絮凝和软化颗粒对本地孢子UV254失活的影响

Judith Straathof, Zuzana Bohrerova, Natalie M. Hull
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引用次数: 0

摘要

当浊度≤1 NTU时,通常授予美国监管紫外线(UV)消毒信用。然而,研究表明,浊度并不总是与紫外线剂量反应密切相关。本研究考察了饮用水处理厂最坏情况下的高浊度情况对未过滤水源水中原生孢子UV254失活的影响,以及不稳定的絮凝和软化步骤。混凝水(浊度为6.49 ~ 164 NTU)的剂量响应最低,其最大灭活率(kmax = 0.021 cm2/mJ)显著降低,残留种群密度(Nres = 7.081 SFU/mL)较高。原水(kmax = 0.027 cm2/mJ, Nres = 1.168 SFU/mL,浊度= 0.978 ~ 215 NTU)和软化水(kmax = 0.030 cm2/mJ, Nres = 0.216 SFU/mL,浊度= 318 ~ 495 NTU)尽管水质差异显著,但剂量反应相似。颗粒大小和颗粒相关孢子的程度最好地解释了剂量反应的差异。几乎所有孢子都与絮凝颗粒结合,而不是自由漂浮的颗粒,这增加了尾矿,并对紫外线灭活产生了不利影响。根据调控减少等效剂量偏置因子和加标枯草芽孢杆菌孢子的紫外线敏感性,如果紫外线透过率分别≥65%、90%或80%,即使浊度约为1 NTU,隐孢子虫在这些未经处理、絮凝或软化的水中的失活率为4-log。根据颗粒特性,当浊度为1 NTU时,应考虑部分失活信用,以避免高级别违规,同时仍然保护公众健康。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Impact of flocculated and softened particles on UV254 inactivation of indigenous spores

Impact of flocculated and softened particles on UV254 inactivation of indigenous spores

US regulatory ultraviolet (UV) disinfection credit is typically granted when turbidity is ≤1 NTU. However, studies show turbidity does not always correlate well with UV dose responses. This study examined the impact of worst-case high turbidity scenarios at drinking water treatment plants on UV254 inactivation of indigenous spores from unfiltered source water and unsettled flocculation and softening steps. Flocculated water (turbidity = 6.49–164 NTU) had the lowest dose response with a significantly lower Geeraerd-tail maximum inactivation rate (kmax = 0.021 cm2/mJ) and higher residual population density (Nres = 7.081 SFU/mL). Raw source water (kmax = 0.027 cm2/mJ, Nres = 1.168 SFU/mL, turbidity = 0.978–215 NTU) and softened water (kmax = 0.030 cm2/mJ, Nres = 0.216 SFU/mL, turbidity = 318–495 NTU) had similar dose responses despite significantly different water quality. Particle size and the degree of particle-associated spores best explained the differences in dose responses. Almost all spores were associated with flocculated particles instead of free-floating, which increased tailing and negatively impacted UV inactivation. Based on regulatory reduction equivalent dose bias factors and UV sensitivities of spiked Bacillus subtilis spores, Cryptosporidium would be 4-log inactivated in these raw, flocculated, or softened waters if UV transmission were ≥65%, 90%, or 80%, respectively, even though turbidity was grossly >1 NTU. Depending on particle characteristics, partial inactivation credit when turbidity is >1 NTU should be considered to avoid high-tier violations while still protecting public health.

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