CT Disinfection Product

C T = C \cdot t ln (N / N_{0}) = - k C t

Chick–Watson: inactivation depends on concentration × time. Regulations tabulate required CT for a given log inactivation, pH, and temperature (free chlorine, ozone, UV uses fluence instead). t is contact time (often t10 from tracer).

$C$ (mg/L): Disinfectant residual
$t$ (min): Contact time
$C T$ (mg·min/L): Concentration–time product

Step-by-step solved example

C=1.2 mg/L, t=20 min. CT? If required CT=24 mg·min/L, is it enough?

CT product for a given inactivation; t is contact time.

1. Product
CT=1.2×20=24 mg·min/L.
2. Check
Equals the required 24 — just meets.

Answer: 24 mg·min/L (just meets 24)

10 practice questions

0/10 correct

1.CT is

2.Giardia typically needs

3.Baffling factor t10/T < 1 means

4.Raising C at fixed t

5.UV disinfection uses

6.Chick's law N/N0 = e^{-kt} with C folded into k is

7.Colder water generally requires

8.pH affects free-chlorine CT because

9.If t is halved you must

10.Units mg·min/L are