When is nitrogen recovery from human excreta justified?

This thesis project takes a starting point in the challenges related to nitrogen management in society.

Nitrogen is an essential plant nutrient and a large share of nitrogen fertilisers used today are manufactured by energy-demanding industrial fixation from air. This fixation of nitrogen introduces reactive nitrogen to the societal system which then spills over to natural ecosystems. This process is one of the main drivers behind the transgression of planetary boundaries for biochemical flows of nitrogen (Richardson et al., 2023). Eutrophication issues are evident in many soils and waters, e.g. the Baltic Sea. Nitrogen is also involved in climate change since nitrous oxide is a highly potent greenhouse gas. So, what about capturing and returning more nitrogen from human excreta to agricultural soils? When is that effort justified from a life cycle perspective?

In this project, the nitrogen flows related to human excreta in a selected model region in Sweden will be mapped using earlier research and discussions with experts. This material flow mapping will reveal where nitrogen is lost and in what form. Based on a literature review and discussions with experts, various intervention approaches that will influence these flows will be selected. Scenarios representing these flows will be developed and screening life cycle assessment calculations will be done for the scenarios in order to shed light on hot spots and trade-offs.

This master thesis is suitable for two students that have a bachelor in civil or chemical engineering or global systems and are doing a master in industrial ecology or have good knowledge of wastewater treatment technology and the assessment methods like material flow accounting and life cycle assessment. Mixed backgrounds for the two students can be an advantage.

Examiner and academic supervisor is Prof Magdalena Svanström, Division of Environmental Systems Analysis (magdalena.svanstrom@chalmers.se). Industrial supervisors are Ann Mattsson (Envidan; also adjunct professor at Chalmers) and David Gustavsson (VA SYD). The project is carried out on the platform of VA-teknik Södra: VA-Teknik Södra – Forskning, utveckling och utbildning

References and literature recommendations:

  • Richardson, J., Steffen W., Lucht, W., Bendtsen, J., Cornell, S.E., Donges, J.F., Fetzer, I. et al. 2023. Earth beyond six of nine Planetary Boundaries. Science Advances, 9, 37.