Performance Evaluation of Microbial Fuel Cell Operated with Pd or MnO₂ as Cathode Catalyst and <i>Chaetoceros</i> Pretreated Anodic Inoculum

Abstract

A microbial fuel cell (MFC) is a bioelectrochemical system that can recover bioelectricity from wastewater, with simultaneous organic matter removal from the wastewater. However, due to the inferior power production of MFCs and the higher fabrication cost, successful field-scale demonstration of this novel technology is still to be accomplished. Power production of MFCs can be improved by employing a cathode catalyst to overcome the sluggish oxygen reduction reaction (ORR) on bare carbon-based electrodes. In this regard, to enhance the power generation in a MFC, three MFCs inoculated with marine algae Chaetoceros pretreated mixed bacterial culture were operated with different cathode catalysts. To examine the effect of cathode catalyst on power generation, Pd and MnO2 were used as cathode catalysts in the MFC-Pd and MFC-Mn, respectively, while the third MFC (MFC-C) was devoid of any catalyst. The chemical oxygen demand (COD) removal efficiency was estimated to be 63.3% ± 1.83%, 62.8% ± 2.15%, and 61.3% ± 1.76% for MFC-C, MFC-Mn and MFC-Pd, respectively. The MFC-Pd exhibited highest coulombic efficiency of 25.82% ± 2.1%, followed by MFC-Mn (17.47 ± 1.6%) and MFC-C (10.68% ± 2.8%). The power density of MFC-Pd, MFC-Mn, and MFC-C was estimated to be 63.94, 27.12, and 10.46 mW/m2, respectively. The results exhibited that the application of Pd as a cathode catalyst yields higher power in a MFC. Furthermore, the maximum power density of MFC-Mn, with MnO2 as cathode catalyst, was 2.36 fold lesser than that obtained from the MFC-Pd and 2.59 times higher than MFC-C. In addition, the wastewater treatment efficiency measured in terms of COD removal efficiency was similar for all the MFCs given that similar operating conditions (Chaetoceros pretreatment on the anodic inoculum) were maintained in the anodic chamber of all these MFCs. However, as MnO2 is a low-priced material, the energy recovered per dollar spent on the catalyst is six times higher for MnO2 than for Pd. Thus, the combination of MnO2 as cathode catalyst and Chaetoceros as a methanogenesis inhibitor demonstrated a low-cost, sustainable solution for power enhancement in MFCs.