Even extremely low dosages of ultraviolet light can be highly effective for inactivating Cryptosporidium oocysts.Recent studies have shown that Cryptosporidium parvum oocysts demonstrate high susceptibility to low dosages of medium‐pressure ultraviolet (UV) light. These investigations have raised several questions, which include determination of minimum medium‐pressure UV dosages necessary to inactivate C. parvum oocysts, elucidation of differences (if any) between medium‐ and low‐pressure UV light for inactivating C. parvum oocysts, and evaluation of medium‐pressure UV effectiveness in inactivating oocysts suspended in poorer quality water. To compare low‐ and medium‐pressure UV, the authors exposed oocysts suspended in deionized water to UV delivered by either medium‐ or low‐pressure UV lamps at bench scale using a collimated beam apparatus. The applied UV dosages ranged from 3 to 33 mJ/cm2, and oocyst inactivation was assessed using the neonatal mouse infectivity assay. At 3 mJ/cm2, medium‐pressure UV showed a 3.4‐log inactivation of oocysts, and low‐pressure UV showed a 3.0‐log inactivation, demonstrating medium‐ and low‐pressure UV did not differ significantly in inactivating C. parvum oocysts.

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.

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Degradation of phenols by ozone has been extensively studied but the oxidative coupling pathway of ozone resulting in a phenol polymerization has not been largely investigated. Application of low ozone dose in solutions of 2.4 dichlorophenol and salicylic acid is characterized by the formation of high molecular compounds which are partially insoluble. Numerous polymers have been identified by gas chromatography coupled with mass spectrometry. Application of the polymerization effect of ozone to petrochemical and coking wastewaters containing phenols give similar results. In each case, phenolic compounds are efficiently removed, even if a large organic content is present. In the case of petrochemical wastewater, where phenols represent only 30% of TOC, the ozone effects are not sufficient to merit an ozonation step on the present treatment line. On the other hand, when phenols represent the greater part of the organics, as in coking wastewater, an important fraction of insoluble compounds, easily removed by filtration, are formed.