Lay summary


Novel decentralized reactors can be the key to a more efficient and affordable wastewater treatment. This project investigates, whether a novel biological process – nitritation/anammox – can be used to remove nitrogen in small on-site reactors.



Combining sewers and centralized wastewater treatment has worked reasonably well for the industrialized part of the world, but for a number of reasons the success in developing and fast industrializing countries has been very limited. Recent research has shown that separation of wastewater streams at the source and decentralized treatment would be more resource-efficient, cheaper and easier to implement. Especially the separate treatment of urine would strongly reduce environmental pollution. Lately, a biological process – one-stage nitritation/anammox – has been implemented in some wastewater treatment plants to remove nitrogen more efficiently from digester supernatant than conventional processes. Our laboratory experiments have shown that the process can also be used to remove nitrogen from urine, but the experiments also revealed that small changes in the operational parameters can lead to a persistenly low performance. Our first study suggests that the decrease in performance coincided with a regime shift of the microbial population.



In this follow-up study, we conduct well-controlled experiments to elucidate the main reasons for the regime shift. The main focus is on biodegradable organic substances. In well-controlled experiments, we investigate how the ratio of biodegradable substances to ammonia influences the activity of the nitrogen removing bacteria. Additionally, we analyze, whether specific organic substances inhibit nitrogen removing bacteria. Finally, we will test whether upstream removal of the organic substances leads to a more stable operation of the nitritation/anammox reactor.



The overall goal of the project is to determine optimal conditions for stable biological nitrogen removal from urine in small on-site reactors. Our study will also result in a better understanding of the influence of organic substances on nitritation/anammox processes.



Decentralized reactors for nutrient removal can be essential tools to fight the deterioration of aquatic environments worldwide. Biological processes such as nitritation/anammox could be energy-efficient options for nutrient removal, but operating such processes in small on-site reactors requires precise process control and in-depth understanding of the critical influence factors.

Many researchers and practitioners have experienced that high contents of biodegradable organic substances can be problematic for the nitritation/anammox process, therefore the results will be interesting for other process applications beyond urine treatment.