CFD modelization of Legionella’s atmospheric dispersion in the explosive outbreak in Murcia.

Abstract

Cooling towers, among other equipments, could have an important atmospheric impact, becoming a source of pollutants or biological agents. The most important, due to its frequency and importance of the outbreaks, is Legionella. Since its discovery in 1976 in Philadelphia, where the total number of cases reached more than 200 of those more than 30 died, several outbreaks have been reported causing tens of deaths. The most important one due to its spread took place in the city of Murcia (Spain), in 2001, with more than 600 cases and where 23 out of 70 investigated cooling towers were positive to Legionella Pneumophila. In the present work, a validated numerical modelization using the Computational Fluid Dynamics (CFD) code ANSYS Fluent is employed to simulate the dispersion of the drift from the cooling tower causative of the outbreak in the real urban environment of Murcia in the days of highest emissions, which are located by means of the number of infections given by the epidemic curve. The results of the modelization are compared with the results of the epidemiological investigation carried out by the Epidemiology Service at the Consejería de Sanidad de Murcia. The main objective of this modelization is to predict a cooling tower influence area, what will help to reduce environmental and personal impact in case of an eventual infection of its water, or, as it is used in here, to improve the resources used to find the focus of infection after an outbreak has taken place. The modelization was previously validated using data from an experimental cooling tower installation. The data set that was measured includes cooling tower parameters such as water and air flow, inlet and outlet water and air temperature, atmospheric conditions (by means of a meteorological tower and meteorological station) but also droplet diameter at the cooling tower outlet and droplet deposition in the surroundings using the water sensitive paper technique. Several cases were employed to validate the modelization, including a wide range of atmospheric conditions and cooling tower configurations.