Comparing Chlorine Dioxide and Ozone Treatments

I am routinely asked about chlorine dioxide (CLo2) compared to ozone.  So, let me take a stab at some of the comparisons and differences that I see as someone who has used both for various jobs.

To be clear, I like chlorine dioxide.  Basically chlorine dioxide is an oxidizing treatment similar to ozone.  Chlorine dioxide and ozone carry an extra oxygen atom that drops off to attach to various targets.  Oxidation is a proven way to destroy odors, mold, and germs.  Chlorine dioxide can be placed as a tablet or powder in water so that the chlorine dioxide escapes into the room, or a more stable for is mixed in water to be fogged into areas.

Ozone is typically delivered by an ozone generator as a gas to permeate the target area.  Ozonated water cannot be effectively pushed through a fogger, but can be applied in a water spray.

If you are a big advocate of chlorine dioxide, the pitfall is that anyone who searches the internet and buy low-cost kits or supplies and do their own CLo2 treatments.  Your best bet is trying to keep your process a secret from customers who would rather cut your fees out of the budget.  

But, ozone is no secret either.  Though more expensive to purchase, an enterprising customer could figure how to cut you out of the budget and have an untrained person to the work.

Which is More Powerful?

This is a difficult question.  WHO offered a study on the best-known disinfectants.  One study is from

"By comparing the oxidation strength and oxidation capacity of different disinfectants, one can conclude that chlorine dioxide is effective at low concentrations. Chlorine dioxide is not as reactive as ozone or chlorine and it only reacts with sulphuric substances, amines and some other reactive organic substances. In comparison to chlorine and ozone, less chlorine dioxide is required to obtain an active residual disinfectant. It can also be used when a large amount of organic matter is present."

"The oxidation strength describes how strongly an oxidizer reacts with an oxidizable substance. Ozone has the highest oxidation strength and reacts with every substance that can be oxidized. Chlorine dioxide is weak, it has a lower potential than hypochlorous acid or hypobromous acid."

Read more:"

WHO offered a study on the best-known disinfectants.  

"Effectiveness of chlorine dioxide against protozoa"

"Chlorine dioxide is an effective disinfectant for control of Giardia lamblia; the required CT values for 1-log inactivation (pH 6–9) range from 5 mg min/l at 20oC to 21 mg/min l–1 at 0.5oC (USEPA, 1989b; White, 1999). The 3-log inactivation CT values (pH 6–9) range from 19 mg/min l–1 at 15oC to 63 mg/min l–1 at 0.5oC. These values are 3–14 times less than those required for free chlorine, but approximately 20 times more than those required for ozone."  

"Effectiveness of ozone against bacteria and viruses"

"Of the vegetative bacteria, Escherichiacoli is one of the most sensitive (Table3.7), while Gram-positive cocci (Staphylococcus and Streptococcus), Gram-positive bacilli (Bacillus) and mycobacteria are the most resistant (Langlais, Reckhow & Brink, 1991). Mycobacterium avium can be effectively controlled by low doses of ozone (CT99.9 of 0.1–0.2 mg/min l–1), whereas the organism is highly resistant to free chlorine (CT99.9 of 551–1552 mg/min l–1 for water-grown isolates) (Taylor et al., 2000).

CT values (mg/min l–1) for 99% inactivation at Preformed 5°C

Chlorine dioxide (pH 6–7)

Ozone (pH 6-7) 

Microorganisms tested:  E. coli, Poliovirus 1, Rotavirus, Phage f2, G. lamblia cysts, G. muris cysts