Evaluation of a trickle flow leach bed reactor for anaerobic digestion of high solids cattle manure
Date
2013
Authors
Hanif Abdul Karim, Asma, author
Sharvelle, Sybil, advisor
Carlson, Kenneth, committee member
Davis, Jessica, committee member
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Abstract
Anaerobic digestion (AD) of cattle manure from feedlots and dairies is of increasing interest in Colorado due to its abundant availability. Colorado is the one of the highest producer of high solids cattle manure (HSCM) in the United States. Despite the available resources, Colorado currently has only one operational anaerobic digester treating manure (AgSTAR EPA 2011), which is located at a hog farm in Lamar. Arid climate and limited water resources in Colorado render the implementation of high water demanding conventional AD processes. Studies to date have proposed high solids AD systems capable of digesting organic solid waste (OSW) not more than 40% total solids (TS). Lab tests have shown that HSCM produced in Greeley (Colorado) has an average of 89.6% TS. Multi-stage leach bed reactor (MSLBR) system proposed in the current study is capable of handling HSCM of up to 90% TS. In this system, hydrolysis and methanogenesis are carried out in separate reactors for the optimization of each stage. Hydrolysis is carried out in a trickle flow leach bed reactor (TFLBR) and methanogenesis is carried out in a high rate anaerobic digester (HRAD) like an upflow anaerobic sludge blanket (UASB) reactor or a fixed film reactor. Since leach bed reactors (LBRs) are high solids reactors, studies have indicated clogging issues in LBRs handling 26% TS. Since TFLBRs are subjected to hydrolyze upto 90% TS, obtaining hydraulic flow through the reactor is a challenge. The objective of this research is to (a) ensure good hydraulic flow through the TFLBRs and (b) evaluate and optimize the performance of the TFLBR to effectively hydrolyze the HSCM. The system was operated as a batch process with a hydraulic retention time (HRT) of 42 days without leachate recirculation. A layer of sand was added as dispersion media on top of the manure bed in the TFLBRs. This promoted good hydraulic flow through the reactor eliminating clogging issues. Organic leaching potential of a single pass (without leachate recirculation) TFLBR configuration was evaluated in terms of chemical oxygen demand (COD). Manure is naturally rich in nutrients essential for microbial growth in AD. In a typical MSLBR system, the TFLBRs are subjected to leachate recirculation, conserving the essential nutrients in the system. However, in this single pass system, the leachate removal would flush out the nutrients in the TFLBRs over time. So, nutrient solution was added to the TFLBRs to provide a constant supply of essential nutrients in the reactors for the purpose of this study and would not be necessary in a leachate recirculated TFLBR. A comparison between nutrient dosed and non-nutrient dosed TFLBRs was performed. The non-nutrient dosed and nutrient dosed TFLBRs indicated a COD reduction of approximately 66.3% and 73.5% respectively, in total in terms of dry mass. A total reduction in volatile solids (VS) of approximately 46.3% and 44.7% was observed in the non-nutrient dosed and nutrient dosed TFLBRs, respectively. Biochemical methane potential (BCMP) tests indicated a CH4 potential of approximately 0.17 L CH4/g COD leached and 0.13 L CH4/g COD leached from the non-nutrient dosed and nutrient dosed TFLBRs, respectively. Concentration of inorganics leached from the TFLBR was monitored periodically.
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Subject
anaerobic digestion
biogas
cattle manure
dry digestion
leach bed reactor
methane