Chlorine CT & Contact Tank
Calculate nominal detention time, effective contact time and achieved CT.
Calculator inputs
Results
Equations and method
Nominal time = V/Q. Effective time T10 = factor × V/Q. Achieved CT = measured residual × T10. Required volume = required CT × Q ÷ (residual × factor).
Worked example
At 500 gpm, 10,000 gal, a 0.5 contact factor and 1 mg/L residual: nominal time = 20 min, T10 = 10 min and CT = 10 mg·min/L.
Scope and assumptions
Use operating water volume and peak flow. The contact factor must reflect tracer results or an accepted estimate. Required CT depends on disinfectant, organism, temperature, pH and treatment goal; enter an applicable value. The example target is illustrative. The ratio shown is a numerical comparison, not a regulatory compliance determination.
Related water-treatment calculators
Equation values and input guide
Enter peak flow, operating water volume and a defensible effective-contact factor. Use the measured outlet residual and a required CT appropriate to your treatment conditions; the tool does not select that target.
- V, Q
- Operating water volume and flow rate in compatible volume/minute units for V/Q.
- Nominal time, T10
- Ideal volume/flow detention time and effective contact time, in minutes. T10 uses the entered factor to account for short circuiting.
- Contact factor
- Dimensionless T10/(V/Q), obtained from tracer data or an accepted estimate for the basin.
- C, CT
- Measured disinfectant residual in mg/L and residual times effective time in mg·min/L. CT is a concentration-time product, not a dose.
- Required CT, required volume
- A user-supplied treatment target and the calculated volume needed at the entered flow, residual and contact factor. Those conditions must remain valid for the volume estimate.
Use the unit selectors beside the inputs. Units shown in the equations must be consistent when checking the math by hand.