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.

摘要

水传播疾病是公共卫生系统的一个相关问题，因为常用的处理技术可能无法去除所有的水污染物。隐孢子虫属 卵囊在水处理厂中是一个问题，因为它们的尺寸减小并且对消毒过程（例如氯化）有抵抗力。此外，保留在过滤介质上的卵囊可能会在过滤器反冲洗水 (FBW) 中再循环。本研究旨在检测隐孢子虫在 FBW 上人工接种卵囊并评估臭氧处理性能。合成的 FBW 经历了三种浓缩方法，然后是免疫磁分离：碳酸钙絮凝、直接离心和使用 7X ICN 分散溶液直接离心。选择后一种方法是因为它对卵囊活力的干扰较小（降低 37.2%），并且在初步测定中回收率较高（22.1%）。商业悬浮液的回收率为 15.4 ± 3.3%，尽管使用 EasySeed® 悬浮液进行的分析质量获得了 2.8 ± 0.8% 的回收率。由于回收率低，尤其是在复杂基质中，这些原生动物检测的局限性和方法具有挑战性。最后，在中试规模上进行了 FBW 臭氧化，碘化丙啶染料表明处理后卵囊活力降低。对于 7.5 mg O的剂量，卵囊失活为 2.83 log 和 3.44 log₃ L ^-1 10分钟（即75 mg min L ^-1）和10 mg O ₃ L ^-1 5分钟（即50 mg min L ^-1）。消毒是应对疫情爆发的重要途径，臭氧处理应进一步研究。