Nr.6014-Review on Chlorine Dioxide as a Disinfectant

Dr. Mrinal Kanti Ghosh

Review on Chlorine Dioxide as a Disinfectant

The disinfection capabilities of ClO₂ were recognized in the 1940s not long after its introduction in water treatment (McCarthy, 1944). White (1972) mentioned several early studies in which ClO₂ was an effective bactericide over a broad range of pH values (Ridenour and Ingols, 1947) and an effective virucide (Hettche and Ehlbeck, 1953). White (1972) also reported on the work of Bernarde et al. (1965), who found that the disinfection efficiency of ClO₂ increases as a function of pH. Lykins et al. (1991) summarized CT (concentration times contact time) data from several more recent disinfection studies (Hoff, 1986; Federal Register, 1989; Korich et al., 1990) that show ClO₂ to be a superior disinfectant to free chlorine and chloramines against Giardia lamblia, Giardia muris, and Cryptosporidium parvum. The CT value for  Cryptosporidium inactivation by ClO₂ is three orders of magnitude less than the CT values for inactivation by free chlorine and chloramines at pH 7 and 25°C (CT of 78 for 90 percent inactivation for ClO₂, 7200 for 90 percent inactivation for chloramines, and 7200 for 99.9 percent inactivation for free chlorine). Finch et al. (1995) reported the CT value for 99.9 percent Cryptosporidium inactivation with ClO₂ was 140 (pH 7 and 25°C) using animal infectivity data. Liyanage et al. (1997) reported a synergistic effect on Cryptosporidium parvum inactivation when ClO₂ pretreatment was followed by application of free chlorine or monochloramine. They found that ClO₂ (1.3 mg/L for 120 minutes) followed by free chlorine (1.6 mg/L for 120 minutes) resulted in a 3 log-unit (99.9 percent) reduction in infectivity. Similarly, they found that ClO₂ (1.5 mg/L for 120 minutes) followed by monochloramine (2.8 mg/L for 180 minutes) resulted in a 2.8 log-unit (99.84 percent) reduction in infectivity. The expected inactivations by ClO₂, free chlorine or monochloramine alone were 1.7 (98 percent), 0.0, and 0.0 log-units, respectively. The researchers hypothesized that the synergistic effect demonstrated by sequential disinfection is because “the stronger oxidant conditions the outer membrane of the oocysts so that the secondary oxidant can penetrate the oocyst wall more readily.”

Chlorine dioxide is a powerful disinfectant. In fact, most research has determined that it is either more effective or equal to chlorine on a mass-dose basis (Rittman 1997). In regards to bacterial inactivation, Trakhtman (1949) determined that ClO₂ doses of 1 mg/L to 5 mg/L were sufficient to kill Escherichia coli and Bacillus anthracoides in turbid waters. Bedulivich et al. (1954) showed that ClO₂ was equal to or better than chlorine in effectiveness against Salmonella typhosa and S. paratyphi.

Similar studies have shown ClO₂ to be an effective disinfectant against other bacteria of concern,including Eberthella typhosa, Shigella dysenteriae, S. paratyphi B, Pseudomonas aeruginosa, and Staphylococcus aureus (Ridenour 1949).

As well as being an effective bactericide, ClO₂ has also been shown to be effective for inactivation of many viruses. Various researchers have proven its effectiveness against Poliovirus 1 and Coxsackie virus A9 (USEPA 1999 citing Ridenour and Ingols 1946, Cronier et al. 1978, and Scarpino 1979). When compared to chlorine at 8 higher than neutral pH, ClO₂ is a stronger disinfectant against Echovirus 7, Coxsackie virus B3, and Sendaivirus (Smith and McVey 1973). Of great concern to water utilities today are the pathogenic protozoa Giardia lamblia, Giardia muris, and Cryptosporidium parvum. Researchers have found that Giardia cysts and Cryptosporidium oocysts are largely resistant to free chlorine, UV irradiation, and chloramines (Korich et al. 1990; Lorenzo-Lorenzo et al. 1993; Ransome et al. 1993). Hofmann et al. (1997) showed a 3-log Giardia inactivation after a 60-minute contact time with ClO₂ at dosages between 1.5 mg/L and 2 mg/L. Lykins et al.(1991) showed that ClO₂ is also a strong disinfectant against Cryptosporidium oocysts.

*Comparison With Other Disinfectants is done by comparison test - concentration required for a > 10⁵ reduction in viable cell  counts in 60 secounds.

* Journal of Industrial Microbiology, 4 (1989) 145 - 154, Ralph S. Tanner

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