Bioaugmentation For Recovery of Anaerobic Digesters Subjected to Organic Overload

Anaerobic digester upset due to organic overload is common and methods to reduce recovery time would be beneficial. One potential method is bioaugmentation, the addition of an external culture for performance improvement. Methanogenic community structure differs from digester to digester and there may exist a relation between specific methanogenic activity (SMA) and microbial community composition. The research presented herein tested whether there is a relationship between SMA and community structure. Also, the effectiveness of bioaugmentation was tested by hypothesizing that bioaugmenting with a methanogenic, propionate-degrading culture acclimated to small oxygen doses will help rapid recovery of organically overloaded digesters. Fourteen different anaerobic cultures were tested for SMA and microbial community using the mcrA gene and DGGE to establish a relationship between SMA and community structure. The culture with the highest SMA was enriched by feeding 0.17g propionate/L-day and different oxygen doses. The enrichment cultures were used to bioaugment organically overloaded anaerobic digesters. Microbial communities present in bioaugmented, non-bioaugmented and undisturbed control digesters as well as the bioaugmentation culture were analyzed using 16S rDNA. A statistically significant relationship between SMA and community structure could not be established, highlighting the difficulty in establishing activity/community structure relationships. However, the results indicated that there was a relation between SMA and methanogenic community compositions studied. Enriching a culture for 25mgO2/L-day increased its SMA by 29.7%, but higher oxygen doses yielded lower SMA values. Bioaugmentation with this enrichment culture reduced the time required for upset digester effluent to decrease below 1000mgSCOD/L by 114 days (11.4 SRTs) and the time required to reach 25mLCH4/day by 37 days (3.7 SRTs) respectively. Bioaugmented digesters consistently produced lower effluent SCOD and more methane than non-bioaugmented digesters. Bioaugmentation is a promising approach for speeding up recovery of organically overloaded digesters. Bacterial and archaeal communities of the bioaugmented and undisturbed control digesters had similar phylogenetic tree structures (p\u3e0.3), whereas the tree structures of non-bioaugmented and undisturbed control digesters differed significantly (pMethanospirillum hungatei may have caused better performance of bioaugmented digesters

Bioaugmentation of Overloaded Anaerobic Digesters Restores Function and Archaeal Community

Adding beneficial microorganisms to anaerobic digesters for improved performance (i.e. bioaugmentation) has been shown to decrease recovery time after organic overload or toxicity upset. Compared to strictly anaerobic cultures, adding aerotolerant methanogenic cultures may be more practical since they exhibit higher methanogenic activity and can be easily dried and stored in ambient air for future shipping and use. In this study, anaerobic digesters were bioaugmented with both anaerobic and aerated, methanogenic propionate enrichment cultures after a transient organic overload. Digesters bioaugmented with anaerobic and moderately aerated cultures recovered 25 and 100 days before non-bioaugmented digesters, respectively. Increased methane production due to bioaugmentation continued a long time, with 50–120% increases 6 to 12 SRTs (60–120 days) after overload. In contrast to the anaerobic enrichment, the aerated enrichments were more effective as bioaugmentation cultures, resulting in faster recovery of upset digester methane and COD removal rates. Sixty days after overload, the bioaugmented digester archaeal community was not shifted, but was restored to one similar to the pre-overload community. In contrast, non-bioaugmented digester archaeal communities before and after overload were significantly different. Organisms most similar to Methanospirillum hungatei had higher relative abundance in well-operating, undisturbed and bioaugmented digesters, whereas organisms similar to Methanolinea tarda were more abundant in upset, non-bioaugmented digesters. Bioaugmentation is a beneficial approach to increase digester recovery rate after transient organic overload events. Moderately aerated, methanogenic propionate enrichment cultures were more beneficial augments than a strictly anaerobic enrichment

\u3cem\u3emcrA\u3c/em\u3e Gene Abundance Correlates with Hydrogenotrophic Methane Production Rates in Full-scale Anaerobic Waste Treatment Systems

Anaerobic treatment is a sustainable and economical technology for waste stabilization and production of methane as a renewable energy. However, the process is under-utilized due to operational challenges. Organic overload or toxicants can stress the microbial community that performs waste degradation, resulting in system failure. In addition, not all methanogenic microbial communities are equally capable of consistent, maximum biogas production. Opinion varies as to which parameters should be used to monitor the fitness of digester biomass. No standard molecular tools are currently in use to monitor and compare full-scale operations. It was hypothesized that determining the number of gene copies of mcrA, a methanogen-specific gene, would positively correlate with specific methanogenic activity (SMA) rates from biomass samples from six full-scale anaerobic digester systems. Positive correlations were observed between mcrA gene copy numbers and methane production rates against H2 : CO2 and propionate (R2 = 0·67–0·70, P \u3c 0·05) but not acetate (R2 = 0·49, P \u3e 0·05). Results from this study indicate that mcrA gene targeted qPCR can be used as an alternate tool to monitor and compare certain methanogen communities in anaerobic digesters