Microbiome diversity of anaerobic digesters is enhanced by microaeration and low frequency sound

Authors: Loughrin, John; Parekh, Rohan; Agga, Getahun; Silva, Philip - Phil; Sistani, Karamat

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2023
Publication Date: 9/20/2023
Citation: Loughrin, J.H., Parekh, R.R., Agga, G.E., Silva, P.J., Sistani, K.R. 2023. Microbiome diversity of anaerobic digesters is enhanced by microaeration and low frequency sound. Microorganisms. 11(9), Article 2349. https://doi.org/10.3390/microorganisms11092349.
DOI: https://doi.org/10.3390/microorganisms11092349

Interpretive Summary: Biogas is a renewable source of energy produced by a complex community of microorganisms. Means of improving biogas production are needed both to improve agricultural waste treatment and provide farm income. Researchers studied how this community of microorganisms was affected by the addition of small amounts of air to a digestion of poultry litter as well as treatment with sound produced by underwater speakers. Both aeration and sound enhanced biogas production relative to no treatment while combining these treatments was not as effective as microaeration alone. Early in the experiment, microbial diversity was low with over 80% of microorganisms belonging to just three groups of bacteria. By week 23, the bacterial community was more diverse with many belonging to well-known degraders of plant material. There was also an increase in bacterial groups that produce compounds such as hydrogen and small organic acids that foster the growth of other microorganisms. Microbial diversity continued to increase, and by week 42 there was a great increase in the proportion of methanogens which are microorganisms that produce methane, the major component of biogas. No pronounced shift in the composition of the microbial community were observed due to either air or sound treatment. Rather, microbial diversity was enhanced relative to the control. It is likely that both treatments aid in waste breakdown and improve nutrient availability to promote growth and increase biogas production.

Technical Abstract: Biogas is produced by a consortium of bacteria and archaea. We studied how the microbiome of poultry litter digestate was affected by time and treatments that enhanced biogas production. The microbiome was analyzed at six, 23, and 42 weeks of incubation. Starting at week seven, the di-gesters underwent four treatments: control, microaeration with 6 mL air L-1 digestate per day, treatment with a 1000 Hz sine wave, or treatment with the sound wave and microaeration. Both microaeration and sound enhanced biogas production relative to the control while combining these treatments was not as effective as microaeration alone. At week six, over 80% of the mi-crobiome of the four digesters was composed of Actinobacteria, Proteobacteria, and Firmicutes, with less than 10% Euryarchaeota and Bacteroidetes. At week 23, the digester microbiomes were more diverse with Spirochaetes, Synergistetes, and Verrucomicrobia increasing in proportion and the abundance of Actinobacteria decreasing. At week 42, Firmicutes, Bacteroidetes, Euryarchaeota, and Actinobacteria were dominant. Other than the relative proportions of Firmicutes being in-creased and proportions of Bacteroidetes being decreased by the treatments, no systematic shifts in the biomes were observed due to treatment. Rather, microbial diversity was enhanced relative to the control. It is likely that both treatments aid in sludge breakdown and improve nutrient availability to promote growth and increase biogas production.