Enhanced performance of microbial fuel cell at low substrate concentrations by adsorptive anode

• GAC-MFC delivered much better performance than GG-MFC at low COD concentrations.
• Increasing circulation flow rate caused more improvement in GAC-MFC’s performance.
• GAC adsorption greatly promoted anode mass transfer at low COD concentrations.
• GAC adsorption helped to mitigate the impact of COD concentrations’ perturbation.

In this study, a microbial fuel cell (MFC) with granular activated carbon packed anode (GAC-MFC) is developed and compared with a MFC with granular graphite packed anode (GG-MFC), to evaluate the adsorptive effect of the granular activated carbon anode on MFC’s performance. The current output of GAC-MFC (11.1 mA, 18.1 mA and 21.6 mA) is much higher than that of GG-MFC (4.87 mA, 12.5 mA and 17.9 mA) at low substrate COD concentrations (∼50, ∼100 and ∼200 mg/L) when a low external resistance (20 Ω) and high circulation flow rate (20 mL/min) are applied. The half-saturation constant (Ks) of GAC-MFC is about half as much as that of GG-MFC, suggesting that GAC-MFC has more affinity for anode substrate and deliver better kinetic performance than GG-MFC. Internal resistance distribution shows that mass diffusion resistance of GAC-MFC is at least 50% lower than that of GG-MFC when the substrate COD is ∼50 mg/L, indicating that the adsorptive effect of granular activated carbon packed anode helps to effectively facilitate mass transfer at low COD concentrations. Otherwise, the substrates adsorbed on GAC surface also serve to buffer the impact of COD concentration plummeting in bulk solution.

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