Complexity of acclimatization substrate affects anaerobic digester microbial community response to organic load shocks

doi:10.1016/j.envres.2022.114722

Environmental Research

Volume 216, Part 3, 1 January 2023, 114722

https://doi.org/10.1016/j.envres.2022.114722 Get rights and content

Highlights

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Microbiome response to shock load varies with acclimatization substrate complexity.
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Complex substrate-acclimatized inoculum sustains CH₄ yield even at high load.
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Alpha-diversity is stable despite shock load in complex substrate-acclimatized AD.
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Microbiome acclimatized with complex substrate shifts to more functional groups.

Abstract

This study elucidated the changes in the short-term response to organic load shocks of the anaerobic digestion (AD) microbiome acclimatized to a simple substrate and a complex substrate. Batch vial reactors were inoculated with AD sludge acclimatized to either a simple (starch and hipolypeptone) or a complex (dog food and starch) substrate, both with carbon-to-nitrogen ratio of 25. Organic loads in the form of an easily degradable substrate mix (starch and hipolypeptone) with concentrations varying from 0 to 5 g VS/L were applied to the reactors. Runs utilizing the inoculum acclimatized to a complex substrate sustained its methane productivity despite the high organic load shocks which the inoculum acclimatized to a simple substrate was unable to handle efficiently. The alpha-diversity of the microbiome decreased with increase in organic load for inoculum acclimatized with a simple substrate but was unaffected for the case of the inoculum acclimatized with a complex substrate. LactobacillalesandCloacimonadales were inferred to be major players in starch degradation pathways for the inoculum acclimatized using a simple substrate as predicted by the bioinformatics package PICRUSt2. However, acclimatizing using a complex substrate did not support their growth and were replaced by Coriobacteriales which provided higher flexibility in terms of the predicted regulated metabolic functions. The predicted functional regulation of Synergistales and Syntrophales increased with acclimatization using a complex substrate which also showed increase in the flexibility of the microbiome towards handling organic load shocks. Acetoclastic pathway was upregulated with increase in organic load regardless of the acclimatization substrate while the hydrogenotrophic pathway was downregulated. Overall, acclimatization using a complex substrate increased the robustness and flexibility of the microbiome towards organic load shocks.

Graphical abstract

Section snippets

Funding source

The present study was partially supported by JSPS KAKENHI Grant Number JP21K17906.

Anaerobic digestion sludge acclimatization

The anaerobic digester sludge that was used to start the acclimatization digesters was collected from a mesophilic (37 °C) anaerobic digester operating at the Hokubu Sludge Treatment Center located in Yokohama, Kanagawa Prefecture, Japan. The anaerobic digester sludge was acclimatized in two (2) 36-L custom-made reactors (24-L total sludge volume for each reactor). The acclimatization of the first reactor (Inoculum A) using soluble starch and hipolypeptone at 1 g VS/L/d was discussed in our

Effect of acclimatization substrate complexity on digester efficiency

Methane yields from each organic load condition were calculated to quantify the conversion efficiency of the substrate to methane (Fig. 1c and d). The methane production (Fig. 1a and b) from the 0 g VS/L OL run was subtracted from the methane production of the rest of the experimental runs. This was done to exclude the amount of methane that was produced from the conversion of the organic matter already present in the inoculum. The results utilizing Inoculum A have been discussed in detail in

Conclusions

The response of the AD microbiome to OL shocks differed depending on the complexity of the sludge acclimatization substrate. Microbial diversity decreased with higher load for sludge acclimatized to a simple substrate. Correspondingly, methane yield decreased. Microbial diversity remained stable despite high loads for sludge acclimatized with complex substrate, in which, the methane yield remained the same across varying OL. AD sludge acclimatized to a complex substrate has higher resilience

Credit author statement

Jericho Victor Mercado: Conceptualization, Methodology, Investigation, Visualization, Writing – original draft. Mitsuhiko Koyama: Conceptualization, Methodology, Writing – review & editing, Funding acquisition. Kiyohiko Nakasaki: Conceptualization, Writing – review & editing, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The present study was partially supported by JSPS KAKENHI Grant Number JP21K17906. We are also grateful to the Hokubu Sludge Treatment Center located in Yokohama, Kanagawa Prefecture, Japan, for providing the anaerobic digester sludge used as seed sludge for our study.

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View full text

Complexity of acclimatization substrate affects anaerobic digester microbial community response to organic load shocks

Highlights

Abstract

Graphical abstract

Section snippets

Funding source

Anaerobic digestion sludge acclimatization

Effect of acclimatization substrate complexity on digester efficiency

Conclusions

Credit author statement

Declaration of competing interest

Acknowledgements

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