Dynamic modelling of bathing water quality with biodegradation of Escherichia coli in TELEMAC-3D

Abstract: Bathing water is of great concern as almost all bodies of water in Sweden today are affected by human activities. Usage of models for bathing water quality may give the possibility to assess and evaluate short-term contamination. The main objective of this thesis was to develop and evaluate a script for degradation of the faecal indicator bacteria Escherichia coli, E. coli, in an aquatic environment. This to deeper understand, predict and identify spreading and degradation of E. coli in bathing water in the future. A literature study focusing on how bathing water quality is classed and how E. coli is degraded in aquatic environments was performed. The literature study formed the basis for an implementation of an exponential first-order degradation model of E.coli in TELEMAC-3D and a performed sensitivity analysis of the used degradation model of E.coli. It has been concluded that the developed script for degradation of E. coli in TELEMAC-3D is operating in accordance with the used exponential first-order degradation model of E.coli. However, there is limited information found of how E.coli is degraded and described mathematically. It was found that the major factors controlling the degradation of E. coli are light intensity at the surface and water temperature. A simplified case with the set-up of an experiment in a form of a simple geometry was modelled. For the simplified case, the results from calculations by hand, a simulation in TELEMAC-3D and the experiment were compared. It could be concluded that the calculations by hand and the simulation in TELEMAC-3D are best correlating with each other, while the experiment differs from the analytical calculations by hand and simulation in TELEMAC-3D. A reason for this might be that information concerning how the experiment was conducted were limited. On the other hand, that the calculations by hand and the simulation in TELEMAC- 3D was correlating shows that the developed script is working in accordance with the used exponential first-order degradation model of E. coli. Overall, it can be said that empirics and research of how E. coli are degraded is restricted and further research is needed to gain a deeper knowledge of bathing water quality.