Fecal Coliform (FC) concentration in river water was measured as 10780 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
Calculating Fecal Coliform Log Kill
The 'Log Kill' represents the logarithm (base 10) of the ratio between the initial concentration and the final concentration of a contaminant, indicating the level of inactivation achieved.
Log Kill Formula
The formula used to calculate Log Kill is:
$ \text{Log Kill} = \log_{10} \left( \frac{\text{Initial Concentration}}{\text{Final Concentration}} \right) $
Applying the Formula
Given:
- Initial Fecal Coliform (FC) concentration = 10780 cfu/100 ml
- Final FC concentration (after treatment) = 23 cfu/100 ml
Substitute these values into the Log Kill formula:
$ \text{Log Kill} = \log_{10} \left( \frac{10780 \text{ cfu/100 ml}}{23 \text{ cfu/100 ml}} \right) $
Calculation Steps
- Calculate the ratio of initial to final concentration:
$ \frac{10780}{23} \approx 468.7 $
- Calculate the base-10 logarithm of the ratio:
$ \log_{10}(468.7) \approx 2.6708 $
- Round the result to the nearest appropriate value based on the options.
The calculated Log Kill is approximately 2.67.
Result Interpretation
The Log Kill of 2.67 indicates that the conventional water treatment process inactivated Fecal Coliform bacteria by a factor of approximately $10^{2.67}$, which is around 468 times the original count.
Important Questions from Disinfection
The dose of chlorination, beyond which any further addition of chlorine will appear as free residual chlorine, is known as:
A city that has a supply of 15000 cubic meters of water per day is treated with a chlorine dosage of 0.5 ppm. For this purpose, the requirement of 25% bleaching powder per day would be.
Which one of the following is used to kill the pathogens?
An experiment shows that a concentration of 0.1 g/m3 of free available chlorine yield a 99% kill of bacteria in 8 minutes. Calculate disinfection rate constant (1 /min)? Assume that Chick's Law and Watson's Law hold with n = 1.
Order 4 disinfectants in increasing order of their disinfection power?
