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

Abstract

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 levels after various treatment stages at three Victorian and two South Australian (SA) wastewater 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 level of infectivity of oocysts in sewage was stable throughout the year but was 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 treatment-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 multibarrier approach with the detection of infectious oocysts postdisinfection. The ability to characterize risk from infectious oocysts revealed that the risk from Cryptosporidium is significantly lower than previously thought and that its inclusion in quantitative risk assessments of reuse 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 not only to quantify the removal of Cryptosporidium oocysts but also to 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 analyzed in this study the risk, is significantly lower than previously thought. Therefore, the inclusion of oocyst infectivity in guideline values and in quantitative microbial risk assessment (QMRA) has the potential to affect future treatment directions and capital expenditure.KEYWORDS cryptosporidiosis, Cryptosporidium, reuse water, oocyst infectivity, wastewater treatment R eusing water traditionally seen as wastewater can provide additional sources of the resource while also reducing unwanted inputs into the environment (1, 2). Nevertheless, it is paramount that the health of both the public and the environment is protected, as reuse water has the potential to pose a high risk from viruses, bacteria, and protozoans (1, 3, 4). Therefore, water destined for reuse must be treated accordingly and be fit for purpose (5). The protozoan parasite Cryptosporidium is problematic

Wastewater-based epidemiology—surveillance and early detection of waterborne pathogens with a focus on SARS-CoV-2, Cryptosporidium and Giardia

“…The removal of Cryptosporidium and Giardia (oo)cysts at WWTPs can be highly variable and often dependent on the temperature and type of wastewater treatment processes used (Emelko 2003 ; Nasser et al 2012 ; 2016; King et al 2017 ; Hamilton et al 2018 ; Schmitz et al 2018 ). Seasonality and inflow also affect removal (King et al 2017 ), and many studies have reported variable removal of both Cryptosporidium and Giardia from WWTPs, particularly activated sludge (Nasser et al 2012 ; 2016).…”

“…The removal of Cryptosporidium and Giardia (oo)cysts at WWTPs can be highly variable and often dependent on the temperature and type of wastewater treatment processes used (Emelko 2003 ; Nasser et al 2012 ; 2016; King et al 2017 ; Hamilton et al 2018 ; Schmitz et al 2018 ). Seasonality and inflow also affect removal (King et al 2017 ), and many studies have reported variable removal of both Cryptosporidium and Giardia from WWTPs, particularly activated sludge (Nasser et al 2012 ; 2016). Giardia Log 10 reduction values (LRV) removal efficiencies of 0.5–4.0 (Taran-Benshoshan et al 2015 ; Soller et al 2017 ; Hamilton et al 2018 ; Yamashiro et al 2019 ) and Cryptosporidium LRVs ranging from 0.21 to 3.08 (King et al 2017 ; Soller et al 2017 ; Hamilton et al 2018 ) have been reported from various WWTPs.…”

Cryptosporidium and Giardia in Wastewater and Surface Water Environments

“…A QMRA conducted by Chaudhry et al (2017) estimated 1.58 ± 1.3 log removal values (LRVs) for Cryptosporidium from a conventional wastewater treatment process of sedimentation, activated sludge, and filtration according to data reported by Ottoson et al (2006). The LRVs for Cryptosporidium in five wastewater treatment plants ranged from 0.21 to 3.08 (King et al, 2017), and Soller et al (2017) estimated between 0.70 and 1.5 LRVs of Cryptosporidium due to the conventional wastewater treatment in another QMRA. For drinking water, a general Cryptosporidium LRV was estimated as 2 ± 0.5 for processes of coagulation, flocculation, sedimentation, and filtration (Chaudhry et al, 2017) according to data in Harrington et al (2003).…”

Biological HRPs in wastewater

“…It can be seen that pathogenic protozoa are the main causes of waterborne diseases among various pathogenic microorganisms. Table 3.4 summaries the common pathogenic protozoa lived in different types of wastewater (Cacciò et al, 2003;Ferrari et al, 2006;Hench et al, 2003;King et al, 2017;Sukprasert et al, 2008).…”