Methanogen community structure-activity relationship and bioaugmentation of overloaded anaerobic digesters

Accumulation of acids in anaerobic digesters after organic overload can inhibit or stop CH4 production. Therefore, methods to reduce acid concentrations would be helpful. One potential method to improve recovery involves bioaugmentation, addition of specific microorganisms to improve performance. In this study, transiently overloaded digesters were bioaugmented with a propionate-degrading enrichment culture in an effort to decrease recovery time. Biomass samples from 14 different, full-scale anaerobic digesters were screened for specific methanogenic activity (SMA) against propionate; the microbial communities were also compared. SMA values spanned two orders of magnitude. Principal component analysis of denaturing gradient gel electrophoresis (DGGE) banding patterns for a functional gene (mcrA) suggested an underlying community structure-activity relationship; the presence of hydrogenotrophic methanogens closely related to Methanospirillum hungatei and Methanobacterium beijingense was associated with high propionate SMA values. The biomass sample demonstrating the highest SMA was enriched for propionate degrading activity and then used to bioaugment overloaded digesters. Bioaugmented digesters recovered more rapidly following the organic overload, requiring approximately 25 days (2.5 solids retention times (SRTs)) less to recover compared to non-bioaugmented digesters. Benefits of bioaugmentation continued for more than 12 SRTs after organic overload. Bioaugmentation is a promising approach to decrease recovery time after organic overload.

(a) Decrease in effluent SCOD concentration from bioaugmented digesters compared to non-bioaugmented digesters. (b) Increase in CH4 production rate from bioaugmented digesters compared to non-bioaugmented digesters. Error bars represent standard error among three replicates.Figure optionsDownload high-quality image (76 K)Download as PowerPoint slideHighlights
► Biomass activity from different anaerobic reactors varies; seed should be chosen carefully.
► DGGE banding pattern and SMA demonstrate a relationship between community structure and activity.
► Quantitative structure-activity relationships may be developed to improve biotechnology.
► Bioaugmentation is a promising approach to improve anaerobic digester operations.