Thermophilic Microbial Community Succession and Biofilm Development in a Microbial Electrolysis Cell Fed with Fermented Sugarcane Vinasse

Thermophilic microbial electrolysis cells (MECs) may couple wastewater valorization with hydrogen production, but the microbial dynamics influencing their performance remain poorly understood. This study investigated microbial succession and biofilm development in a single-chamber MEC operated for 132 days at 55 °C with fermented sugarcane vinasse under 0.8, 0.9, and 1.1 V. Hydrogen production and microbial colonization were evaluated by gas analysis, scanning electron microscopy, and 16S rRNA gene amplicon sequencing of suspended and electrode-associated biomass. At 0.8 V, hydrogen accounted for 94.7% of the gas phase with a surface area-normalized H2 production rate of 30.4 L H2 m−2 d−1. During operation at 1.1 V, these parameters reached 96% and 55.4 L H2 m−2 d−1. Microscopy confirmed colonization of the carbon-felt anode at the end of operation. The community underwent marked succession: Akkermansia and Pseudomonas were transiently enriched, Caldanaerobius dominated at 0.8 V, and Moorella predominated at the final stage, representing 41.4% of the suspended and 44.9% of the electrode-associated communities. The relative abundance of Thermoanaerobacterium was higher in the electrode-associated community than in the suspended biomass (18.4% vs. 8.1%). These results demonstrate that long-term thermophilic operation selected a specialized consortium comprising fermentative, acetogenic, and potentially electrode-interacting populations while supporting high-rate hydrogen production from fermented vinasse.