Lignin is one of the most substantial obstacles in the evaluation of lignocellulosic compounds. Although there are numerous approaches for the enhancement of lignin digestion in the literature, there has yet to be an optimized system to date. In this study, samples taken from Igneada floodplain forests were enriched anaerobically at 25 °C and 37 °C, with alkali lignin as the sole carbon source. The activity of the anaerobic lignin-degrading microbial consortium was detected more efficiently at 37 °C, where biogas production exceeded 3.5 mLgas/mLmedium. It was observed that the microbial community initially dominated by Proteobacteria (around 60%) changed completely after enrichment and was led by members of the Firmicutes phylum (up to 90%). The dominant species (Sporomusa termitida, Desulfitobacterium hafniense, Citrobacter freundii, Citrobacter portucalensis, Alkalibacter rhizosphaerae, and Gudongella oleilytica) occupying more than 50% in the final enrichment culture were only around 2% in the raw samples. Therefore, this study, one of the few in which enriched environmental samples were sequenced using MinION, demonstrated that longoses are exceptional reservoirs for lignin-digesting anaerobic microorganisms.