Enhancing methanogenesis efficiency in anaerobic digestion of food waste through incremental salinity and nanobubble utilization to domesticate inoculum: Adaptability and optimal inoculation ratios

High salinity inhibits methane production in food waste (FW) anaerobic digestion (AD). This study investigated the salinity tolerance (1 %–3 %) of inoculum acclimated with air nanobubble water (Air-NBW) and evaluated methanogenic potential under 3 % salinity across varying inoculum-to-substrate (I/S) ratios (volatile solids (VS) basis). As results, the methane yield of the Air-NBW group significantly increased by 31 %, 18 %, and 16 % (p < 0.05 for all phases) relative to the control group across the three phases. Remarkably, the lag period in the Air-NBW group exhibited a notable reduction as the salinity increased, particularly at the salinity of 2 % where a significant decrease of 14 days in the lag period was observed in comparison to the control group. Additionally, the Air-NBW digester showed a non-significant increase in methane yield (228.88 ± 4.36 mL/g-VSfed, p = 0.061) at I/S = 1, while demonstrating a significant increase to 307.45 ± 3.77 mL/g-VSfed at I/S = 0.5 (p = 0.007 < 0.05) compared to the DW groups at equivalent I/S ratios. These results indicate that the using a salinity-adaptable inoculum could effectively facilitate the swift initiation and sustained stability of FW digesters.