Biohydrogen production from food waste using a novel rotational drum reactor integrated with milli-magnetite.

Dark fermentation, regarded as a promising path for sustainable hydrogen production from food waste, is hindered by slow hydrolysis and low hydrogen yield. This study presented a novel rotational drum reactor integrated with milli-magnetite (RD-M) to enhance hydrogen production, using potato peel as feedstock. The RD-M designed to simultaneously achieve grinding and biochemical stimulation. To verify the promoting performance and elucidate the underlying mechanisms, a drum reactor with sand (RD-S) and one without additives (RD-C) were used as controls. Enhanced hydrolysis in RD-M was confirmed from a smaller dominant particle size distribution (100-500 µm), accelerated production of organic acids (e.g., acetate, butyrate), and increased volatile solids degradation (by 23.6 %) compared to RD-C. Notably, hydrogen production in RD-M increased by 97.04 %. The RD-M system induced a shift in fermentation to an acetate-butyrate pathway, associated with an enrichment of butyrate-producing Clostridium. Metagenomic analysis further revealed that milli-magnetite established an efficient electron transfer chain that improved electron utilization and hydrogen yield. Additives were shown to promote direct interspecies electron transfer by upregulating genes encoding flagella and cytochrome-c synthesis. Furthermore, intracellular electron bifurcation at pyruvate ferredoxin directed electrons into the butyrate pathway, while enhanced iron metabolism explained the fermentation shift observed in RD-M. This study highlights the combined mechanical and biochemical benefits of RD-M, offering a promising solution for sustainable biohydrogen production from solid waste.