisation which reached 80% in 36 h under microbial fuel cell conditions. Coulombic efficiency was 1.2% for E. coli with MtrCAB compared with 2.5% and 2.3% for MtrC and MtrA inserts, respectively. Riboflavin seems to be involved in the electron transferring, its concentration was highest for E. coli with MtrA insert despite its poor performance for both bioenergy production and dye degradation.CONCLUSION: This study suggests that electrons are mutually exclusive between electricity production, dye degradation and other cellular activities. This study helps to improve our understanding of the dual bioenergy/decolourisation process taking place in MFCs in order to maximize the outcome.
Electrochemical measurementsVoltage output data were collected using a Picolog ADC-24 (PicoTechnology, UK) online data logging system, Cambridgeshire. Polarisation tests were done by connecting different values of external resistance once voltage had stabilized. Coulombic efficiency (CE) was calculated according to Fernando et al. 14
COD testsThe chemical oxygen demand removal was determined using the closed reflux titrimetric method as described by Westwood. 16 COD was calculated as follows:
Abstract:9 Dissimilatory metal reducing bacteria can exchange electrons extracellularly and hold great 10 promise for their use in simultaneous wastewater treatment and electricity production. This study
Objectives\ud
To investigate the contribution of direct electron transfer mechanisms to electricity production in microbial fuel cells by physically retaining Shewanella oneidensis cells close to or away from the anode electrode.\ud
Results\ud
A maximum power output of 114 ± 6 mWm−2 was obtained when cells were retained close to the anode using a dialysis membrane. This was 3.5 times more than when the cells were separated away from the anode. Without the membrane the maximum power output was 129 ± 6 mWm−2. The direct mechanisms of electron transfer contributed significantly to overall electron transfer from S. oneidensis to electrodes, a result that was corroborated by another experiment where S. oneidensis cells were entrapped in alginate gels.\ud
Conclusion\ud
S. oneidensis transfers electrons primarily by direct electron transfer as opposed to mediated electron transfer
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