Harnessing methylotrophic methanogenesis to overcome salinity inhibition and sulfide production in anaerobic digestion.

Saline biomass represents an emerging feedstock for anaerobic digestion (AD), yet methane production is often limited by salinity and competition from sulfate-reducing microorganisms (SRM), leading to hydrogen sulfide formation. Unlike conventional methanogenesis pathway, methylotrophic pathway naturally thrives in saline environments by metabolizing methylated compounds without SRM interference nor saline inhibition. This study compared trimethylamine (TmaCl) and microcrystalline cellulose (MCC) as substrates, with or without molybdate (SRM inhibitor), at 0 and 25 g sea salt/L. Methane yields and kinetics from the methylotrophic pathway remained stable under salinity and equaled the MCC control at 0 g/L. In contrast, MCC showed a fivefold decrease in methane production and a threefold increase in lag time at high salinity. Moreover, methylotrophic conditions reduced H2S emissions by over 30-fold. These findings demonstrate the resilience of methylotrophic methanogenesis in saline environments, offering a promising strategy for efficient valorization of marine and saline biomasses in AD.