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Effect of propionate toxicity on methanogen-enriched sludge, Methanobrevibacter smithii, and Methanospirillum
1Department of Civil Engineering, University of Newcastle upon Tyne, United Kingdom.
Abstract:
The effect of propionate toxicity at different pH values (6.5, 7.0, and 8.0) on methanogen-enriched sludge. Methanobrevibacter smithii, and Methanospirillum hungatii was studied. Organisms were grown in Balch medium 3 in Hungate tubes, and toxicity was characterized by a decrease in production of methane and in bacterial numbers. Propionate inhibited bacterial growth and cumulative methane production at concentrations as low as 20 mM. In the absence of propionate, the methanogen-enriched sludge and M. smithii showed better cumulative methane production at pH 6.5 and 7.0 than at pH 8.0. However, in the presence of propionate, these organisms showed better cumulative methane production at pH 8.0. M. hungatii differed in its behavior; the best values of cumulative methane production for this organism occurred at pH 7.0. Bacterial numbers reflected the microbial response to the presence of propionate. The highest counts of methanogenic bacteria were observed at pH 6.5 and 8.0. The numbers of methanogens were affected by the presence of propionate even at concentrations as low as 20 or 30 mM; at propionate concentrations above 80 mM, the methanogen count was affected by at least 2 orders of magnitude. Upon comparison of the responses of the pure cultures and the methanogen-enriched sludge to increasing propionate concentrations, it was found that the sensitivity of the pure cultures was similar to that of the methanogens in the sludge.
Insights
Propionate toxicity impacts methanogen growth and methane production. Optimal pH for methanogens shifts in the presence of propionate, with methanogen-enriched sludge and Methanobrevibacter smithii favoring pH 8.0.
Area of Science:
- Microbiology
- Environmental Science
- Biochemistry
Background:
- Methanogens are crucial for anaerobic digestion and methane production.
- Propionate is a common intermediate in anaerobic digestion, and its accumulation can inhibit methanogenesis.
- Understanding the effects of propionate toxicity and pH on methanogens is vital for optimizing biogas production.
Purpose of the Study:
- To investigate the impact of propionate toxicity on methanogen-enriched sludge, Methanobrevibacter smithii, and Methanospirillum hungatii at varying pH levels (6.5, 7.0, and 8.0).
- To characterize the inhibition of methane production and bacterial numbers by propionate.
- To determine the optimal pH conditions for methanogens under propionate stress.
Main Methods:
- Organisms were cultured in Balch medium 3 within Hungate tubes.
- Toxicity was assessed by measuring methane production and bacterial counts.
- Propionate concentrations were varied to determine inhibitory levels.
Main Results:
- Propionate inhibited bacterial growth and methane production at concentrations as low as 20 mM.
- In the absence of propionate, methanogen-enriched sludge and M. smithii performed best at pH 6.5 and 7.0.
- In the presence of propionate, these organisms showed improved methane production at pH 8.0, while M. hungatii preferred pH 7.0.
- Propionate significantly reduced methanogen counts, especially at concentrations above 80 mM.
- Pure cultures and sludge methanogens exhibited similar sensitivity to propionate.
Conclusions:
- pH significantly influences propionate toxicity in methanogens.
- Alkaline pH (8.0) can mitigate propionate inhibition for certain methanogens, which is crucial for anaerobic digestion optimization.
- Methanogen-enriched sludge and pure cultures demonstrate comparable responses to propionate toxicity, validating their use in toxicity studies.