Effect of lignin structure composition on anaerobic digestion based on lignin monomer model compounds

Abstract

Due to the complex structure formed by lignin, Lignofiber raw materials are difficult to be degraded by microorganisms, and lignin itself is also difficult to be biodegraded, which is an important factor affecting the methane production of anaerobic digestion. The proportion and quantity of three monomers (H, G, S) in the lignin structure also affect the methane production of anaerobic digestion, but there are few relevant studies. The effect of monomer concentration on methanogenesis is still unclear.Therefore, phenol, guaiacol and syringol were used as the model compounds of lignin monomers, and the effects of lignin monomer concentration on anaerobic digestion were studied by batch anaerobic digestion experiments. The results showed that low concentrations (0.02 – 0.1 g/L) of phenol and guaiacol promoted the production of biogas, while high concentrations inhibited the production of methane and delayed the production of biogas peak. When phenol concentration ≥ 3.0 g/L or guaiacol concentration ≥ 8.0 g/L, biogas production was completely inhibited. In addition, 2, 6-dimethoxyphenol had no significant effect on digestion at 0.02 – 0.2 g/L, but the delay period and total biogas production increased at 1.0 – 4.0 g/L. The inhibitory effect is mainly due to the obstruction of acid production, especially acetic acid of p-phenol and guaiacol, while 2, 6-dimethoxyphenol causes acidification. The results showed that the inhibitory effect of syringyl lignin was lower than that of guaiacyl lignin and p-hydroxyphenyl lignin. These findings highlight the complex interplay between lignin monomers and anaerobic digestion.

Graphical Abstract