Section of Drinking Water Chemistry, Division of Environmental Hygiene, Hokkaido Institute of Public Health, Sapporo, Japan.
Appl Environ Microbiol. 2012 Oct;78(20):7420-8. doi: 10.1128/AEM.01502-12. Epub 2012 Aug 17.
The freshwater benthic pearl clam, Hyriopsis schlegeli, was experimentally exposed to Cryptosporidium parvum oocysts, and it was verified that the oocysts were eliminated predominantly via the fecal route, retaining their ability to infect cultured cells (HCT-8). The total fecal oocyst elimination rate was more than 90% within 5 days after exposure to the oocysts. H. schlegeli was able to survive in the final settling pond of a sewage plant for long periods, as confirmed by its pearl production. In the light of these findings, the clam was placed in the final settling pond in a trial to test its long-term efficacy in depleting oocysts contaminating the pond water. The number of clams placed was set to ensure a theoretical oocyst removal rate of around 50%, and the turbidity and the density of feed microbes in the overflow trough water of the pond were about 35% and 40 to 60% lower, respectively, than in the control water throughout the year. It was found that the clam feces containing oocysts were sufficiently heavy for them to settle to the bottom of the pond, despite the upward water flow. From these results, we concluded that efficient depletion of oocysts in the sewage water of small or midscale sewage treatment plants can be achieved by appropriate placement of H. schlegeli clams.
淡水底栖珍珠蚌（Hyriopsis schlegeli）被实验性地暴露于微小隐孢子虫卵囊下，结果证实卵囊主要通过粪便途径排出，同时保留其感染培养细胞（HCT-8）的能力。暴露于卵囊后 5 天内，粪便中的总卵囊排出率超过 90%。珍珠蚌可以在污水处理厂的最终沉淀池中长期存活，这一点从其珍珠生产中得到了证实。鉴于这些发现，将该蚌置于最终沉淀池进行试验，以检验其在长期去除污染池塘水的卵囊方面的功效。放置蚌的数量设定为确保理论上卵囊去除率约为 50%，全年在池塘溢流水槽中，浊度和饲料微生物密度分别比对照水低约 35%和 40%至 60%。结果发现，尽管存在向上的水流，含有卵囊的蚌粪便仍然足够重，可以沉降到池塘底部。根据这些结果，我们得出结论，通过适当放置淡水底栖珍珠蚌，可以有效地去除小型或中型污水处理厂污水中的卵囊。
