Practical Guidance for Maximizing Microbial Fuel Cells Performance in Real Industrial Wastewater Treatment using Integrative Engineering Optimization and Metagenomics Analysis

Microbial fuel cells (MFCs) are eco-friendly technologies allowing the conversion of both organic and inorganic substances in wastewater to electricity.  While conceptually promising, several challenges exist regarding the performance and stability of MFCs in real industrial settings.  To address the gap, this work investigated the influence of operational settings of MFCs used for treating sulfide-rich wastewater from a canned pineapple factory regarding the hydraulic retention time (HRT) and organic loading rate (OLR) on the MFC performance.  Through optimization, a current density generation of 47±15 mA/m², a COD removal efficiency of 91±9%, and a sulfide removal efficiency of 86±10% were achieved.  To reveal the microbial community as a key biological engine determining the high MFC performance, a metagenomics study based on 16S rRNA gene amplicon sequencing was performed.  A total of 14 DNA samples, including inoculum sludge, anaerobically treated pineapple wastewater as the MFC influent, anode-attached samples, and MFC reactor suspension, were collected. Based on differential microbial abundance and microbial association analysis, microbes supporting MFC performance were identified. Finally, the guidance for achieving the effective MFC in the real industrial wastewater treatment was proposed: (i) the microbial inoculum is important in setting up the strong microbial community, (ii) initiating the MFC operation with the proper OLR helps in forming a robust and effective microbial community capable of adapting to the unexpected conditions from factory production, and (iii) MFC-supporting microbes should be retained to sustain MFC performance.  This includes maintaining a high composition of electrogenic bacteria (i.e., Clostridium (OTU00515)), sulfide-oxidizing bacteria (i.e., Hydrogenophilaceae (OTU00713 and OTU01182), Candidatus Chlorothrix (OTU01036)), and methanotrophs (i.e., Methylocaldum (OTU00318 and OTU00322), Candidatus Methylospira (OTU00717)), while limiting the activity of sulfate-reducing bacteria (i.e., Acinetobacter (OTU00138)), and methanogens (i.e., Methanolinea and Methanosaeta). Understanding the MFC performance and microbial activity relationship is vital for successful MFCs in real industrial applications.