Assessing the risk of legionella exposure in groundwater treatment plants

Aeration systems used in groundwater treatment plants are perceived as a potential source of Legionella exposure, an opportunistic pathogen of significant public health concern. Building on the Legionella High Level Risk Assessment Initiative (LHLRAI) developed by Water Corporation Western Australia, a team of researchers at UNSW, led by Pierre Le-Clech from the School of Chemical Engineering, aims to further quantify the potential of Legionella exposure.

While the study was initiated in 2018 with the characterisation of fouling samples from seven aerators, recent activities have included the development of a more robust assessment of risk. Guided by the LHLRAI, sampling analysis, and site observations, Legionella exposure risk was modelled using Bayesian Networks (BN). The input variables – nutrient availability, stagnant water, system deficiencies, and location and access, as well as their associated weighting scores – were represented in the BN model. This initial assessment demonstrates the potential of BN modelling to improve risk assessments that support practical decision-making (especially in terms of monitoring) in managing Legionella exposure.

Another important step of this project includes the upcoming construction of a pilot aerator to be installed in one of Water Corporation’s sites in Western Australia. The design of the aerator has incorporated a number of improvements to limit the growth and transmission of Legionella to operators. A series of experiments and assessment will soon be completed to provide further advices to stakeholders on how to best operate and maintain aerators in the industry. It is expected that those recommendations will be highly relevant to the operation and maintenance of other air-handling systems like cooling towers, which have been identified to be at risk of producing pathogens of concerns too.