Academic journal article Journal of Environmental Health

Shedding UV Light on the Cryptosporidium Threat

Academic journal article Journal of Environmental Health

Shedding UV Light on the Cryptosporidium Threat

Article excerpt

Abstract Protecting the public from waterborne outbreaks of cryptosporidiosis requires barriers beyond those provided by filtration. While sequential chemical disinfection has shown promise, concern over disinfection by-products may limit its use. This paper re-examines past evaluations of the effect ultraviolet light has on Cryptosporidium oocysts and reviews recently generated data on the topic. The studies demonstrate that ultraviolet light could have promising effects on Cryptosporidium in drinking-water applications.

Editor's note: Through NEHA's long-standing and excellent relationship with NSF International, NEHA was granted permission by NSF International to share with the Journal's readership various papers that were presented January 12-15, 2000, at the "NSF International Small Drinking Water and Wastewater Systems International Symposium and Technology Expo" in Phoenix, Arizona. This paper "Shedding UV Light on the Cryptosporidium Threat," is one of them.

It is important to note that these papers were screened by an NSF International advisory committee prior to their presentation at the conference, but they have not been peer reviewed by NEHA's Journal program for technical accuracy.

Because these papers contain useful and interesting ideas and information that may be either delayed or lost if the papers were sent through the Journal's normal peer review process, NEHA has decided to publish them as presented, with only minor editorial modifications.

We hope you look forward to more of these papers in future issues of the Journal!

Cryptosporidium Control Through Water Treatment

The public health effects of waterborne Cryptosporidium oocysts are well recognized. As a response to this health threat, significant public policy changes have been made to regulate and control the presence of this pathogen in drinking-water supplies. Like Giardia, Cryptosporidium oocysts can be controlled by physical removal through filtration processes, although oocyst removals can be expected to be lower than for Giardia, because of their smaller size. Cryptosporidium removal has been assessed with a variety of treatment techniques, and removals range from 2 to 4 log in conventional systems (Ongerth and Pecoraro, 1995; Nieminski and Ongerth, 1995; Plummer et al., 1995; Hall et al., 1995). Diatomaceous earth filtration was shown to provide 3.8- to 6-log oocyst removal in bench-scale studies (Ongerth and Hutton, 1997). Membrane processes (ultrafiltration and microfiltration) have been shown to provide high levels (greater than 6 log) of oocyst removal (Jacangelo et al., 1995).

Unlike Giardia, however, Cryptosporidium oocysts that escape the filtration process are resistant to chlorine-based disinfectants at the concentrations and contact times practical for water treatment (Korich et al., 1990). This makes the physical removal process (coagulation, sedimentation, filtration) the most critical step in conventional water treatment in plants using chlorine for disinfection. Alternative disinfectants do exist.

Ozone is highly effective for Cryptosporidium control. Korich et al. (1990) demonstrated that exposure to ozone at 1 milligram per liter (mg/L) reduced oocyst viability from 84 percent to 0 percent after five minutes at 35[degrees] Exposure times of five and 10 minutes resulted in 90 percent to 99.9 percent reduction in neonatal mouse infectivity. These data are further supported by Finch et al (1993), who also used ozone to treat oocysts and found it to be highly effective for oocyst inactivation. Further work by Finch et al. (1997) has shown that a synergistic effect occurs with combinations of certain disinfectants, with a higher-log inactivation of oocysts occurring when the chemicals are applied sequentially than when each one is used individually. For example, an initial residual of 2.0 mg/L chlorine for 240 minutes resulted in a 0.4-log inactivation of Cryptosporidium; an ozone dose with an initial residual of 0. …

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