Community dynamics and significance of anaerobic protozoa during biomethanation of lignocellulosic waste

• Community structure and dynamics of anaerobic protozoa in an anaerobic digester is determined.
• Importance of protozoa at different stages of anaerobic digestion is shown.
• Hydrolytic enzyme activity can be correlated with the anaerobic protozoa count.
• Demonstrates a high correlation between specific enzymes and the different protozoa present.

The diversity and community dynamics of anaerobic protozoa and their functional role during anaerobic digestion of a typical lignocellulose biomass in a lab scale leach bed coupled UASB reactor is reported in this study. The functional role played by different protozoa during various stages of methanogenesis was analyzed through linear regression analysis of individual protozoon counts with major hydrolytic enzyme activities, volatile fatty acid levels and biogas production. The protozoa community in the digester was represented by ciliates (Metopus, Cyclidium and Colpoda) and flagellates (Rhyncomonas, Menoidium and Bodo). Regression analysis revealed the relationship between total protozoa counts with the activity of cellulase (R2 = 0.71) pectinase (R2 = 0.50) amylase (R2 = 0.53) and xylanase (R2 = 0.34), total volatile fatty acid levels (R2 = 0.86) and biogas production (R2 = 0.78) in the digester. Moreover, it was found that both volatile fatty acid and biogas production is correlated with ciliate and flagellate populations. This study underlines the importance of both ciliates and flagellates in the anaerobic digestion process and, more specifically, the contribution by individual protozoa on hydrolysis, which is the rate limiting stage in anaerobic digestion.