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The economical A2 digester – anaerobic digestion followed by composting in the same vessel

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131669191,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   Conly L Hansen, Sharon Baker Johnson, Russell V. Davis
Keywords:   Anaerobic digesters solid anaerobic digestion animal wastes plastic film composting.

Abstract. The use of anaerobic digestion on US dairies is considered to be economical for over 500 cows, yet most US dairies have fewer than 500 cows. This project featured a low cost polyethylene tube bioreactor wherein both anaerobic digestion and aerobic composting could take place; thus the name A2 digester. The A2 can be built in a few hours and is economical and appropriate for some dairies. In the A2, high solids anaerobic digestion takes place followed by composting. By capturing and burning methane a farmer can sell carbon credits if replacing lagoon storage of raw manure. This paper reports the first experimental trial for the A2 digester. The polyethylene material was not thick or dense enough to prevent leaks. Still, 36% of COD was removed in the anaerobic digestion process operated at ambient temperature. Biogas was over 55% methane. Total COD removal with anaerobic digestion and composting was 57.5%.

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