In situ acoustic treatment of anaerobic digesters to improve biogas yields

Authors: Loughrin, John; Antle, Stacy; Sistani, Karamat; Lovanh, Nanh

Submitted to: Springer Nature Applied Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2020
Publication Date: 2/8/2020
Citation: Loughrin, J.H., Antle, S.W., Sistani, K.R., Lovanh, N.C. 2020. In situ acoustic treatment of anaerobic digesters to improve biogas yields. Springer Nature Applied Sciences. 7(2):11. https://doi.org/10.3390/environments7020011.
DOI: https://doi.org/10.3390/environments7020011

Interpretive Summary: Biogas, a mixture of predominantly methane and carbon dioxide, is a valuable renewable energy source generated by the anaerobic (in the absence of oxygen) decomposition of animal manure and other agricultural wastes. Biogas production is limited, however, by slow rates of gas production. Sound has the potential to increase biogas yields from anaerobic digesters by enhancing sludge degradation. To assess this potential, two digestion systems were operated with one exposed to sound at audible frequencies and with one acting as a control. A variety of sounds were used including broadband noise and orchestral compositions. We found that weekly biogas production from sound-treated digesters was 18,900 liters, more than twice that of the control digester. Background recordings from the sound-treated digester were louder than those of the control digester which we ascribe to sludge breakdown and enhanced microbial growth. Sound treatment of wastewater may serve to exploit potential energy in the form of bubbles in the highly gaseous, supersaturated environment of anaerobic digesters and enhance biogas production as well as wastewater treatment.

Technical Abstract: Sound has the potential to increase biogas yields from anaerobic digesters by enhancing sludge degradation. To assess this potential, two pilot-scale digestion systems were operated with one exposed to sound at less than 10-kHz and with one acting as a control. Sounds used were sine waves, broadband noise and orchestral compositions. We found that weekly biogas production from sound-treated digesters was 18,900-L, more than twice that of the control digester. The sound-treated digesters were primarily exposed to orchestral compositions because this made cavitational events easier to identify, and because harmonic and amplitude shifts in music seem to induce more cavitation. Background recordings from the sound-treated digester were louder than those of the control digester which we ascribe to sludge breakdown and enhanced microbial growth. Acoustically-induced cavitation may serve to exploit potential energy in the form of bubbles in the highly gaseous, supersaturated digestate.