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>0.3), whereas the tree structures of non-bioaugmented and undisturbed control digesters differed significantly (pMethanospirillum hungatei may have caused better performance of bioaugmented digesters.