Recommended Treatment Levels of Ozone For Particular Microbial Species
There is a two-step procedure for determining the recommended treatment levels of ozone. First, the grams of ozone that you need to produce to oxidize the grams of contaminants. The second is the disinfection calculation, measured in mg/l of ozone over a specific period. Inactivating a living organism requires concentration and time (Ct).
Ozone CT Values for Microorganism Inactivation
| Organism | Concentration (ppm) | Minutes | CT |
|---|---|---|---|
| Algae (blue-green) | 0.3 | 5.0 | 1.5 |
| Bacteria (all species), recommended | 0.1 | 1.0 | 0.1 |
| Escherichia coli (E. coli) | 0.04 | 1.0 | 0.04 |
| coliphage MS2 | 0.2 | 0.5 | 0.1 |
| Heterotrophic Bacteria HPC | 0.2 | 0.5 | 0.1 |
| Mycobacterium tuberculosis, leprae | 0.01 | 6.0 | 0.06 |
| Pseudomonas aeruginosa, fluorescens | 0.01 | 0.1 | 0.01 |
| Salmonella, all | 0.01 | 0.1 | 0.01 |
| Staphylococcus, sp, albus, aureus | 0.01 | 0.1 | 0.01 |
| Streptococcus, all | 0.01 | 2.0 | 0.02 |
| Fungus, Mold, Yeasts | 0.3 | 5.0 | 1.5 |
| Nematodes, all, recommended | 1.0 | 5.0 | 5.0 |
| Protozoa, all, recommended | 1.5 | 5.0 | 7.5 |
| Acanthamoeba & Naegleria | 0.2 | 0.5 | 0.1 |
| Amoeboe Trophozoites cysts | 0.4 | 4.0 | 1.6 |
| Cryptosporidium, recommended | 1.5 | 5.0 | 7.5 |
Information written for the Drinking Water Unit of EPA’s Region 10 by Jim Eagleton.
Note
The CT factor is the product of the ozone concentration (ppm) and the contact time (minutes). Essentially, the higher the CT factor, the more difficult it is to kill the organism.
The CT value (Concentration × Time) represents the relationship between dissolved ozone concentration and contact time required for effective microorganism inactivation. Because CT is linear, the same disinfection effect can often be achieved either with a lower ozone concentration and a longer contact time or with a higher ozone concentration and a shorter contact time. For example, a microorganism requiring a CT value of 0.01 may be inactivated with 0.01 mg/L of ozone for 1 minute, 0.1 mg/L for 0.1 minutes, or 1.0 mg/L for 0.01 minutes (0.6 seconds), as long as the product of concentration and time remains constant.