Aeration to improve biogas production by recalcitrant feedstock

Authors: Loughrin, John; Lovanh, Nanh

Submitted to: Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2019
Publication Date: 4/11/2019
Citation: Loughrin, J.H., Lovanh, N.C. 2019. Aeration to improve biogas production by recalcitrant feedstock. Environments. 6(4):44. https://doi.org/10.3390/environments6040044.
DOI: https://doi.org/10.3390/environments6040044

Interpretive Summary: Animal wastes made be digested in the absence of oxygen to produce a form of natural gas called biofuel. Rather than digesting this waste in the complete absence of oxygen, however, it has been shown that the addition of small amounts of air can enhance biogas production by encouraging the breakdown of substances such as cellulose. This research, however, has usually been done at small scales and without provision to retain the air below the surface of the wastewater. In this research, digesters fed 400-600 grams of poultry litter once weekly were supplied air at 0, 200, 800, 2,000 milliliters per day in 200 milliliter increments evenly spaced throughout the day through a sub-surface manifold with a volume of 380 milliliters. Aeration at 200 and 800 milliliters per day increased biogas production by 14 and 73% compared to digesters receiving no air while aeration at 2,000 milliliters per day decreased biogas production by 19%. The biogas quality (carbon dioxide and methane) was similar in all digesters. Degradation of wood disks placed within the digesters was enhanced by the addition of air.

Technical Abstract: Digestion of animal wastes to produce biogas is often complicated by inherently poor degradation of the feedstocks in anaerobic environments. Research has shown that waste digestion can be enhanced by addition of low levels of aeration that improve degradation of complex substrates without harming microbial populations responsible for methane production. This research, however, has usually been done at small scales and without provision to retain the aeration below the surface of the digestate. In this paper, low levels of aeration was provided to poultry litter slurry though a sub-surface manifold designed to retain air in the sludge layer. Digestate (133 L) was supplied 0, 200, 800, or 2,000 mL air day-1 in 200 mL increments spaced through the day via a manifold with a volume of approximately 380 mL. Digesters were fed 400 g of poultry litter in 4 L water once weekly until day 84 and then 600 g thereafter. Aeration at 200 and 800 mL day-1 increased biogas production by 14 and 73% compared to strictly anaerobic digestion while aeration at 2,000 mL day-1 decreased biogas production by 19%. Biogas quality was similar in all digesters although carbon dioxide and methane concentrations were lowest in the 2,000 mL day-1 treatment. Bicarbonate buffering was slightly higher in digesters receiving supplemental aeration. Increasing feed to 600 g week-1 decreased gas production without affecting biogas quality. Degradation of wood disks placed within the digesters was enhanced by low levels of aeration.