University of Campinas - School of Civil Engineering, Architecture and Urban Design - Department of Infrastructure and Environment, Avenida Albert Einstein, 951 -Cidade Universitária, 13083852 Campinas, SP, Brazil.
University of Campinas - School of Civil Engineering, Architecture and Urban Design - Department of Infrastructure and Environment, Avenida Albert Einstein, 951 -Cidade Universitária, 13083852 Campinas, SP, Brazil.
Environ Pollut. 2020 Nov;266(Pt 3):115144. doi: 10.1016/j.envpol.2020.115144. Epub 2020 Jul 6.
Giardia is a protozoan parasite of primary concern for the drinking water industry. High contact times are required for Giardia inactivation by chlorination, while ozonation may be effective at much lower Ct products. In this study, we have assessed the occurrence of Giardia cysts in raw water, and in chlorinated or ozonated water from a drinking water treatment plant (DWTP) in Brazil, over a 16-month period. Moreover, we analyzed the effects of primary disinfection on cysts, and calculated the infection risk caused by the occurrence of Giardia cysts in raw water, chlorinated or ozonated water. Furthermore, we assessed the correlation of Giardia cysts with indicator bacteria in raw water. Data referring to concentration of Giardia cysts in raw water showed adherence to a gamma distribution at a significance level α = 0.05. The detection frequency and the mean concentration of Giardia cysts were higher in raw water (86.6%, 26 cysts∙L), than in chlorinated (46.1%, 15.7 cysts·L) or ozonated water (43.5%, 11.1 cysts·L). Overall, Giardia non-viable cysts were detected more frequently in ozonated water (80%) than in chlorinated water (68.2%) or raw water (37.7%). Ozonation and chlorination resulted, respectively, in ≈27.5- and ≈13- fold reduction of Giardia infection risk, when compared to the risk calculated for raw water. Total coliform and Escherichia coli proved to be suitable surrogates to predict the occurrence of Giardia cysts in raw surface water, however, the indicator bacteria may not be suitable surrogates to predict the disinfection of Giardia cysts, as no correlation was found between indicator bacteria and Giardia cysts in treated water. To our knowledge, this is the first study reporting the efficacy of chlorine and ozone at Ct products actually applied at a full-scale drinking water treatment plant against Giardia cysts naturally occurring in the source water, i.e. real situation. Ozonation has proven more efficient than chlorination against Giardia cysts in surface water. Escherichia coli proved to be suitable surrogate to predict Giardia cysts in raw surface water.
贾第鞭毛虫是一种原生动物寄生虫，主要引起饮用水行业的关注。氯消毒需要较长的接触时间才能有效灭活贾第鞭毛虫，而臭氧消毒在较低的 Ct 值产品下可能有效。在这项研究中，我们在 16 个月的时间里评估了巴西一家饮用水处理厂（DWTP）原水、氯化或臭氧处理水中贾第鞭毛虫包囊的发生情况。此外，我们分析了原水初级消毒对包囊的影响，并计算了原水、氯化或臭氧处理水中贾第鞭毛虫包囊的发生对感染风险的影响。此外，我们还评估了原水中贾第鞭毛虫包囊与指示菌的相关性。原水中贾第鞭毛虫包囊浓度数据符合在 0.05 显著性水平下服从伽马分布。原水中贾第鞭毛虫包囊的检出频率和平均浓度（86.6%，26 个包囊·L-1）均高于氯化（46.1%，15.7 个包囊·L-1）或臭氧处理水（43.5%，11.1 个包囊·L-1）。总体而言，臭氧处理水中非活性贾第鞭毛虫包囊的检出频率（80%）高于氯化（68.2%）或原水（37.7%）。与原水相比，臭氧和氯化处理分别将贾第鞭毛虫感染风险降低了约 27.5 倍和 13 倍。总大肠菌群和大肠杆菌被证明是预测原地表水贾第鞭毛虫包囊发生的合适替代指标，但指示菌可能不适合预测贾第鞭毛虫包囊的消毒效果，因为在处理水中未发现指示菌与贾第鞭毛虫包囊之间存在相关性。据我们所知，这是第一项报告氯和臭氧在实际应用于大规模饮用水处理厂的 Ct 值产品对天然存在于水源水中的贾第鞭毛虫包囊的功效的研究，即真实情况。臭氧处理对地表水贾第鞭毛虫包囊的效果优于氯化。大肠杆菌被证明是预测原地表水贾第鞭毛虫包囊的合适替代指标。
