Fate and Transport of Fecal Bacteria in Rivers after Combined Sewer Overflows

The central theme of this project is to investigate the interrelationship of transport processes in flowing waters and the processes which occur within local biocenoses. More specifically, the interaction of pathogenic bacteria in the bulk phase, resulting from fecal contamination, and the benthic biofilm will be examined for the Isar River. The fundamental processes will be quantified through lab and field experiments. Finally, the results will be incorporated into a mathematical model for simulation of the fate and transport of indicator bacteria.

Previous research has shown that biofilms can enhance the retention of pathogenic bacteria in drinking water systems. However, until now there have been only limited studies regarding the role of benthic biofilms in retaining pathogens in flowing waters such as rivers or streams. In comparison to the bulk phase of a water body, the biofilm provides an increased amount of nutrients and carbon (humic substances). Moreover, it serves as a protection for microorganisms from UV irradiation and the flow conditions of the bulk phase. Thus, it is plausible that these favorable conditions could lead to the development of a reservoir of pathogens within benthic biofilms.

With the help of a lab-scale flume (length = 1 m, width = 0.1 m), confocal laser scanning microscopy (CLSM), and particle image velocimetry (PIV), the transport of bacteria from the bulk phase to the biofilm as well as the fate of the bacteria within the bulk phase and biofilm will be clarified. Additionally, indicator bacteria (E. coli and Enterococci) will be quantified through a variety of techniques including microtiter tests and Real-time PCR. In addition to the lab-scale flume, a larger flume (length = 10 m, width = 0.5 m) will be operated during the summer months to determine the sedimentation rate and distribution of E. coli and Enterococci.

The results obtained from the lab-scale flume will be used for the development of a mathematical model describing the key transport processes of indicator bacteria in flowing waters. In the end, the model will depict the fate of indicator organisms and thus, the probable load of pathogens in a river characterized by having a rocky bed. The results of the large-scale flume experiments will be used for model validation.

Project Leader Prof. Dr. rer. nat. Harald Horn
Researcher Dr.-Ing. Evelyn Walters
Funding Deutsche Forschungsgemeinschaft (DFG)