Impact of agitation and non-agitation on microbiota and reactor performance in anaerobic digestion

Abstract

Optimizing process conditions in anaerobic digestion could enhance the utilization of organic matter for renewable energy generation. Thus, initial upset substrates with elevated volatile fatty acids were investigated under agitation and non-agitation conditions for optimal bioreactor performance. There were two continuous agitation scenarios for the liquid-state (40 and 100 rpm) with a non-agitated scenario. Similarly, a non-agitated and 40 rpm scenario for the solid-state. The result indicated that the non-agitated liquid-state reactor had the highest methane yield (193 L/kgVS) and lowest retention (51 days) despite delayed microbial adaptation. Of the prominent microbes, the relative abundance of Firmicutes and Archaea_unclassified negatively correlated with VFA at 100 rpm. Contrarily at 40 rpm, Firmicutes correlated positively with VFA, an indication that Firmicutes could withstand acid production at agitation speed ≤40 rpm suggesting that agitation associated with VFA might reduce microbial diversity in an initial upset liquid-state bioreactor. Thus, upset influent could be utilized for energy generation with a non-agitated liquid-state bioreactor.

Keywords

Agitation speed / Process parameter / Microbial diversity / Kinetic model

Authors’ contribution

AA and SR conceived and designed the research. AA conducted the experiments. AA analyzed the data. AA wrote the manuscript. SR revised the manuscript. All authors read and approved the manuscript.

Funding

This study received no external funding.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors.

Declaration of competing interest

The authors declare there is no competing financial interests/personal relationships interest.

Acknowledgement

The time and energy invested in the chemical compositional analyses facilitated by Marsha Kapphahn, Laurie Geyer, Veselina Valkov, and Yssi Entzie of the Nutrition Laboratory, Animal Science Department, North Dakota State University, Fargo, ND was highly appreciated.

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