Abstract
Hydrodynamic boundary layer is a significant phenomenon occurring in a flow through a bluff body, and this includes the flow motion and mass transfer. Thus, it could affect the biofilm formation and the mass transfer of substrates in microbial fuel cells (MFCs). Therefore, understanding the role of hydrodynamic boundary layer thicknesses in MFCs is truly important. In this study, three hydrodynamic boundary layers of thickness 1.6, 4.1, and 5 cm were applied to the recirculation mode membrane-less MFC to investigate the electricity production performance. The results showed that the thin hydrodynamic boundary could enhance the voltage output of MFC due to the strong shear rate effect. Thus, a maximum voltage of 22 mV was obtained in the MFC with a hydrodynamic boundary layer thickness of 1.6 cm, and this voltage output obtained was 11 times higher than that of MFC with 5 cm hydrodynamic boundary layer thickness. Moreover, the charge transfer resistance of anode decreased with decreasing hydrodynamic boundary layer thickness. The charge transfer resistance of MFC with hydrodynamic boundary layer of thickness 1.6 cm was 39 Ω, which was 0.79 times lesser than that of MFC with 5 cm thickness. These observations would be useful for enhancing the performance of recirculation mode MFCs.
Highlights
In recent years, the development of renewable energy and electric transportation/storage technologies has begun to flourish due to the consumption and pollution that is caused by fossil fuels [1,2,3]
The voltage of Microbial fuel cells (MFCs)-1 started to rise up by the day 3.5, but MFC-2 and MFC-3 started voltage production 1.5 days later when compared to MFC-1
The voltage of MFC-2 had the similar trend with MFC-1 at day 5, but it did not increase more than MFC-1
Summary
The development of renewable energy (solar energy, wind power, bio-energy, and fuel cell) and electric transportation/storage technologies (supercapacitors) has begun to flourish due to the consumption and pollution that is caused by fossil fuels [1,2,3]. The microbes using electron mediators are not suitable for commercial application as they are planktonic and could be washed out along with the effluent [15], and has higher energy losses than other EET pathways [14]. It obvious that anode biofilm plays a key role in the electricity production of MFCs [16,17], as the bacteria that use direct electron transfer and solid conductive matrix pathway will be attached on the anode electrode
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