Disinfection CT Calculator
One milligram per litre of chlorine held for 30 minutes (CT = 30) with k = 0.15 gives 1.95433 log of inactivation, about 98.9 %.
1.95432516856463 log
Full answer, then cut to fewer decimals (not rounded):
- 1.95432516856463 log
- 1.9543251685646 log
- 1.954325168564 log
- 1.95432516856 log
- 1.9543251685 log
- 1.954325168 log
- 1.95432516 log
- 1.9543251 log
- 1.954325 log
- 1.95432 log
- 1.9543 log
- 1.954 log
- 1.95 log
- 1.9 log
- CT value C × t
- 30 mg·min/L
- Surviving organisms N
- 11108.99654 per 100 mL
- Inactivation
- 98.88910035 %
Step-by-step solution
- ln(N/N₀) = −k Cⁿ t = −0.15 × 1^1 × 30 = −4.5
- log removal = 4.5 ÷ 2.303 = 1.954325169
- N = N₀ e^(−4.5) = 11108.99654
Disinfection CT Formula
ln(N/N₀) = −k Cⁿ t
CT = C × t (mg·min/L); log removal = k Cⁿ t ÷ 2.303
Worked Example
1 mg/L of chlorine for 30 minutes with k = 0.15 L/(mg·min):
- ln(N/N₀) = −k Cⁿ t = −0.15 × 1^1 × 30 = −4.5
- log removal = 4.5 ÷ 2.303 = 1.954325169
- N = N₀ e^(−4.5) = 11108.99654
Surviving organisms N: 11108.99654 per 100 mL · Inactivation: 98.88910035 %
GATE tip
Chick’s law is first-order decay in organisms: N = N₀e^(−kt). Combined with a reactor model, a CSTR contact tank gives far less kill than a baffled plug-flow tank of the same volume.
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Frequently asked questions
What does the dilution coefficient n mean?
n = 1 means concentration and time are interchangeable (same CT, same kill); n > 1 means concentration matters more than time.
How are CT targets set?
Regulators tabulate CT values for each log removal of Giardia and viruses by disinfectant, temperature and pH; operators keep actual CT above them.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
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APA
Scientific Converters. (2026, October 15). Disinfection CT Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/disinfection-ct-calculator/
IEEE
Scientific Converters, "Disinfection CT Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/disinfection-ct-calculator/