Simultaneous power generation and wastewater treatment in the single chamber air cathode microbial fuel cell have been enhanced by introducing wild-type Klebsiella variicola as an efficient inoculum for the anode operated with palm oil mill effluent.

Anodic biofilm plays a crucial role in bioelectrochemical system to make it sustainable for long-term performance. However, the accumulation of dead cells over time within the anode biofilm can be particularly detrimental for current generation. In this study, the effect of ultrasound on anode biofilm thickness was investigated in microbial fuel cells (MFCs). Ultrasonic treatment was employed for different durations to evaluate its ability to control the thickness of the biofilm to maintain stable power generation. Cell viability count and field emission scanning electron microscopy (FESEM) analysis of the biofilms over time showed that the number of dead cells increased with the increase of biofilm thickness, and eventually exceeded the number of live cells by many-fold. Electrochemical impedance spectroscopy (EIS) analysis indicated that the high polarization resistance appeared due to the dead layer formation, and thus the catalytic efficiency was reduced in MFCs. The stable power generation was achieved by employing ultrasonic treatment for 30 min every 6 days with some initial exception. The low frequency ultrasound treatment successfully dislodged the ineffective biofilm from the surface of the anode. Moreover, the ultrasound could increase the mass transfer rate of the nutrients and cellular waste through the biofilm leading to the increase in cell growth. Therefore, ultrasonic treatment is verified as an efficient method to control the thickness of the biofilm as well as enhance the cell viability in biofilm thereby maintaining the stable power generation in the MFC.

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In this work, manganese dioxide/carbon nanotube (MnO2/CNT) have been synthesized by sonochemical‐coprecipitation method and demonstrated that it could be an effective electrocatalyst for oxygen reduction reaction (ORR). Moreover, the effect of CNT inclusion with MnO2 was also investigated for ORR. The physical and electrochemical properties of the MnO2/CNT were examined by powder X‐ray diffraction (XRD), Fourier Transform Infrared (FT‐IR) spectroscopy, Brunauer‐Emmett‐Teller (BET), Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy/Energy Dispersive X‐ray (FESEM/EDX), Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), Mott‐Schottky and Rotating Disk Electrode (RDE) analysis. CV showed higher currents for the ORR in MnO2/CNT than CNT; however, ORR current dropped when the MnO2 loading was increased from 20–40 %. The EIS analysis showed that charge‐transfer resistance for MnO2/CNT was significantly lower compared to the MnO2 indicating that MnO2 has good contact with CNT and the composite possess high electrical conductivity. Mott‐Schottky results demonstrated that incorporation of CNT into MnO2 resulted in producing larger electron density in n‐type MnO2/CNT compared to MnO2 which is liable for efficient electron donation from the Mn3+ to adsorbed oxygen in the rate determining step. RDE results showed that MnO2/CNT follows 4e− transfer pathway, indicating its ability to act as an effective ORR electrocatalyst.

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