The main sewer as reactor

Integrated system

The goal of this project is to obtain a fundamental understanding of the biological processes in the sewer and to evaluate the role the sewer can play in an integrated approach of urban (waste) water management.

The sewer system – the most expensive part of the urban drainage system – is regarded by most people as a simple transport system. However, the wastewater composition at different locations is normally similar, but it has a different and variable composition when it reaches the wastewater treatment plant (WWTP). This indicates that biological, chemical and physical processes take place, altering wastewater properties (Figure 1). A reduction in the amount of oxygen binding components (COD) in the wastewater would relieve the treatment plant. But the degradation of easily degradable material could also hamper nitrogen and phosphorus removal.

Figure: Interactions and processes in the sewer system. The enlargement shows the structure and composition of sewer biofilm schematically.

Bacteria as workforce

Bacteria are mainly responsible for the convertion processes. Most of them are found in the biofilm (slime layer) on the sewer wall. Although they have to invest energy and resources to build up the biofilm, it enables them to get settled in environments where they would be flushed away otherwise. Erosion of the biofilm constantly supplies the wastewater with bacteria, increasing the amount of active bacteria. Within this project ('The main sewer as reactor'), the biofilm and its interactions with wastewater are studied.

Sewer biofilm research

The measurements are taking place in a two kilometre long section of the main sewer between two villages. Biofilm growth and activity, and changes in wastewater composition are being measured.