Enhancing anaerobic digestibility of lignin-rich submerged macrophyte using thermochemical pre-treatment

The present study investigated the effect of alkaline thermochemical pre-treatment on anaerobic digestibility of two submerged macrophyte species which have significantly different lignin content. The highest hydrolysis efficiency was achieved at NaOH loading rate of 0.20 gg-TSsubstrate-1, 80 degrees C, 3.0 h for both species. Alkaline delignification was much conspicuous in lignin-rich macrophyte (Potamogeton maackianus) as compared with lignin-poor macrophyte (Egeria densa). Ferulic acid, which is cross-linked with lignin polymer and polysaccharides, remarkably declined with increase of NaOH loading rate. It suggests that alkali removed lignin-ferulate complex from the surface of polysaccharides. The CH4 yield of pre-treated P. maackianus was 243 mLg-VS-1, which is 51% higher than the un-treated (161 mLg-VS-1). In contrast, the CH4 yield of pre-treated E. densa was 24% higher than the un-treated. These results indicated that alkaline thermochemical pre-treatment could be an effective method for anaerobic digestion of lignin-rich macrophytes. However, it was also suggested that the high NaOH addition to lignin-rich macrophyte possibly inhibit the methane recovery, due to the increase of solubilized lignin in the digestate. (C) 2015 Elsevier B.V. All rights reserved.