Bacterial synergy and relay for thermophilic hydrogen production through dark fermentation using food waste

Background: Food waste is a significant global issue, with 1.3 billion tons generated annually, a figure expected to rise to 2.1 billion tons by 2030. Conventional disposal methods, such as landfilling and incineration, present environmental challenges, including methane emissions and pollution. Hydrogen production through dark fermentation presents a sustainable alternative, offering both waste management and renewable energy generation. This study investigates the bacterial synergy and relay mechanisms involved in thermophilic H₂ production using food waste as a substrate.

Purpose: The primary aim of this research was to analyze the metabolic pathways and dynamics of functional genes prediction during thermophilic H₂ production from food waste, focusing on the role of bacterial consortia in enhancing H₂ yields.

Methods: A continuous stirred-tank reactor (CSTR) was operated using food waste as the substrate and a thermophilic bacterial consortium as the inoculum. The study utilized genomic analysis to monitor changes in bacteriobiome composition over time and to correlate these changes with H₂ production. Volatile fatty acids (VFAs) and H₂ production rates were analyzed using gas chromatography and high-performance liquid chromatography (HPLC). The Kyoto Encyclopedia of Genes and Genomes (KEGG) database was employed to identify functional genes involved in the fermentation process.

Results: The study identified key bacterial species, including Caproiciproducens and Caproicibacter, that dominated during the later stages of H₂ production, replacing earlier dominant species such as Clostridium. These shifts in bacterial dominance were strongly correlated with sustained H₂ production rates ranging from 353 to 403 mL·L^-1·h^-1, with H₂ concentrations between 55 % and 62 % (v/v). Functional gene analysis revealed significant pathways related to polysaccharide degradation, glycolysis, and dark fermentation.

Conclusions: This study highlights the importance of bacterial synergy and relay in maintaining continuous H₂ production from food waste under thermophilic conditions. The findings provide insights into optimizing biohydrogen production processes, emphasizing the role of specific bacterial species in enhancing efficiency. These results contribute to the development of sustainable waste management strategies and renewable energy production.