Bioaugmentation of Anaerobic Digesters Can Increase CH4 Production and Cod Removal
Published as part of the proceedings of the conference, Central States Water Environment Association, 2012 Annual Meeting, 2012. Permalink.
Bioaugmentation is the practice of adding specific microbes to a system to achieve process improvement. It has typically been used for aerobic processes including nitrification or bioremediation of specific pollutants. Bioaugmentation of anaerobic digesters has not been thoroughly studied, and full-scale applications are rare or non-existent. However, limited prior research on anaerobic bioaugmentation has shown beneficial results such as faster digester startup and recovery after upset (Schauer-Gimenez, 2010; Tale et al., 2011). Although the approach appears promising, these studies were limited to digesters under transient, upset conditions—pointing to the need to investigate bioaugmentation for steady-state anaerobic digesters under conventional operating conditions. It would also be valuable to determine the reason(s) why some digesters have responded positively to bioaugmentation with a given culture, whereas others have not (Schauer-Gimenez et al., 2010). In the work to be described, two sets of anaerobic digesters were initially started using different inocula from municipal anaerobic systems in Des Moines, IA and Philadelphia, PA. (Chosen for their unique microbial structures and activities). Some digesters in each set were bioaugmented, while others were not, and differences in biogas production and COD removal were compared. The bioaugmented digesters received a unique enrichment culture developed to increase CH4 production as described elsewhere (Schauer-Gimenez et al., 2010; Tale et al., 2011).
Each set contained digesters that were bioaugmented with live culture (Bioaugmented), digesters augmented with autoclaved culture (Inactive), and digesters that were not augmented or bioaugmented (Control). Each condition was run in triplicate. All digesters were 160-mL serum bottles with a 50-mL working volume operated at a 10-day hydraulic residence time (HRT) and fed a synthetic industrial waste (non fat-dry milk) at an organic loading rate (OLR) of 4 g COD/LR-day.
Bioaugmentation of digesters seeded with Des Moines biomass resulted in significantly higher average CH4 production rate (p value < 0.05, n = 120) compared to non-bioaugmented digesters; CH4 production was 13 and 11% greater than Control and Inactive digesters (Table 1, Figure 1). In contrast, bioaugmentation of digesters seeded with Philadelphia biomass did not result in increased CH4 production. (Table 1, Figure 2). A similar influence of bioaugmentation was observed for effluent SCOD concentration; with Des Moines systems benefiting from bioaugmentation, and Philadelphia systems exhibiting no improvement (Table 1 and Figure 3, 4). The difference in outcomes observed between the Des Moines and Philadelphia sets is putatively due to the different starting inocula employed. This is similar to the findings of Schauer- Gimenez et al. (2010) who observed that success or failure of bioaugmentation to speed recovery of anaerobic digesters after transient exposure to a toxicant depended on the initial digester microbial community. We are currently using molecular tools to describe and compare the microbial community structures of different digesters to investigate the relationship between microbial community structure and the probability of a given digester benefiting from bioaugmentation.