Temperature-driven changes in biofilm formation and electrochemical performance of deep-sea inoculum in microbial fuel cells

Abstract

Microbial fuel cells (MFCs) generate electricity by converting organic materials and utilizing electroactive bacteria, where anodic biofilms play a vital role in electron transfer and controlling internal resistance. The adaptation of deep-sea microbial communities to diverse environmental conditions, particularly the effects of temperature on biofilm formation and MFC efficiency in high-salinity environments, remains under-explored. This study aims to fill this gap by examining how different temperatures (4 °C (F35), 25 °C (R35), and 37 °C (I35)) affect anodic biofilm formation and MFC performance. The research employs deep-sea sediment inoculum from the South China Sea to enhance understanding of microbial adaptability and optimize performance in extreme conditions. Among the tested conditions, I35 demonstrated the highest current and power densities at 172.49 mA/m² and 20.09 mW/m², representing increases of approximately 129 % and 350 % compared to F35. R35 displayed moderate output. Microbial analysis revealed that I35 had the highest CFU count at 7.67 × 10⁷ CFU/mL, with Gram staining and colony morphology indicating greater diversity and a higher abundance of electroactive Gram-negative populations at elevated temperatures. Performance improved with increased temperature; however, the power gains were more significant than variations in microbial counts, underscoring the importance of microbial composition, biofilm conductivity, and electron transfer efficiency. Despite having viable bacteria, F35 showed low output due to a less electroactive community and considerable charge transfer resistance. These findings highlight the need to enhance microbial quality, not just quantity, to improve MFC performance in extreme conditions and support the future application of thermally adapted biofilms in high-salinity MFC systems.