Ammonia Recovery and Biomethane Production from Concentrated Manure

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.