[Frontiers in Bioscience E3, 1300-1309, June 1, 2011]

Dispersion of Legionella-containing aerosols from a biological treatment plant,Norway

Janet Martha Blatny1, Hannibal Fossum1, Jim Ho2, Murat Tutkun1, Gunnar Skogan1, Oyvind Andreassen1, Else Marie Fykse1, Viggo Waagen3, Bjorn Anders Pettersson Reif1

1Norwegian Defence Research Establishment (FFI), P. O. Box 25, N-2027 Kjeller, Norway, 2Defence Research and Development Canada (DRDC), Suffield, Box 4000, Medicine Hat, Alberta, T1A 8K6, Canada, 3Borregaard Ind. Ltd., P. O. Box 162, N-1701 Sarpsborg, Norway

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Materials and methods
3.1. Monitoring site and weather conditions
3.2. Monitoring particle distribution in air
3.3. Sampling and growth of Legionella
3.4. Computational fluid dynamics
3.5. Wind tunnel experiments
4. Results
4.1. Particle concentration
4.2. Particle size distribution
4.3.Legionella in air samples
4.4. Near-field transport
4.5. Aerosol ground deposition
5. Discussion
6. Acknowledgement

1. ABSTRACT

Legionella was detected in aeration ponds (biological treatment plant) at Borregaard Ind. Ltd., Norway, and in air samples harvested directly above these ponds. Since 2005, three outbreaks of legionellosis occurred within a 10 km radius from this plant. This work addresses the dispersion patterns of Legionella-containing particles by characterizing the aerosol plume emitted from these ponds (outbreak source) < 500 meters using wind-tunnel measurements, CFD simulations, and real-life measurements. The most abundant particles directly over the ponds were < 6 and >15 µm. The results showed that the aerosol plume remained narrow; 180 meters wide at 350 meters downwind of the ponds, and that 2 and 18 µm aerosols were mainly deposited in the vicinity of the ponds ( 150 - 200 meters). Furthermore, the maximum aerosol concentration level appeared 5-10 meters above ground level and the maximum concentration 500 meters downwind was approximately 2% of the concentration level directly above the ponds. Our study demonstrates the strength of combining modeling with real-life aerosol analyses increasing the understanding of dispersion of airborne (pathogenic) microorganisms.