In situ sonification of anaerobic digestion: Extended evaluation of performance in a temperate climate

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

Submitted to: Energies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2020
Publication Date: 10/14/2020
Citation: Loughrin, J.H., Antle, S.W., Simmons, J.R., Sistani, K.R., Lovanh, N.C. 2020. In situ sonification of anaerobic digestion: Extended evaluation of performance in a temperate climate. Energies. 13(20). Article 5349. https://doi.org/10.3390/en13205349.
DOI: https://doi.org/10.3390/en13205349

Interpretive Summary: Increasing the efficiency of anaerobic digesters and improving sludge breakdown is vital to reducing the cost of biogas production and reducing the environmental consequences of sludge disposal. The performance of two unheated anaerobic digestion systems, one exposed to sound at <20 kHz by waterproofed speakers and one acting as a control, were compared for over a year. The digester systems were both composed of 3,000 gallon primary and 1,000 gallon secondary anaerobic tanks, 800 gallon tertiary tanks and an aerated holding tank from which the discharge was mixed with feed and circulated back to the system. Exposure of the gas saturated liquid to a low frequency sine wave induced numerous bubble harmonics up to, and presumably beyond the range of human hearing, showing that sonification of a highly gaseous liquid might be used to accomplish low power ultra-sonification of digesters at greater distances than is possible with conventional ultrasonic technology. Through the late spring of 2019 through April 2020, the sound treated system produced more biogas than the control system, especially during the winter when biogas production by the control systems essentially ceased. Afterwards, the control system produced more biogas due to exhaustion of organic matter solids in the sound treated digester. Results show that sound can be used for faster digester startup and substitute for a portion of heating requirements during cool months.

Technical Abstract: Increasing the efficiency of anaerobic digesters and improving sludge breakdown is vital to reducing the cost of biogas production and reducing the environmental consequences of sludge disposal. The performance of two unheated anaerobic digestion systems, one exposed to sound at <20 kHz by waterproofed speakers and one acting as a control, were compared for over a year. The digester systems were both composed of primary (11.4 m3) and secondary (3.8 m3) anaerobic tanks, facultative tertiary (3.0 m3) tanks and an aerobic holding tank from which effluent was mixed with feed and recirculated back to the system. Exposure of the gas saturated digestate to a low frequency sine wave induced numerous bubble harmonics up to, and presumably beyond, ultrasonic range, showing that sonification of a highly gaseous liquid might be used to accomplish low power ultrasonication of digestate at greater distances than is possible with conventional ultrasonic technology. Through the late spring of 2019 through April 2020, the sound treated system produced more biogas than the control system, especially during the winter when biogas production by the control systems essentially ceased. Afterwards, the control system produced more biogas due to exhaustion of volatile solids in the sound treated digester. Results show that sound can be used for faster digester startup and substitute for a share of heating requirements during cool months.