Adaptive halotolerant communities for enhanced biohydrogen production from high-salt food waste under thermophilic conditions

Food waste (FW) is a valuable but challenging substrate for sustainable hydrogen production, as its high salinity often suppresses microbial activity and process efficiency. This study examined the adaptive responses of thermophilic microbial consortia enriched under gradually increasing NaCl concentrations (1.0–3.5%) to reveal conditions that balance productivity and resilience. The consortium enriched under moderate salinity achieved the highest hydrogen yield (130.1 ± 7.3 mL·g-VS−1) with rapid onset of production, whereas the high-salinity consortium exhibited the highest hydrogen production rate (9.43 ± 1.35 mL·g-VS−1·h−1) but a lower overall yield. Metagenomic analysis revealed salinity-driven microbial succession from Thermocaproicibacter melissae to halotolerant species such as Clostridium thermopalmarium and Heyndrickxia coagulans. Functional predictions indicated shifts in carbohydrate degradation and the enrichment of salinity-tolerance genes, reflecting strategies that sustain hydrogen production under osmotic stress. These findings highlight the importance of adaptive enrichment in achieving a balance between hydrogen productivity and microbial viability under saline conditions. Rather than pointing to a single optimum, the results provide ecological and engineering insights for designing robust waste-to-energy systems capable of valorizing high-salt FW. Such systems can advance renewable energy generation, resource recovery, and environmental sustainability.