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

Abstract

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 0.20gg-TSsubstrate−1, 80°C, 3.0h 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 243mLg-VS−1, which is 51% higher than the un-treated (161mLg-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.