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ANAEROBIC DIGESTION OF POULTRY MANURE: IMPLEMENTATION OF AMMONIA CONTROL TO OPTIMIZE BIOGAS YIELD

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Title: ANAEROBIC DIGESTION OF POULTRY MANURE: IMPLEMENTATION OF AMMONIA CONTROL TO OPTIMIZE BIOGAS YIELD
Author: Farrow, Cameron
Department: School of Engineering
Program: Engineering
Advisor: McBean, Ed
Abstract: Anaerobic digestion of poultry manure has been historically challenging, and infrequently implemented on a full scale, due to the high total solids (TS) and high ammonia content of the substrate. Conventional digestion processes require extensive substrate dilution in order to employ liquid-phase pumping systems and reduce the risk of ammonia accumulation. The necessary substrate dilutions result in an economically infeasible process. Anaerobic leaching bed reactors (ALBRs), coupled with a strategy for ammonia removal, provide a solution to both issues. ALBRs are utilized to maintain digester homogeneity without an active mixing regime. Struvite precipitation is employed concurrently with digestion to reduce total ammoniacal nitrogen (TAN) and prevent inhibition of methanogenic archaea. Nutrient distribution is achieved by recirculation of the percolate through the substrate, enabling the utilization of high solids feedstocks. Partitioning leachate from the bulk substrate allows ammonia removal methodologies to be employed without disturbing anaerobic archaea. Investigations reported herein characterize the influence of moisture content, TAN and temperature on biogas yield during poultry manure digestion. High solids digestion is shown to be most efficient in mesophilic temperature ranges with influent total solids (TS) between 15% and 25%. Digestion at thermophilic temperatures demonstrates increased ammonia inhibition, in contrast to mesophilic digestion. Co-digestion of poultry manure with grease and corn silage demonstrate increased biogas yields of 22% and 44%, respectively, in comparison to digestion of poultry manure alone. The impact of phosphate and magnesium additives, pH, temperature and the N:Mg:P molar ratio on struvite precipitation efficacy are quantified. Magnesium chloride (MgCl2·6H2O) and monopotassium phosphate (KH2PO4) are shown to be the most efficient combination of additives for TAN reduction of poultry manure leachate under neutral reaction conditions. Precipitation is shown to progress efficiently at a pH of seven, in contrast to the commonly reported optimum of nine. Thus allowing leachate treatment without disturbing the microbial consortium. Results reported herein evidence an increase in biogas yield of 30% during batch digestion trials and an increase of 235% during semi-continuous trials, when employing struvite precipitation methodologies. Methane content of the biogas is also shown to increase significantly (p<0.05), when employing struvite precipitation.
URI: http://hdl.handle.net/10214/9657
Date: 2016-05
Citation: Farrow, C., Crolla, A., Kinsley, C., McBean, E. (2015). Influence of temperature and ammonia on the high solids co-digestion of poultry manure. Applied Engineering in Agriculture, 31(4), 535-542.


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