Sound speed, attenuation, and reflection in gassy sediments

Zheng, Guangying; Huang, Yiwang; Hua, Jian

doi:10.1121/1.4996440

Cited by 10 publications

(4 citation statements)

References 41 publications

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“…Although intense pressures can be generated as the bubbles collapse, this phenomenon is more localized and energy consuming than acoustic cavitation. Furthermore, acoustic energy may travel great distances in water depending on the frequency of the sound and subject to attenuation by suspended matter and/or bubbles [24,25]. In Padoley et al [22], hydrodynamic cavitation was induced by pumping distillery wastewater through a venturi using a positive-displacement pump rated at 1.1 kW.…”

Section: Effect Of Sound Excitation On Biogas Productionmentioning

confidence: 99%

Sound enhances wastewater degradation and improves anaerobic digester performance

et al. 2019

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Biogas production and wastewater quality from anaerobic digesters were studied to determine whether sound at sonic frequencies (< 20,000 Hz) could enhance their performance. In three trials with increasing waste loading rates, each of 100-day duration, the performance of control and sound-treated digesters was compared. Anaerobic digesters exposed to sound produced approximately 12% more biogas than did non-exposed digesters, and sound-treated digestate had significantly lower chemical oxygen demand. Sludge at the end of the 100-day digestion averaged 19% less carbon and 18% less nitrogen in sound-treated digesters as compared to sludge from untreated digesters. Although the mechanism(s) responsible for enhanced biogas production due to sound exposure are unknown, recordings of sound-treated digesters indicate that acoustically induced cavitation may play a role.

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Section: Effect Of Sound Excitation On Biogas Productionmentioning

confidence: 99%

Sound enhances wastewater degradation and improves anaerobic digester performance

et al. 2019

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“…This clearly shows that excitation of the gas saturated digestate with a low-frequency sound can cause ultrasonic emissions due to bubble harmonics at some distance from the sound source. As digesters typically develop distinct sludge and supernatant zones, this indicates that speakers could be placed within the supernatant and used to excite the greatest expanse of sludge while limiting sound attenuation due to suspended particles and bubbles [23]. Given the relatively small volume of the pilot-scale digesters, this was not considered as a problem, but in larger-scale digesters, speaker placement may be more critical.…”

Section: Digester Acousticsmentioning

confidence: 99%

In Situ Sonification of Anaerobic Digestion: Extended Evaluation of Performance in a Temperate Climate

et al. 2020

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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 summer of 2019, the sound-treated system produced 27% more biogas than the control system, and 74 times more during the winter when biogas production by the control systems essentially ceased. Afterwards, the control system produced more biogas due to depletion 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.

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“…The presence of gas bubbles in aquatic (underwater) sediment pores affects both geomechanical and geophysical properties of the sediment (Sills et al, 1991;Best et al, 2004;Lee, 2004;Zheng et al, 2017). The presence of gas bubbles in pore space considerably reduces the sound speed (Sills et al, 1991;Kumar and Madhusudhan, 2012) and increases the attenuation (Best et al, 2004), in comparison to a fully water-saturated sediment state.…”

Section: Introductionmentioning

confidence: 99%

Gas Bubble Dynamics During Methane Hydrate Formation and its Influence on Geophysical Properties of Sediment Using High-Resolution Synchrotron Imaging and Rock Physics Modeling

et al. 2022

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Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical properties. Recent studies have shown that methane gas and hydrate can coexist in gas hydrate–bearing sediments. Accurate calibration and understanding of the fundamental processes regarding such coexisting gas bubble dynamics is essential for geophysical characterization and hazard mitigation. We conducted high-resolution synchrotron imaging of methane hydrate formation from methane gas in water-saturated sand. While previous hydrate synchrotron imaging has focused on hydrate evolution, here we focus on the gas bubble dynamics. We used a novel semantic segmentation technique based on convolutional neural networks to observe bubble dynamics before and during hydrate formation. Our results show that bubbles change shape and size even before hydrate formation. Hydrate forms on the outer surface of the bubbles, leading to reduction in bubble size, connectivity of bubbles, and the development of nano-to micro-sized bubbles. Interestingly, methane gas bubble size does not monotonously decrease with hydrate formation; rather, we observe some bubbles being completely used up during hydrate formation, while bubbles originate from hydrates in other parts. This indicates the dynamic nature of gas and hydrate formation. We also used an effective medium model including gas bubble resonance effects to study how these bubble sizes affect the geophysical properties. Gas bubble resonance modeling for field or experimental data generally considers an average or equivalent bubble size. We use synchrotron imaging data to extract individual gas bubble volumes and equivalent spherical radii from the segmented images and implement this into the rock physics model. Our modeling results show that using actual bubble size distribution has a different effect on the geophysical properties compared to the using mean and median bubble size distributions. Our imaging and modeling studies show that the existence of these small gas bubbles of a specific size range, compared to a bigger bubble of equivalent volume, may give rise to significant uncertainties in the geophysical inversion of gas quantification.

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Sound speed, attenuation, and reflection in gassy sediments

Cited by 10 publications

References 41 publications

Sound enhances wastewater degradation and improves anaerobic digester performance

Sound enhances wastewater degradation and improves anaerobic digester performance

In Situ Sonification of Anaerobic Digestion: Extended Evaluation of Performance in a Temperate Climate

Gas Bubble Dynamics During Methane Hydrate Formation and its Influence on Geophysical Properties of Sediment Using High-Resolution Synchrotron Imaging and Rock Physics Modeling

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