Judith Straathof, Zuzana Bohrerova, Natalie M. Hull
{"title":"絮凝和软化颗粒对本地孢子UV254失活的影响","authors":"Judith Straathof, Zuzana Bohrerova, Natalie M. Hull","doi":"10.1002/aws2.70010","DOIUrl":null,"url":null,"abstract":"<div>\n \n \n <section>\n \n <p>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 UV<sub>254</sub> 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 (<i>k</i><sub>max</sub> = 0.021 cm<sup>2</sup>/mJ) and higher residual population density (<i>N</i><sub>res</sub> = 7.081 SFU/mL). Raw source water (<i>k</i><sub>max</sub> = 0.027 cm<sup>2</sup>/mJ, <i>N</i><sub>res</sub> = 1.168 SFU/mL, turbidity = 0.978–215 NTU) and softened water (<i>k</i><sub>max</sub> = 0.030 cm<sup>2</sup>/mJ, <i>N</i><sub>res</sub> = 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 <i>Bacillus subtilis</i> spores, <i>Cryptosporidium</i> 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.</p>\n </section>\n </div>","PeriodicalId":101301,"journal":{"name":"AWWA water science","volume":"6 6","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/aws2.70010","citationCount":"0","resultStr":"{\"title\":\"Impact of flocculated and softened particles on UV254 inactivation of indigenous spores\",\"authors\":\"Judith Straathof, Zuzana Bohrerova, Natalie M. Hull\",\"doi\":\"10.1002/aws2.70010\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div>\\n \\n \\n <section>\\n \\n <p>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 UV<sub>254</sub> 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 (<i>k</i><sub>max</sub> = 0.021 cm<sup>2</sup>/mJ) and higher residual population density (<i>N</i><sub>res</sub> = 7.081 SFU/mL). Raw source water (<i>k</i><sub>max</sub> = 0.027 cm<sup>2</sup>/mJ, <i>N</i><sub>res</sub> = 1.168 SFU/mL, turbidity = 0.978–215 NTU) and softened water (<i>k</i><sub>max</sub> = 0.030 cm<sup>2</sup>/mJ, <i>N</i><sub>res</sub> = 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 <i>Bacillus subtilis</i> spores, <i>Cryptosporidium</i> 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.</p>\\n </section>\\n </div>\",\"PeriodicalId\":101301,\"journal\":{\"name\":\"AWWA water science\",\"volume\":\"6 6\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-12-22\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://onlinelibrary.wiley.com/doi/epdf/10.1002/aws2.70010\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"AWWA water science\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1002/aws2.70010\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"AWWA water science","FirstCategoryId":"1085","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/aws2.70010","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
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.