Quantitative Microbial Risk Assessment to determine pathogen risks for a Managed Aquifer Recharge project

Declan Pagea, Simon Tozeb, Elise Bekelec, and Jatinder Sidhub

aCSIRO Water for a Healthy Country, Private Bag No 2, Glen Osmond, SA 5064, Australia
bCSIRO Water for a Healthy Country, Queensland Bioscience Precinct, 306 Carmody Road, St Lucia, Brisbane, QLD 4067, Australia
cCSIRO Water for a Healthy Country, CSIRO Centre for Environment and Life Sciences, Private Bag No 5, PO Wembley, WA 6913, Australia

With the release of the Australian Guidelines for Water Recycling: Managed Aquifer Recharge (MAR), aquifers are now being included as a treatment barrier when assessing risk of recycled water systems. A MAR research site recharging secondary treated wastewater in an unconfined carbonate aquifer was used in conjunction with a Quantitative Microbial Risk Assessment (QMRA) to assess the microbial pathogen risk in the recovered water. The assessment involved undertaking a detailed hydrogeological assessment of the aquifer at the MAR site and determining the decay rates of reference pathogens from an in-situ decay study. These factors along with literature data for the other treatment barriers were then used in the QMRA which demonstrated that the recovered water at this site did not meet the Australian Guidelines for recycled water when used for differing private green space irrigation scenarios (DALYs < 1 ´ 10-6). The results also confirmed the importance of obtaining local hydrogeological data as local heterogeneity can influence residence time in the aquifer which, in turn, influences the outcomes. QMRA can be used to determine the residual risk from pathogens in recovered water and showed that it can be a valuable tool in the preliminary design and operation of MAR systems (a pre-commissioning risk assessment) and the incorporation of complementary engineered treatment processes to ensure that there is acceptable health risk from the recovered water for a variety of uses.

Technical category: Risk assessment and uncertainty