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.
Highlights
Since the widespread adoption of concentrated animal feeding operations (CAFO) in the latter half of the twentieth century, tremendous amounts of animal manures are produced upon limited acreage so that it cannot be disposed of in an environmentally sound and efficient manner
As an alternative to ultrasonic pretreatment, we investigated whether continuous in situ treatment of digestate with sound at sonic frequencies (
We have investigated whether microaeration would enhance biogas production of poultry litter, a waste product that is normally considered to be a poor candidate for anaerobic digestion due to its high N and lignin content [15]
Summary
Since the widespread adoption of concentrated animal feeding operations (CAFO) in the latter half of the twentieth century, tremendous amounts of animal manures are produced upon limited acreage so that it cannot be disposed of in an environmentally sound and efficient manner Instead, these wastes are usually treated in facultative anaerobic lagoons, the effectiveness of which varies seasonally, and applied to fields at rates that foster the over accumulation of phosphates and other plant nutrients in soils as well as the runoff of oxygen-consuming organic matter, pathogens, and endocrine-disrupting chemical compounds to waterways [1]. Conventional wastewater treatment systems such as the activated sludge process are expensive and most often associated with municipal wastewater treatment where loading rates are comparatively low and influent solids are minimal
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