Abstract
Sound has the potential to increase biogas yields and enhance wastewater degradation in anaerobic digesters. 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. 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 and had more cavitational events than those of the control digester, which we ascribe to enhanced microbial growth and the resulting accelerated sludge breakdown. Acoustic cavitation, vibrational energy imparted to wastewater and sludge, and mixing due to a release of bubbles from the sludge may all act in concert to accelerate wastewater degradation and boost biogas production.
Highlights
Anaerobic digestion, in simplified form, is the process wherein organic matter is broken down in an oxygen-free environment by the combined processes of fermentation and methanogenesis to produce biogas, a mixture of carbon dioxide and methane, in addition to trace gases such as hydrogen sulfide and ammonia [1]
It was planned to compare the performance of speakers placed facing towards the bottom of the tank to those placed facing transversely at the bottom of the tank to determine if this would affect relative biogas production
We realized that this was not possible, since the system would exhibit hysteresis, and the amount of biogas produced would partially depend on the degree to which the previous sound treatment had affected sludge breakdown
Summary
In simplified form, is the process wherein organic matter is broken down in an oxygen-free environment by the combined processes of fermentation and methanogenesis to produce biogas, a mixture of carbon dioxide and methane, in addition to trace gases such as hydrogen sulfide and ammonia [1]. Ultrasonification (>20 kHz) of waste has been used as a pretreatment to help disintegrate sludge particles, thereby enhancing wastewater degradation and biogas production [6,12,13] This is a form of noninertial cavitation, wherein a bubble oscillates in the presence of an acoustic field. As a pretreatment, this differed from our research, wherein sound at sonic frequencies (
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