Urine is an important resource of crop nutrients, actually having a potential economic value of about three times higher than the nutrients that can be utilised from sludge from conventional wastewater treatment plants (WWTPs), since 80% of the nitrogen and 60% of both the phosphorus and the potassium in the wastewater origins from the urine. Therefore, in new city developments close to existing sewers, a good way to increase nutrient recovery from municipal wastewater is to install urine separation systems.
The urine separation systems of the future will include treatment for volume reduction to decrease needs of transportation and storage volumes and to obtain a concentrated fertiliser. This can, however, counteract the advantages of traditional urine separation (i.e. storage only) compared to conventional wastewater treatment. Volume reduction is very energy-demanding. Furthermore, before volume reduction the urine has to be stabilised to avoid ammonia stripping (nitrogen losses). One promising method is biological nitrification. However, the nitrification process is known to emit the potent greenhouse gas nitrous oxide. Traditional urine separation systems have been shown to decrease the global warming potential of wastewater treatment by 50-60%. How will nitrous oxide emissions from urine nitrification affect the carbon footprint of urine separation?
The aim of this Master’s thesis project is to investigate dynamics of and prevention strategies for nitrous oxide production in a lab-scale moving bed biofilm reactor for urine nitrification.
The lab-scale reactor will be operated at the Department of Chemical Engineering at Lund University. The reactor is a continuous stirred tank reactor and has online measurements of pH, dissolved oxygen and dissolved nitrous oxide concentration and conductivity.