Anaerobic Digestion: Strategies for Increasing Biogas Production Performance in Halophilic Conditions

Abstract

Anaerobic digestion (AD) is a common technology leading sustainable waste management and renewable energy recovery. However, high salinity in feedstocks significantly hinders its efficiency. This study evaluates strategies to optimize methanogenesis under halophilic conditions, focusing on inoculum selection and acclimation strategy. A methanogen database analysis revealed that while non-halophiles dominate mesophilic species, moderate halophiles exhibit higher growth rates (median: 0.12 h⁻¹ vs. 0.03 h⁻¹ for non-halophiles) and salt tolerance, positioning them as key species for a feasible saline methanogenesis. More importantly, hydrogenotrophic methanogens, prevalent in mesophilic systems, is a critical metabolic pathway for methane production. Kinetic experiments using solar saltern sediments and landfill leachate inocula under 0.3–1.1 M salt stress (Na⁺/K⁺/NH₄⁺ = 76/16/8 mol%) demonstrated different results: solar saltern sediments produced methane using different substrates at 0.3 M with low rates (acetate: 2.56 NmL/gVS/d; propionate: 3.64 NmL/gVS/d) and prolonged lag phases (>70 days), while landfill leachate achieved higher methane production at 0.3 M (qCH₄ₘₐₓ = 82.86 NmL/gVS/d) after 2 days of lag phase but was inhibited severely and had longer lag phase (35 days) at 0.5 M (qCH₄ₘₐₓ = 6.08 NmL/gVS/d). Acclimation of solar saltern sediments to 0.7 M salinity enabled production (specific biogas yield: 19.62 NmL/gVS by day 85), whereas non-adapted industrial digestate and mixed inocula have longer lag phases and limited methane output. These results highlight the critical role of inoculum origin and acclimation in overcoming osmotic stress, which provides essential insights for designing halophilic AD systems. Microbial adaptation protocols and good inoculum selection are crucial for enhancing biogas recovery from saline feedstocks.