Ammonia recovery from anaerobic digestion via gas-liquid stripping, and its subsequent utilisation in a solid oxide fuel cell for electricity production

The PhD focuses on the removal, recovery and utilization of N from waste streams with both a high N concentration and high organic content, such as manure. Conventionally, these streams are treated through the process of anaerobic digestion, producing biogas of which the CH4 is also considered a potential fuel for a solid oxide fuel cell (SOFC). This project is composed of two research tracks: i) The first idea is to use the produced biogas as a stripping agent, to remove the maximum possible amount of dissolved NH3 gas from the anaerobic digester. ii) The second is to use the biogas as a ammonia carrier, to produce electricity via an SOFC. During anaerobic digestion organically bound N in waste streams is converted into ionized reduced ammonium (NH4+). Dictated by the apparent dissociation constant, ionized NH4+ is in equilibrium with the dissolved NH3 gas. Under alkaline conditions, this equilibrium will shift towards the free NH3 gas, which can be stripped from the solution by a gas flow. The objective of the first research track is to develop an advanced digestion - gas strip technology in which the produced biogas is used for NH3 removal. An additional advantage of N removal through NH3 stripping with biogas as a stripping agent, is that the anaerobic digestion performance itself can be improved by the removal of N since NH3 is a known inhibiting factor for anaerobic digestion. Applying an alkaline digestion process requires fundamental understanding of methanogenesis under high pH conditions and the assessment of pH limits for the overall digestion process using a proper inoculum. Since an alkaline pH facilitates NH3 stripping, detailed studies are required on the organic matter conversion kinetics, NH3 inhibition kinetics, and NH3 gas stripping kinetics at the moderate to alkaline pH range. The excess NH3 enriched biogas is subsequently used in an SOFC for electricity production. The objective of the second research track is to investigate the electrical efficiency, power production and other relevant parameters using the biogas stream containing ammonia as a fuel, for the Solid Oxide Fuel Cell. The foreseen technology is compatible to current full-scale systems, facilitating rapid implementation