Cryptosporidium Attenuation across the Wastewater Treatment Train: Recycled Water Fit for Purpose

Compliance with guideline removal targets for Cryptosporidium , which do not provide any credit for the inactivation of oocysts through wastewater treatment processes, can considerably increase the cost of providing recycled water. Here we present the application of an integrated assay to quantify both oocyst numbers and infectivity after various treatment stages at three Victorian and two South Australian (SA) Waste Water Treatment Plants (WWTPs). Oocyst density in the raw sewage was commensurate with community disease burden, with early rounds of sampling capturing a widespread cryptosporidiosis outbreak in Victoria. The infectivity of oocysts in sewage was stable throughout the year, but significantly lower at the SA WWTPs. Removals across secondary treatment processes were seasonal, with poorer removals associated with inflow variability; however, no decrease in the oocyst infectivity was identified. For SA WWTPs, those oocysts remaining within the secondary clarified effluent were proportionally more infectious than those in raw sewage. Lagoon systems demonstrated significant inactivation or removal of oocysts, with attenuation being seasonal. Examination of a UV system emphasized its efficacy as a disinfectant barrier but conversely confirmed the importance of a multi-barrier approach with the detection of infectious oocysts post disinfection. The ability to characterise risk from infectious oocysts identified that the risk from Cryptosporidium is significantly less than previously thought and its inclusion in quantitative risk assessments of re-use systems will more accurately direct the selection of treatment strategies and capital expenditure influencing the sustainability of such schemes. IMPORTANCE Here we present the application of a recently developed integrated assay to quantify not only the removal of Cryptosporidium oocysts, but also quantify their infectivity across various treatment stages at five wastewater treatment plants (WWTPs), thereby better measuring the “true effect” of the treatment train on oocyst risk reduction. For a number of the WWTPs analysed in this study the risk is significantly less than previously thought. Therefore, the inclusion of oocyst infectivity into guideline values and in Quantitative Microbial Risk Assessment (QMRA) has the potential to affect future treatment directions and capital expenditure.