Anaerobic digestion (AD) of animal manure offers the potential of offsetting the declining natural gas fossil fuel reserves with renewable energy while abating odor and methane greenhouse gas emissions. However, two significant problems must be resolved prior to achieving that potential. Those problems are: 1) the poor economics associated with anaerobic digestion and 2) the release of toxic, greenhouse gas producing, ammonia nitrogen discharged to the atmosphere and groundwater via the anaerobic digestion effluent. The economics of anaerobic digestion can be improved by producing pipeline quality or transportation quality fuel from the biogas1. Production of a pipeline, or transport fuel, requires biogas purification through the removal of water, H2S, and CO2. Existing process are prohibitively expensive. Ammonia gas is toxic, it forms hazardous fine particulate matter (PM2.5) in association with NOx, and is ultimately deposited on land and water altering those ecosystems and undergoing nitrification / denitrification leading to the formation of the GHG nitrous oxide. The Intergovernmental Panel on Climate Change (IPCC) estimates that at least 1% of the ammonia deposited will be be converted to Nitrous Oxide, N2O, a powerful GHG (310 times CO2). This Phase I Small Business Innovation Research project addresses both the adverse environmental emissions (air & water) associated with Anaerobic Digestion (AD) as well as the high cost of producing purified methane gas (biomethane) derived from AD. The SBIR will verify a unique economical process that produces high BTU methane gas while converting ammonia, emitted from the anaerobic digestion process, to a highly valued fertilizer product. Verification will be accomplished through the operation of a series of bench scale ammonia sequestering processes. The project will demonstrate the control of nutrient emissions from animal waste with AD by preventing the loss of ammonia to the atmosphere, reclaiming the ammonia nitrogen resource, reducing fine particulate matter (PM 2.5), and the greenhouse gas emissions of nitrous oxide. The proposed technology will significantly improve the economics of AD by producing a more highly valued methane gas (biomethane) from biogas. The technology will also produce a valuable ammonia nitrogen product, while reducing the salt and nutrient content of the digester's liquid effluent. The proposed process is a component of a US Patent pending for a zero emission anaerobic digestion process (11/771,512). A wide variety of technologies exist to produce pipeline quality methane gas (biomethane) from biogas or to remove ammonia from liquid effluents. All of the current technologies are problematic and expensive. This research will verify a simple, scaleable, economical, low pressure process, that does not require chemical additives, for the reclamation of inorganic nitrogen as a fertilizer while producing high BTU biomethane gas suitable as a transportation fuel. The process will enhance the beneficial use of AD in producing renewable energy and reducing GHG and nitrogen emissions throughout the US. OBJECTIVES: The volatilization of ammonia nitrogen is a serious issue at Confined Animal Feeding Operations (CAFO). Ammonia nitrogen produces a number of adverse environmental and economic consequences. It is a precursor to fine particulate matter (PM 2.5), a regulated air pollutant. It adversely effects animal health and reduces animal weight gain. It is a contributor to greenhouse gas N2O emissions. Its production uses methane gas and produces GHG. It is toxic to anaerobic bacteria and must be removed prior to effluent recycle for the rehydration of high solids manure such as poultry manure. It is a limiting factor in land application of manure and CAFO herd size. On the other hand, ammonia nitrogen is an essential nutrient and has value. Consequently, sequestering ammonia nitrogen to produce a product of value while curtailing unwanted fugitive emissions is of significant value to the public as well as agricultural enterprises. Air resource and water discharge permits will eventually be required by regional authorities. The subject process, once proven, will provide an economical means to obtain permits and market AD biomethane. The process will be adopted by confined animal feeding operations as well as food processors that are interested in reducing their carbon footprint while meeting air and water discharge requirements. It is expected that further research will confirm a reduction in GHG N2O emissions from soil that uses ammonium carbonate as a fertilizer (Hatfield, 2008) Table 1. This research will demonstrate the feasibility of sequestering ammonia nitrogen while improving biogas quality. Two beneficial products will be produced, ammonia nitrogen and biomethane a transportation fuel for dual fuel diesel / biomethane gas engines. In addition to demonstrating the feasibility, a number of significant operating parameters will be established such as: kinetics of carbon dioxide removal, and pH increase by vacuum flotation, stripping efficiency at various gas to liquid flow ratios, ammonium bicarbonate / carbonate precipitation and stability as a function of temperature, gas recirculation flow rate, biogas flow rate and stoichiometry of water, CO2, and ammonia, as well as effluent gas and water quality, etc.
