CT Value for Disinfection

\[CT=C\cdot T\]

Variables

CTdisinfection CT value (mg·min/L)

Cresresidual disinfectant concentration (mg/L)

Tcontacteffective contact time (min)

Description

What is this formula?

This formula calculates the CT value for disinfection by multiplying the residual disinfectant concentration by the effective contact time.

When to use it

Use it when evaluating chlorination, ozone, chlorine dioxide, or other disinfectant systems in drinking water and wastewater treatment.

Example

Data:

Cres = 1.5 mg/L

Tcontact = 30 min

Formula:

CT = Cres × Tcontact

Substitution:

CT = 1.5 × 30

Result:

CT = 45 mg·min/L

Applications

Drinking water disinfection, wastewater disinfection, chlorination design, regulatory compliance, pathogen inactivation, Giardia control, virus control, and treatment plant operation.

Note

CT is a practical disinfection indicator. Required CT values depend on disinfectant type, target organism, temperature, pH, disinfectant residual, and required log inactivation. Regulatory tables often provide minimum CT values for specific conditions.