Settling characteristics of Cryptosporidium and Giardia under different environmental conditions.

摘要

The protozoa parasites Cryptosporidium sp. and Giardia lamblia have been implicated as the causative agents of many outbreaks of waterborne intestinal illness. The literature review results indicated that Cryptosporidium and Giardia are commonly detected over a wide range of concentrations in a wide variety of aquatic systems. Water appears to be an important vehicle for transmission of these parasites, along with direct contact with contaminated fecal material or by ingestion of contaminated food or water. Sedimentation was identified as an important mechanism that reduces the concentration of Cryptosporidium and Giardia in lake and reservoir.; Recent investigations do not include settling characteristics of these pathogens in lakes and reservoirs. The present work is trying to address this important issue. Research and experimental analysis of settling velocity of Cryptosporidium and Giardia was done in a laboratory set up. The experimental set up was designed for a column study using filtered tap water with only protozoa in the media.; The Particle Image Velocity (PIV) was used to measure settling velocity of these particles under different environmental conditions. This is the first time that PIV was used to measure the settling velocity of Cryptosporidium and Giardia. PIV contains, PIV CAM 10-30 digital camera, synchronizer, laser head and argon laser power supplies. The results were compared with mathematical description of their sedimentation velocity by using Stokes' Law. In addition size and density of Cryptosporidium and Giardia were measured. Results obtained clearly identified that their settling velocities are unique and depend on density and diameter of them. Additionally the effect of temperature and activity was investigated and proved to be an important factor. For both Cryptosporidium and Giardia, alive or dead, the settling velocity increased as temperature increased. Furthermore in warmer temperature the settling velocity of inactive (oo)cysts increase.