Compact wastewater treatment by aerobic granular sludge – performance at low temperatures

Research Project, 2021 – 2022

The overall purpose of this study is to increase the understanding of how the aerobic granular sludge (AGS) technology can be implemented at conditions typical for Nordic conditions with low wastewater temperatures. The AGS technology has gained a lot of interest due to its many advantages such as being very compact, requires less energy since less pumping is required compared to conventional activated sludge processes and it also uses less energy. Even though full-scale AGS installations exist in many parts of the world, few detailed studies have been performed to assess its performance at conditions typical for Nordic conditions with cold wastewater temperatures in the winter. Other challenge are the strict discharge limits for organic matter and nutrients here in Sweden for example.  It is therefore important to investigate how the process performs when the operational conditions are changing due to seasonal variations in wastewater temperatures. To be able to increase the understanding of the granulation process and what determines the degradation processes, detailed studies in controlled environments are essential. Since the efficiency of the AGS technology is dependent on the granule size and structure, investigations of the microbial community present as well as their spatial organization at different operational conditions are important.

In a previous project we have studied the start-up of the first full-scale AGS process in Sweden, the Österröd WWTP in Strömstad. A PhD student, Jennifer Ekholm, has been connected to this project. As many process parameters interact in a complex manner in a full-scale treatment plant. There are seasonal variations in wastewater composition, flow and temperature. On top of this the operational strategies have been frequently changed. This makes it hard to assess what effects different process parameters actually have on the granules in the system. Therefore, controlled experiments in laboratory-scale systems give valuable information about the various mechanisms involved in the process.