Enhancing hydraulic performance of a multi-stage anaerobic digester for high solids cattle manure
Date
2019
Authors
Young, Kadin Catlin, author
Sharvelle, Sybil, advisor
De Long, Susan, committee member
Olsen, Daniel, committee member
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Abstract
Anaerobic digestion is an attractive technology for waste handling because it converts low value waste material into energy and other useful products while performing necessary treatment for proper waste disposal. Conventional anaerobic digestion technology, however, has been met with many economic challenges when being applied to high solids substrate such as dry-lot cattle manure. In Colorado and the rest of the arid west, feedlot practices and dry climate combine to form a waste product that is very high in total solids (TS) content, from 50% up to 90% TS. Since the most common conventional digestion practices typically can only treat wastes up to a maximum of 15% TS, other options must be considered to digest this abundant waste product and convert it to a valuable resource. Research at Colorado State University has led to the development of an innovative multi-stage anaerobic digester (MSAD) technology capable of digesting high solids content waste with very low water addition. The CSU MSAD has demonstrated the ability to successfully digest high solids content waste like that found at the many Colorado feedlots. This system differs from conventional technology in that hydrolysis takes place in one reactor and methane generation takes place in a separate high rate digester. The development of the MSAD for digestion of high solids cattle manure leads to the promising opportunity for valorization of a prevalent waste product in Colorado to create valuable products including methane biogas, compost, and fertilizers. The present research aims to advance the technology by assessing the performance of the MSAD running in a fully linked configuration including each of its individual components: the Upflow Solid-State Hydrolysis Reactor (USSHR), the Leachate Feed Tank (LFT), and the Fixed Film Reactor (FFR). A fully functional Central Leachate Processing System (CLPS) was constructed to demonstrate the technology, to facilitate column scale studies, and to link with the prototype USSHR (P-USSHR) to enable the evaluation of an improved liquid distribution system. The MSAD was constructed at column scale to evaluate the impact on organic leaching potential of varying hydraulic loading rate (HLR) through the USSHR using HLRs of 20, 41, and 75 cm/day for 16-day cycles. This experiment was the first successful demonstration of a fully linked MSAD system using cattle manure as feedstock. It was found that the higher HLR of 75 cm/day yields 25% more COD leached over the 16-day operating period than the two lower loading rates. Additionally, it was found that the P-USSHR achieved notable improvements over the previous operation in hydraulic distribution through the reactor and therefore improved digestion performance and volatile solids destruction, though areas for further improvement were noted.
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Subject
high solids
manure
organic leaching
hydrolysis
anaerobic digestion
multi-stage anaerobic digester