Aerosolization of Aspergillus niger spores from growing colonies on a bare tube

Abstract

Aerosolization of fungal spores from the cooling coils of a heating, ventilating and air conditioning (HVAC) system can cause adverse health effects. As air sweeps across a coil, it may accelerate and decelerate, and the resulting spore detachment may vary according to the position of the fungal colonies on the coil in relation to the airflow. This study used a circular tube in a wind tunnel to represent a single coil. The aerosolization of Aspergillus niger spores from a colony in a carved groove along the longitudinal direction of the tube was investigated. Growing colonies at four different positions on the tube surface were subjected to blowing air. The airflow surrounding the circular tube was numerically solved to estimate the drag force necessary to detach the spores. The results revealed that the quantities of collected airborne spores when the colonies were positioned tangentially to the incoming airflow were four to 12 times those when the colonies were aligned with the airflow under the threshold blowing air speeds. The local air speeds at the height of the growing fungi could differ greatly from the inlet mainstream air speed. This difference should be taken into account in estimations of the drag force required to aerosolize the fungal spores on the tubes.