Electricity Generation from Artificial Wastewater Using an Upflow Microbial Fuel Cell

TLDR

The upflow microbial fuel cell (UMFC) was developed to generate electricity while simultaneously treating wastewater. The UMFC was operated as an upflow reactor fed with sucrose, using a hexacyanoferrate mediator in the cathode and relying on substrate diffusion, as confirmed by cyclic voltammetry. The UMFC achieved a maximum power density of 170 mW m⁻², with power rising with COD loading up to 2.0 g COD L⁻¹ day⁻¹ before plateauing; internal resistance (84 Ω) limited output, Coulombic efficiencies were low (0.7–8.1 %), yet soluble COD removal exceeded 90 % largely via methanogenic activity.

Abstract

The upflow microbial fuel cell (UMFC) was developed to generate electricity while simultaneously treating wastewater. During a five-month period of feeding a sucrose solution as the electron donor, the UMFC continuously generated electricity with a maximum power density of 170 mW/m2. To achieve this power density, the artificial electron-mediator hexacyanoferrate was required in the cathode chamber. The power density increased with increasing chemical oxygen demand (COD) loading rates up to 2.0 g COD/L/day after which no further increases in power density were observed, indicating the presence of limiting factors. The overarching limiting factor for the UMFC in this study was the internal resistance, which was estimated as 84 Ω at the maximum power density, and restricted the power output by causing a significant decrease in operating potential. Low Coulombic efficiencies varying from 0.7 to 8.1% implied that the electron-transfer bacteria were incapable of converting all of the available organics into electricity, so the excessive substrate created niches for the growth of methanogens. We found that the soluble COD (SCOD) removal efficiencies remained over 90% throughout the operational period, mainly because of methanogenic activity, which accounted for 35 to 58% of the SCOD removed at a loading rate of 1.0 g COD/L/day. Additionally, transport limitation due to insufficient substrate diffusion was shown by cyclic voltammetry (CV).