Occurrence of Waterborne Protozoa in a Full-Scale Drinking Water Treatment Plant in China by High-Throughput Screening and Genotyping

Abstract

This study investigates potential risk points for waterborne protozoa in a full-scale drinking water treatment plant using high-throughput screening and genotyping. Among 19 protozoan targets of high-throughput quantitative PCR (HT-qPCR), 11 were positive, with Cryptosporidium (22.2%) and Enterocytozoon bieneusi (22.2%) exhibiting the highest detection rates. Three and two protozoan species were detectable in the source water of the reservoir and plant influents, respectively; while no protozoa were detected above the detection limit in plant effluents, as confirmed by both HT-qPCR and an immunofluorescence assay targetingCryptosporidium oocysts and Giardia cysts. Notably, backwash water (from the sand filter and activated carbon filter) and sediment (from the sedimentation tank) samples exhibited higher prevalence and abundance of protozoa. Particularly, backwash water from the sand filter contained eight protozoan targets, with a total abundance of 1.5 × 10⁵ copies/g. Further nested PCR-based genotyping revealed that detected Cryptosporidium parvum belonged to gp60 subtype IIdA19G1 and E. bieneusi was identified as genotype AAE1, suggesting that C. parvum may pose a threat to human health. Overall, the current drinking water treatment process ensures effective protozoan removal in the effluent, but the backwash water and sediment pose potential risk. This study suggested enhancing monitoring and implementing additional measures for key risk points to optimize the prevention and control of waterborne protozoa.