Dection Method And Risk Assessment For Giardia And Cryptosporidium In Drinking Sourece Water

Giardia and Cryptosporidium are common protozoan parasites that infest the gastrointestinal tract of humans and animals. These parasites have caused many waterborne outbreaks which affected hundreds of thousands of people, and consequently raised public concerns worldwide. The detection method for Giardia and Cryptosporidium includes four steps: filtration, purification, dying and microscopic examination. The filtration is a key step but there are some shortcomings such as amounts of work, high cost, etc. This paper explored a new detection method of precipitation by calcium carbonate and density-gradient centrifugal purification. By investigating and detecting the raw water of drinking water plant form an open river, the health risk is envaluated. The main results are summarized as follows:(1) The method of calcium carbonate precipitation is efficient to concentrate the Cryptosporidium cysts and Giardia oocysts in drinking source water. The number of cysts and oocysts were detected in the liquid and precipitate. In the liquid, the average detection rate of cysts and oocysts were1.2%and1.1%, individually; The concentration efficiency was higher than98%. The results show that calcium carbonate precipitation method can efficiently remove the cysts and oocysts from source water into precipitate.(2) Based on the pretreatment of calcium carbonate precipitation, the methods of Percoll-sucrose density-gradient seperation (PSDGS) and IMS were focused. The mean recovery rates of PSDGS and IMS were individually72.3%and59.1%for cysts and they were39.5%and52.2%for oocysts, respectively. All the data meet the definitive range of EPA. PSDGS was more fit to detect the cysts and very economical.(3) The source water of drinking water plant form an open river was detected by the calcium carbonate precipitation and PSDGS purification and the numbers of cycts and oocysts were0-4and0-13oocysts in10L source water, respectively. By the dosage-efficiency model, the health risk for oocysts was evaluated. The risk values of effluent from the normal treatment process and senior treatment process were individually3.71X10-6and3.71X10’8, which was far lower than of the highest risk value of10-4for America. This shows that the effuent is safe for the treatment process at present operating conditions.