In the chlorine contact tank example, CT stands for concentration-time.

• A. chlorine temperature
• B. concentration-time
• C. calcium test
• D. chemical transfer

Answer: (B)

CT is the product of the disinfectant concentration and the contact time. In the chlorine contact tank, water is treated with chlorine and kept in contact long enough for the chlorine to inactivate microbes. The value is calculated by multiplying the residual chlorine concentration (C) by the time the water remains in contact with it (t), typically expressed as mg/L × minutes. This CT value helps determine whether disinfection will meet the required microbial reduction: higher concentration or longer contact time increases disinfection effectiveness. The other options don’t fit because they refer to temperature, a chemical test unrelated to disinfection, or a different process altogether.