Dai X, Boll J
State Office of Technical Services, Idaho Department of Environmental Quality, Boise, ID 83706, USA.
Water Res. 2006 Mar;40(6):1321-5. doi: 10.1016/j.watres.2006.01.027. Epub 2006 Mar 3.
Understanding transport behavior of Cryptosporidium parvum oocysts and Giardia lamblia cysts (together referred to as (oo)cysts) in overland flow is important for beneficial uses of receiving water bodies. Like sediment, (oo)cysts are subjected to deposition once they are present in overland flow or low flow environments like reservoirs, wetlands and sedimentation basins. The objectives of this paper are to present the theory and experiment to determine the free settling velocity (v(s)) of (oo)cysts and to compare experimental settling velocities to estimates using Stokes' law. A settling experiment was designed to quantify the v(s) of (oo)cysts in an aqueous column. C. parvum oocysts used were spherical with average diameter (+/-1SD) of 6.6+/-1.1 microm. G. lamblia cysts were oval shaped (average eccentricity = 1.48+/-0.19) with average size of 11.8 +/-1.3 microm. Average densities were 1009 kg m(-3) for C. parvum oocysts and 1013 kg m(-3) for G. lamblia cysts. Observed experimental settling velocities are 0.27 microm s(-1) and 0.67 microm s(-1) for C. parvum and G. lamblia, respectively. Estimated average settling velocities using Stokes' law were 0.36 microm s(-1) for C. parvum and 0.84 microm s(-1) for G. lamblia. R-squared values of the observations from the settling experiments with the Stokes' law estimation are 0.87 and 0.88 for G. lamblia and C. parvum, respectively. Our results suggest that Stokes' law can be used to estimate settling velocities of (oo)cysts. Qualitatively, the low settling velocities indicate that (oo)cysts will very slowly settle out of suspension.
了解微小隐孢子虫卵囊和蓝氏贾第鞭毛虫包囊（统称为（卵）囊）在地表径流中的输运行为对于受纳水体的有益利用至关重要。与沉积物一样，（卵）囊一旦存在于地表径流或水库、湿地和沉淀池等低流量环境中，就会发生沉积。本文的目的是介绍确定（卵）囊自由沉降速度（v(s)）的理论和实验，并将实验沉降速度与使用斯托克斯定律的估计值进行比较。设计了一个沉降实验来量化（卵）囊在水柱中的v(s)。所用的微小隐孢子虫卵囊呈球形，平均直径（±1SD）为6.6±1.1微米。蓝氏贾第鞭毛虫包囊呈椭圆形（平均偏心率 = 1.48±0.19），平均大小为11.8±1.3微米。微小隐孢子虫卵囊的平均密度为1009千克/立方米，蓝氏贾第鞭毛虫包囊的平均密度为1013千克/立方米。微小隐孢子虫和蓝氏贾第鞭毛虫的实验观测沉降速度分别为0.27微米/秒和0.67微米/秒。使用斯托克斯定律估计的微小隐孢子虫平均沉降速度为0.36微米/秒，蓝氏贾第鞭毛虫为0.84微米/秒。蓝氏贾第鞭毛虫和微小隐孢子虫沉降实验观测值与斯托克斯定律估计值的决定系数（R平方）分别为0.87和0.88。我们的结果表明，斯托克斯定律可用于估计（卵）囊的沉降速度。定性地说，低沉降速度表明（卵）囊将非常缓慢地从悬浮液中沉降出来。
