Microbial community adaptation influences long-chain fatty acid conversion during anaerobic codigestion of fats, oils, and grease with municipal sludge

Abstract

Codigesting fats, oils, and greases with municipal wastewater sludge can greatly improve biomethane recovery at wastewater treatment facilities. Process loading rates of fats, oils, and greases have been previously tested with little knowledge of the digester microbial community structure, and high transient fat loadings have led to long chain fatty acid (LCFA) accumulation and digester upsets. This study utilized recently-developed quantitative PCR assays for syntrophic LCFA-degrading bacteria along with 16S amplicon sequencing to relate changes in microbial community structure to LCFA accumulation during transient loading increases to an anaerobic codigester receiving waste restaurant oil and municipal wastewater sludge. The 16S rRNA gene concentration of the syntrophic β-oxidizing genus Syntrophomonas increased to ∼15% of the Bacteria community in the codigester, but stayed below 3% in the control digester that was fed only wastewater sludge. Methanosaeta and Methanospirillum were the dominant methanogenic genera enriched in the codigester, and together comprised over 80% of the Archaea community by the end of the experimental period. Constrained ordination showed that changes in the codigester Bacteria and Archaea community structures were related to measures of digester performance. Notably, the effluent LCFA concentration in the codigester was positively correlated to the specific loading rate of waste oil normalized to the Syntrophomonas 16S rRNA concentration. Specific loading rates of 0-1.5 × 10(-12) g VS oil/16S gene copies-day resulted in LCFA concentrations below 30 mg/g TS, whereas LCFA accumulated up to 104 mg/g TS at higher transient loading rates. Based on the community-dependent loading limitations found, enhanced biomethane production from high loadings of fats, oils and greases can be achieved by promoting a higher biomass of slow-growing syntrophic consortia, such as with longer digester solids retention times. This work also demonstrates the potential for controlling the loading rate of fats, oils, and greases based on the analysis of the codigester community structure, such as with quantitative PCR measurements of syntrophic LCFA-degrading bacteria abundance.

Microbial rRNA gene expression and co‐occurrence profiles associate with biokinetics and elemental composition in full‐scale anaerobic digesters

“…S3). Higher concentrations of Syntrophomonas have previously been correlated with higher degradation rates of LCFA in anaerobic digestion (Ziels et al ., , , ). Recently, 16S rRNA gene expression of Syntrophomonas was correlated with methane production from LCFA‐rich waste (Amha et al ., ).…”

Inhibition of anaerobic digestion processes: Applications of molecular tools

“…Notably, resilience was found to be an important factor in maintaining a syntrophic population exposed to disturbances in a full-scale reactor, where syntrophs rebounded following stress conditions (Werner et al, 2011). Another study also suggested reversibility of LCFA inhibition due to an increase in relative abundance of syntrophic β-oxidizing bacteria, primarily Syntrophomonas (Ziels et al, 2016). Further, the same study reported that the abundance and composition of methanogens was unaffected by addition of 100-1570 mg oleic acid g VS −1 , where 70% of the methanogens were hydrogenotrophic (Methanomicrobiales) and 30% were acetoclastic (Methanosaeta).…”

“…Although fatty acid-based inhibition is not well understood, researchers have identified several likely mechanisms of inhibition: disruption of the electron transport chain and oxidative phosphorylation, interference with cellular energy production, direct lysis of bacterial cells, and decreased cell permeability (Desbois and Smith, 2010;Pereira et al, 2005). However, some studies have suggested that LCFA inhibition is reversible Pereira et al, 2005;Ziels et al, 2016). For example, a study involving cattle manure digestion with the addition of sodium oleate to simulate high LCFAs reported that the perturbation observed was reversible .…”

Feasibility and potential of separate anaerobic digestion of municipal sewage sludge fractions

“…Dewatering ability of the stabilised SS proceeded with a fluctuating pattern throughout the study with a limited improvement at the highest VLRs (0.44 and 0.57 kg VS/(m 3 •d)) indicating that lower HRT, thus, lower destruction of SS, may require a lower chemical/polymer consumption at the decanter unit than lower VLRs/higher HRT. High oil and grease content is known to affect stabilised sludge dewaterability and beneficial usage in a negative direction (Ziels et al, 2016). Reduction in filtering time in stabilised PS to lower levels than stabilised SS was correlated to efficient removal of oil and grease.…”