Ammonia - from pollutant to power

Abstract

Ammonia (NH3) is one of world’s most-produced chemicals and is mostly used as a raw resource for fertilisers. From the used NH3-based fertilisers, almost half of the NH3 ends up in receiving water bodies, leading to eutrophication, eventually resulting in species diversity loss in the aquatic environment. To minimise environmental damage, total ammoniacal nitrogen (TAN) should be removed from residual waters before discharge. Currently, the treatment of residual waters with high TAN concentrations (hereafter nitrogen (N)-loaded residual waters) by biological processes, such as partial nitritation in combined with anammox (reaching TAN removal efficiencies up to 90%), is challenged by the undesired emission of oxidised nitrogen species. In addition, current methods to recover TAN from N-loaded residual waters for reuse purposes require large amounts of energy and chemicals. Interestingly, NH3 was recently acknowledged as a carbon-free carrier of energy, having an energy content of 21 MJ∙kg-N-1. The fact that NH3 carries energy, opens possibilities to remove TAN from N-loaded residual waters and subsequently recover NH3 for the generation of electricity, potentially leading to energy-positive methods to remove TAN from N-loaded residual streams. The objective of this thesis was to assess the feasibility to achieve competitive (approximately 90%) TAN removal from N-loaded residual waters and to use the recovered NH3 for electricity generation purposes, using a combination of technologies without using chemicals. The used technologies in this thesis are electrodialysis (ED), bipolar membrane electrodialysis (BPMED), vacuum membrane stripping (VMS) and a solid oxide fuel cell (SOFC). To determine the suitability of the combination of technologies, the research conducted in this thesis focused on the mass transfer and achievable concentrations of the various TAN species (ammonium (NH4 +), dissolved NH3 and gaseous NH3), as well as the electrical energy aspects (consumption and generation) for the various technologies…