Biochemical methane potential assays and anaerobic digester bioaugmentation using freeze dried biomass†
In this study, freeze dried methanogenic biomass (FDMB) was used as inoculum in place of conventional, non-dried biomass for biochemical methane potential (BMP) assays and as a bioaugment to improve upset digester recovery. Methanogenic biomass was freeze dried and stored in an air atmosphere. Significant methanogenic activity was preserved in FDMB even with drying and storage in air; specific methanogenic activity (SMA) values were 65 ± 4.5% and 42 ± 10.4% for hydrogen:carbon dioxide (H2:CO2) and acetate, respectively, compared to non-dried biomass. There was no significant difference in BMP results for the four substrates tested (glucose, non-fat dry milk, thin stillage and dog food) when using FDMB and non-dried biomass as inocula. However, BMP assays using FDMB inocula took longer to complete. Methane (CH4) production from digesters exposed to a model toxicant (oxygen [O2]) recovered faster when bioaugmented with FDMB compared to digesters that received autoclaved biomass or no bioaugmentation. Methanogen communities in all digesters before toxicant exposure and bioaugmentation were similar. However, bioaugmented and non-augmented digester communities were significantly different during the recovery phase after toxicant exposure. Sequences similar to Methanospirillum were related to improved performance of the FDMB bioaugmented digesters. FDMB could be developed as a standard inoculum for BMP analyses and to bioaugment anaerobic digesters for improved performance. These results may encourage developing customized, dried methanogenic biomass for specific anaerobic biotechnology applications.