The effect of temperature on the efficacy of ozonation for inactivating Cryptosporidium parvum oocysts

Abstract

Examination of the effects of water temperature on the inactivation of Cryptosporidium parvum oocysts with ozone, ozonation experiments were conducted in a semi-batch mode with a wide temperature range of 3-30 degrees C. Inactivation was assessed in terms of mice infectivity and in vitro excystation. The temperature dependency of the CT products by a reduction in infectivity of 2 log10 could be described successfully by the Arrhenius equation, 1/CT = 1.086 x 10(18)e-12520/K where CT is the integrated ozone concentration over the contact time (mg/min/L) and K is the Kelvin temperature of water. As for the reduction in viability assessed by the excystation assay, protocol B, the obtained regression equation, 1/CT = 1.802 x 10(18)e-12640/K, was almost identical to that observed for the infectivity. Thus, the CT products required for a 2 log10 reduction in both infectivity and viability increased by an average factor of 4.2 for every 10 degrees C decrease in water temperature. Additionally, our findings suggested that the viability, as determined by protocol B, could substitute for animal infectivity in evaluating the effects of environmental factors on the efficacy of ozonation.

Efficacy of UV Irradiation in Inactivating Cryptosporidium parvum Oocysts

“…The estimated UV dose for a 2-log 10 reduction in viability at 20°C was 230 mWs/cm 2 , which is approximately 200 times higher than the dose required for an equivalent reduction in infectivity. Hirata et al reported that the CT (product of concentration of disinfectant and contact time) values of chemical disinfectants required for equivalent reductions in the infectivity and the viability of C. parvum differed by a factor of 18 for chlorine (12) and by a factor of 3 for ozone (13). The present study showed a marked difference between the effect of UV irradiation on the infectivity of C. …”

“…The CT requirement of chemical disinfectants generally depends on both the temperature and the concentration of the disinfectant (5, 13). For instance, the temperature factor of ozone has been reported to be as high as 4.09 (16) or 4.20 (13) for every 10°C reduction in temperature. However, temperature did not significantly affect the efficacy of UV irradiation in reducing the infectivity of oocysts in this study.…”

Depletion of Cryptosporidium parvum Oocysts from Contaminated Sewage by Using Freshwater Benthic Pearl Clams (Hyriopsis schlegeli)

“…In order to determine whether C. parvum oocysts are digested by H. schlegeli clams, or whether they remain infectious after ingestion in vitro, qualitative detection of C. parvum oocysts obtained from clam feces was carried out using cultured human colon tumor (HCT-8) cells, as reported elsewhere (19,45,48) and described briefly below.…”

The efficiency of ozonated water from a water treatment plant to inactivate Cryptosporidium oocysts during two seasonal temperatures

“…The supernatant was aspirated and the pellet was resuspended in 100 ml PBS (pH 7.4). A pre-incubation procedure was performed by mixing the sample with acidified Hank's balanced salt solution (HBSS) and incubated at 378C for 30 min (Hirata et al 2001). The washed pellet was resuspended in 100 ml of PBS and 10 ml of 1% (w/v) sodium deoxycholate in Hank's minimal essential medium and mixed with 10 ml of 2.2% (w/v) NaHCO 3 in HBSS.…”

“…The washed pellet was resuspended in 100 ml of PBS and 10 ml of 1% (w/v) sodium deoxycholate in Hank's minimal essential medium and mixed with 10 ml of 2.2% (w/v) NaHCO 3 in HBSS. The samples were incubated at 378C for 4 h as described previously (Robertson et al 1993;Vesey et al 1997;Hirata et al 2001). When the excystation protocol was completed, 25 ml of sample was air-dried onto Spot-on-slides Mean excystation of ozonated water sample Mean excystation of filtered water sample from WTP £ 100…”