Analysis of Methanogen Communities in Anaerobic Membrane Bioreactors and Conventional Anaerobic Digester Systems

Abstract

Aims: Methanogenesis is the terminal step in anaerobic digestion and is often rate-limiting and highly sensitive to environmental changes. The performance of engineered anaerobic digesters depends on methanogenesis, which is often measured indirectly through methane production and COD removal. Quantitative real-time PCR (qPCR) is a culture-independent technique that can be used to quantify populations of methanogenic archaea in anaerobic systems to provide insight into system performance and community dynamics. The aims of this paper is to use a SYBR Green-based qPCR method to quantify methanogenic archaea in a variety of anaerobic digesters as a prerequisite for long-term monitoring. Methodology: In this study, genomic DNA was extracted from mixed liquor samples from five anaerobic digesters using MO BIO Powersoil DNA Isolation kits. Primers targeted the 16S rRNA gene of different methanogens at the order- and family-level for qPCR using SYBR Green. Comparisons were made between methanogen communities from different bioreactor conditions. Results: Quantification of methanogens showed hydrogenotrophic dominance (Methanobacteriales and Methanomicrobiales) in all bioreactors treating complex feed despite the general assumption that 70% of methane is produced by acetotrophic methanogens. Furthermore, the acetotrophic dominance found in the acetic acid-fed bioreactor showed an anticipated shift in dominance from Methanosarcinaceae to Methanosaetacea when acetate concentrations decreased. Conclusions: This study illustrated that qPCR using SYBR Green can be used to quantify the distribution of methanogens in anaerobic bioreactors at the order and family level. Methanogen populations for these bioreactors were presented as well as recommendations for future implementation.