Aeration to improve biogas production by recalcitrant feedstock

Authors: Loughrin, John; Sistani, Karamat; Lovanh, Nanh

Submitted to: Waste to Worth Conference
Publication Type: Proceedings
Publication Acceptance Date: 3/2/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Much agricultural waste is largely composed of polymers such as lignin and complex carbohydrates that are slowly or nearly completely non-degradable in anaerobic environments. An example of such a waste is chicken litter in which wood chips, rice hulls, and sawdust are commonly employed bedding materials. This makes chicken litter a poor candidate for anaerobic digestion because of inherently poor digestibility and, as a consequence, low gas production rates. We built digesters with subsurface manifolds and aerated poultry litter at a rate of 0, 200, 800, or 2,000 mL per day. Tulip poplar wood disks were also added to the digesters to determine if low levels of aeration might enhance their degradation. Adding 800 mL air daily increased biogas production by an average of 73.4% compared to strictly anaerobic digestate. While adding 200 mL of air daily slightly increased gas production, adding 2 L per day decreased gas production by 16.7%. Aerating the sludge improved chemical oxygen demand (COD) with the greatest benefit occurring at 2,000 mL added air per day. As noted, however, this decreased gas production in the control indicating toxicity to the anaerobic sludge. When the tanks were opened, there was widespread fungal growth both on the surface of the digestate and wood disks in aerated tanks whereas non-aerated tanks showed little evidence of fungal growth. While wood disks subjected to all treatments lost significant mass (t-test, a=0.05), disks in the anaerobic tank lost the least amount of weight on average (6.3 g) while all other treatments lost over 7 g weight on average. Results show that low levels of aeration can enhance poultry litter degradation and biogas production.