Question

Fecal Coliform (FC) concentration in river water was measured as 10708 cfu/100 ml. The FC concentration after the conventional water treatment, but before chlorination, was measured as 23 cfu/100 ml. The 'Log Kill' (inactivation) of FC due to the conventional water treatment is closest to:

• A. 4.00
• B. 2.50
• C. 2.67
• D. 3.00

Hint:

The Log Kill value is useful in measuring the effectiveness of water treatment processes in eliminating harmful microorganisms. A higher Log Kill value indicates more effective disinfection.

Answer 1

The Correct Option is C

The 'Log Kill' is defined as the logarithmic reduction in the concentration of microorganisms after a treatment. It is given by the formula:

\[ \text{Log Kill} = \log N_0 - \log N_t, \]

where:

• \( N_0 \) is the initial concentration (before treatment),
• \( N_t \) is the final concentration (after treatment).

Given:

• \( N_0 = 10708 \, \text{cfu/100 ml} \),
• \( N_t = 23 \, \text{cfu/100 ml}. \)

Substituting these values into the formula:

\[ \text{Log Kill} = \log 10708 - \log 23 = 4.029 - 1.361 = 2.667. \]

Thus, the Log Kill is approximately 2.67. The correct answer is option (C).