Detection of Cryptosporidium Parvum Oocysts in Artificially Contaminated Filter Backwash Water and Ozone Treatment at Pilot Scale

ABSTRACT Waterborne diseases are a relevant concern for public health systems since commonly applied treatment techniques may not remove all water contaminants. Cryptosporidium spp. oocysts are an issue in water treatment plants due to their reduced size and resistance to the disinfection process (e.g., chlorination). Moreover, oocysts retained on the filter media might recirculate amongst the filter backwash water (FBW). This study aimed to detect Cryptosporidium parvum oocysts artificially inoculated on the FBW and evaluate the ozone treatment performance. A synthetic FBW underwent three concentration methods followed by immunomagnetic separation: calcium carbonate flocculation, direct centrifugation, and direct centrifugation with the 7X ICN dispersion solution. The latter method was selected as it presented less interference on oocyst viability (37.2% reduction) and higher recovery (22.1%) on preliminary assays. The recovery for the commercial suspensions was 15.4 ± 3.3%, although the analytical quality performed with EasySeed® suspension obtained a recovery of 2.8 ± 0.8%. These limitations and methodologies for protozoan detection are challenging due to low recoveries, especially in complex matrices. Finally, FBW ozonation was performed on a pilot scale, and the propidium iodide dye indicated oocyst viability decreased after treatment. Oocyst inactivation was 2.83 log and 3.44 log for dosages of 7.5 mg O3 L−1 for 10 min (i.e., 75 mg min L−1) and 10 mg O3 L−1 for 5 min (i.e., 50 mg min L−1), respectively. Disinfection is a crucial pathway for addressing outbreak scenarios, and ozone treatment should be further studied. Graphical abstract