Experimental evaluation of ammonia extraction via vacuum membrane distillation from waste water streams

Ammonia is a potential hydrogen vector that is looked upon as an alternate source to produce hydrogen for energy generation particularly in the transport sector. Large percentage of ammonia is bound in various wastewater streams such as biogas digestate, slaughterhouse waste and in the municipal waste water treatment plants. By applying vacuum membrane distillation technology, it is possible to obtain pure ammonia from these waste streams that could feed a solid oxide fuel cell to generate electrical power. The project “AmmoniaُtoُPower” is an Austrian national research project conducted by three groups. AEE INTEC is involved in the development and experimental evaluation of a pilot vacuum membrane distillation plant while AVL List GmbH in collaboration with Technische Universität Graz, are responsible for development of the solid oxide fuel cell. Under the framework of this project, an experimental comparison between direct contact and vacuum membrane distillation was performed using artificial ammonium salt water. In addition, the effect of changing feed ammonium concentration on the ammonia flux, ammonia to total flux ratio and thermal energy consumption was also analyzed by conducting experiments using artificial ammonium salt in vacuum membrane distillation. In the end, feed from Gleisdorf wastewater treatment plant was used to analyze the ammonia separation performance in vacuum membrane distillation. From the results of these experiments it was found that ammonia fluxes from vacuum membrane distillation outperform those from direct contact membrane distillation reaching a value of 2.0 kg/m2 /h at feed ammonium concentration of 10g/L. The transmembrane pressure was found to be the most influential parameter defining ammonia flux under varying feed ammonium concentrations, and these results were compared with a mathematical model also. The feed from Gleisdorf wastewater treatment plant produced about 0.15 kg/m2 /h of ammonia flux under 50oC feed temperature with a thermal energy consumption equal to 100 kWh/kg of ammonia produced