What is a CT Value and how is it measured?
CT Value refers to the Contact Time required for optimum disinfection. In general CT values are much lower for ozone water treatment disinfection than chlorine. Ozone essentially splits pathogens and, therefore, delivers an “instant kill”. Chlorine requires more time to penetrate the bacteria.
To claim disinfection, water treatment plants using chlorine require sufficient disinfectant concentration (C,mg/L) and contact time (T in Minutes), and effectiveness is dependent on pH and water temperature:
CT = Concentration of Disinfectant (mg/L=ppm) * Contact Time
Put more simply, the higher the concentration and the longer the contact time, the more powerful the disinfection.
A “baffle factor” is a theoretical ratio from 0.0-1.0 used to measure the true retention time of water and disinfectant, based upon the conditions of the plumbing and tanks. “Unbaffled” means there is a chance of water bypassing treatment and has a lower score; Superior baffles provide a 0.7 ratio and Perfect (plug flow”) is 1.0.
CT = Concentration of Disinfectant * Contact Time x Baffle Factor
Here is a quick CT Value calculation example with ozone:
Peak flow rate of 50gpm, applying a 10ppm dose and using a 250-gallon contact tank, means a contact time of 5 minutes. Using the 10ppm dose and the 5 minutes of contact time, we add a conservative “baffle factor” of 0.7 based on our unique system design to get a potential CT value of 35mg/ Min / L
The chart below shows the required CT Value to treat 99.99% of viruses. Chemicals require a much higher CT Value than ozone, meaning it requires a higher dose of chemicals and/or a longer period of time. This is not only inefficient it also leads to increased chemical by-products in the treated water and higher operating costs.
Ozone has the lowest minimum CT Value for the disinfection of bacteria, viruses and cysts, and therefore is most efficient. So what does this mean?
According to the CT values listed by the Health Canada website, our Aclarus Ozone systems, without filters, can achieve log-4 reduction of viruses (CT Value= 1.8, 1C), log-4 Giardia (CT Value=2.9+, 1C), and log-3 removal of Cryptosporidium at 10C (CT=30, 10C , Log-2 at 5C, Log 1.5 at 1C ).
Aclarus Ozone systems can be engineered to meet any disinfection requirement. Furthermore, they include in-line monitoring for fully automated treatment based on water quality and flow rate.