Development of microbial fuel cell prototypes for domestic wastewater treatment and electricity generation

Abstract

Efficient domestic wastewater treatment systems are necessary to meet good effluent standards. Adhering to effluent standards is vital for protecting public health by preventing the spread of waterborne diseases and ensuring safe drinking water. It also helps safeguard ecosystems by limiting pollutants that can harm aquatic life and degrade biodiversity. While effluent standards set limits on pollutants, they may not fully account for the complexities of environmental impact, as some harmful substances can still persist at allowable levels. Therefore, beyond simply meeting these standards, removing physical and chemical pollutants is critical for minimising long-term environmental damage, protecting ecosystems, and ensuring water safety. However, this is not the case in most domestic wastewater treatment plants in Zimbabwe. It therefore crucial to introduce sustainable, innovative and environmentally friendly wastewater treatment systems that ensure efficient wastewater treatment. The aim of this study was to design and fabricate microbial fuel cell prototypes for domestic wastewater treatment with the goal of achieving simultaneous wastewater treatment and energy generation in Zimbabwe. The study focused on four MFC prototypes: Single Chamber Activated Carbon Cathode (SCAC), Single Chamber Biochar Cathode (SCBC), Double Chamber Activated Carbon Cathode (DCAC), and Double Chamber Biochar Cathode (DCBC). The research aimed to assess the effectiveness of these prototypes in reducing wastewater parameters; Chemical Oxygen Demand (COD), Total Dissolved Solids (TDS), Electrical Conductivity, Grease and oils, phosphorous, potassium, and nitrogen, while evaluating their electricity generation capabilities. Experimental results indicated that all MFC prototypes achieved significant COD removal (p = 0.03) with removal efficiencies of 75% (SCAC), 82%, (SCBC), 83% (DCAC) and 95% (DCBC) demonstrating their efficacy in wastewater treatment. Among the prototypes, SCBC and DCBC exhibited superior performance in reducing COD, phosphorous, and potassium, attributed to their mesoporous structures that enhance microbial activity. However, all prototypes struggled with reducing grease, oils, electrical conductivity, and total dissolved solids (TDS) (p> 0.05), largely due to biofouling and suboptimal electrode materials. In terms of electricity generation, SCAC prototypes consistently outperformed SCBC prototypes and showed better voltage (maximum voltage 163 mV and 46 mV respectively) and current production (maximum current 240 μA and 51 μA respectively). DCAC prototypes consistently outperformed DCBC prototypes though DCBC had a maximum recorded voltage and iii current greater than DCAC prototypes (maximum voltage 504 mV and 528 mV respectively) and current production (maximum current 669 μA and 776 μA respectively). Single Chamber MFCs generally produced higher and more stable electrical outputs compared to Double Chamber MFCs, which faced higher internal resistance and instability. Energy conversion efficiency was notably low across all prototypes (less than 6%), with Double Chamber MFCs demonstrating marginally higher efficiency than Single Chamber MFCs. The study demonstrated that MFC prototypes, particularly SCBC and DCBC, are effective in wastewater treatment, achieving significant reductions in COD, phosphorous, and potassium. However, all prototypes exhibited limitations in removing grease, oils, TDS, and electrical conductivity, as well as low energy conversion efficiency. While these results show potential for MFCs in wastewater treatment, their practical application at a large scale remains limited due to inefficiencies in energy generation and operational challenges such as biofouling. Further research is necessary to optimise MFCs for large-scale use, focusing on improving energy efficiency, stability, and long-term viability