High shear enrichment improves the performance of the anodophilic microbial consortium in a microbial fuel cell.
Bottom Line: In many microbial bioreactors, high shear rates result in strong attachment of microbes and dense biofilms.The microbial community of the former, as analysed by DGGE, was significantly different from that of the latter.The results showed that enrichment by applying high shear rates in an MFC can result in a specific electrochemically active biofilm that is thicker and denser and attaches better, and hence has a better performance.
Affiliation: Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Ghent, Belgium.Show MeSH
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Mentions: With a shear rate starting from an estimated level of 80 s−1 for 5 days and increasing every 2 days, the average current generated by the treated MFC increased concomitantly with the increased shear rates up to an estimated level of 120 s−1 (Fig. 1). Above that level, the current started to decrease (Fig. 1A). The total DNA amount of the bacterial cells attached to the electrode changed in a similar pattern (Fig. 1A). The ‘optimal shear rate’ for enrichment was thus determined to be approximately 120 s−1. The MFC was subsequently operated under the condition at which the estimated shear rate was 120 s−1 for 2 weeks to complete the enrichment, before it was operated in default operational mode. Typical current patterns from one of three repeated operations in such a way were shown in Fig. 1B. During the shear stress period, the MFC generated a current of 5.6 ± 0.6 mA versus 2.1 ± 0.2 mA for the control (the low shear enriched MFC) (Fig. 1B). When the high shear stress stopped, the current initially dropped but quickly recovered and subsequently increased to 7.2 ± 0.8 mA (Fig. 1B). The current generated by the high shear enriched MFC at plateau state after the enrichment period reached average values of 6.0 ± 0.5 mA, which is about three times higher than that generated by the low shear enriched MFC (2.0 ± 0.3 mA). Indeed, at plateau state, the high shear enriched MFC could produce a maximum current of 8.1 ± 1.1 mA and a maximum power density of about 160 W m−3 while the low shear enriched MFC could maximally produce 3.0 ± 0.3 mA and about 50 W m−3 (Fig. 2). The chemical oxygen demand (COD) removal efficiency of the high shear enriched MFC was 24 ± 2% and that of the low shear enriched MFC was 20 ± 4%. Using these values and Eq. V, the electron efficiency of the former was calculated to be 25 ± 2% and that of the latter was 10 ± 2%.
Affiliation: Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Ghent, Belgium.