Medium‐pressure UV for oocyst inactivation

Abstract

In vivo studies indicate the infectivity of treated Cryptosporidium parvum oocysts more reliably than do in vitro assays. Inactivation of Cryptosporidium parvum oocysts in finished drinking water by medium‐pressure ultraviolet (UV) light was investigated at bench scale using a collimated beam apparatus and at demonstration scale using a UV reactor. Oocyst viability was assessed in vitro (using 4',6‐diamidino‐2‐phenylindole with propidium iodide and maximized in vitro excystation) and in vivo (using neonatal mouse infectivity assays). In vivo bench‐scale studies showed > 4‐log inactivation at UV dosages as low as 41 mJ cm–2, although in vitro surrogate assays showed little or no inactivation at this or higher UV dosages. The in vitro assays, which indicate oocyst viability, grossly overestimated the UV dosages required to prevent oocyst infection in susceptible hosts. Results of demonstration studies, carried out under the Environmental Technology Verification program of the National Sanitation Foundation and the US Environmental Protection Agency, agreed with the bench‐scale results and showed that a UV dosage as low as 19 mJ cm–2 provided 3.9‐log inactivation of Cryptosporidium oocysts.

Chlorine Dioxide Inactivation of Cryptosporidium parvum Oocysts and Bacterial Spore Indicators

“…As mentioned above, in vitro excystation was used for comparison to the results in the literature; however, excystation data were significantly different from infectivity data. As reported in other studies (4,10), our results clearly demonstrate that in vitro excystation consistently underestimates Cryptosporidium inactivation compared to infectivity assays. Oocysts capable of in vitro excystation may not necessarily be infectious, and oocysts incapable of in vitro excystation are almost certainly incapable of causing an infection.…”

Low-Pressure UV Inactivation and DNA Repair Potential of Cryptosporidium parvum Oocysts

“…Previous studies using the in vitro viability assays of excystation and vital dye staining suggested that C. parvum oocysts are also very resistant to monochromatic low-pressure (LP) UV radiation (5,21) and much more resistant than the enteric viruses that have been proposed as the basis for determining UV dosimetry in water and wastewater treatment (11,12,19). However, recent studies using in vivo animal bioassays indicate that polychromatic medium-pressure mercury lamp UV as well as LP UV extensively reduce C. parvum oocyst infectivity at relatively low doses (4,6).…”

Inactivation of MS2 Phage and Cryptosporidium parvum Oocysts Using UV-A from High-Intensity Light-Emitting Diode for Water Disinfection

“…Numerous studies have described the efficiency of UV irradiation against protozoa (Bukhari et al, 1999;Shin et al, 2001;Linden et al, 2002;Morita et al, 2002;Zimmer et al, 2003;Johnson et al, 2005), bacteria and bacterial spores (Chang et al, 1985;Sommer et al, 1998;Hijnen et al, 2006), and viruses and phages (Chang et al, 1985;Battigelli et al, 1993;Hijnen et al, 2006;Simonet and Gantzer 2006;Park et al 2011).…”