Evaluation of microaeration and sound to increase biogas production from poultry litter

Authors: Loughrin, John; Antle, Stacy; Bryant, Michael; Berry, Zachary; Lovanh, Nanh

Submitted to: Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2020
Publication Date: 8/16/2020
Citation: Loughrin, J.H., Antle, S.W., Bryant, M.D., Berry, Z.P., Lovanh, N.C. 2020. Evaluation of microaeration and sound to increase biogas production from poultry litter. Environments. 7(8). Article 62. https://doi.org/10.3390/environments7080062.
DOI: https://doi.org/10.3390/environments7080062

Interpretive Summary: Biogas is a green fuel that can be produced by the digestion of agricultural wastes in the absence of oxygen. Much of this waste, however, is resistant to breakdown in strictly air-free (anaerobic) conditions. Microaeration, where small amounts of air are introduced into otherwise anaerobic digesters, has been shown to enhance biogas production. This occurs by fostering the growth of bacteria tolerant to small levels of oxygen and the production of enzymes that enhance the degradation of polymers such as cellulose. The treatment of anaerobic digestate with sound at sonic frequencies (<20 kHz) has also been shown to improve biogas production. Microaeration at a rate of 800 mL per day, treatment with a 1000 Hz sine wave, and combined microaeration/sound were compared to a control digester for the production of biogas and their effect on wastewater quality. Poultry litter from a facility using wood chips as bedding was used as feed. The initial feeding rate was 400 g per week, and this was slowly increased to a final rate of 2400 g per week. Compared to the control, sound treatment, aeration, and combined sound/aeration produced 17%, 32%, and 28% more biogas. The aeration alone treatment may have been more effective than combined aeration/sound due to the sound interfering with retention of aeration in the digesters or the formation of free radicals during bubble collapse. Digesters treated with sound had the highest concentrations of suspended solids likely due to suspension of fine particles by bubbles.

Technical Abstract: Microaeration, wherein small amounts of air are introduced into otherwise anaerobic digesters, has been shown to enhance biogas production. This occurs by fostering the growth of facultatively aerobic bacteria and production of enzymes that enhance the degradation of complex polymers such as cellulose. The treatment of anaerobic digestate with sound at sonic frequencies (<20 kHz) has also been shown to improve biogas production. Microaeration at a rate of 800 mL per day, treatment with a 1000 Hz sine wave, and combined microaeration/sound were compared to a control digester for the production of biogas and their effect on wastewater quality. Poultry litter from a facility using wood chips as bedding was used as feed. The initial feeding rate was 400 g per week, and this was slowly increased to a final rate of 2400 g per week. Compared to the control, sound treatment, aeration, and combined sound/aeration produced 17%, 32%, and 28% more biogas. The aeration alone treatment may have been more effective than combined aeration/sound due to the sound interfering with retention of aeration or the formation of free radicals during cavitation. Digesters treated with sound had the highest concentrations of suspended solids likely due to cavitation occurring within the sludge and the resulting suspension of fine particles by bubbles.