Evaluation of Microaeration and Sound to Increase Biogas Production from Poultry Litter

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 day−1, 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 week−1, and this was slowly increased to a final rate of 2400 g week−1. 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.

Microbiome Diversity of Anaerobic Digesters Is Enhanced by Microaeration and Low Frequency Sound

“…The digesters have been previously described [ 20 ]. Briefly, they were constructed from 208 L polyethylene tanks (US Plastic Inc., Lima, OH, USA).…”

“…The cap of each tank was modified to accept connections for gas sampling and gas volume measurement as described. Water quality, gas production, and gas quality measurements were also performed as described [ 20 , 21 ].…”

“…Sludge degradation was also substantially higher in sound-treated digesters. Later, we investigated coupling low frequency sound with microaeration to enhance biogas gas from poultry litter which used wood chips as the base material [ 20 ]. We were able to demonstrate that in situ sonification of anaerobic digestate as opposed to ultrasonic pretreatment also served to accelerate biogas production and reduce wastewater strength.…”

“…We were able to demonstrate that in situ sonification of anaerobic digestate as opposed to ultrasonic pretreatment also served to accelerate biogas production and reduce wastewater strength. In a prior study determining optimal aeration rates [ 21 ], aeration at 800 mL d −1 (6.0 mL L −1 digestate) improved biogas production at 73% compared to a strictly anaerobic digester, while in the latter study [ 20 ], aeration at 800 mL d −1 improved biogas production by 32% compared to the anaerobic control and sound treatment improved biogas production by 17%. Combined aeration and sound improved biogas production by 28% compared to the control.…”

High-Solid Anaerobic Digestion: Reviewing Strategies for Increasing Reactor Performance

“…Other techniques, such as micro-aeration, wherein small amounts of air are introduced into an anaerobic digester, have been shown to enhance biogas production. This occurs by fostering the growth of facultative aerobic bacteria and enhancing the production of enzymes that participate in the degradation of complex polymers such as cellulose [172,173]. Therefore, combining these different operating methodologies may provide a suitable means of reducing hydrolysis limitations and the accumulation of toxic intermediaries.…”