Chlorine is used as the disinfectant in a municipal water treatment pl...
Introduction:
In a municipal water treatment plant, chlorine is commonly used as a disinfectant to kill microorganisms and make the water safe for consumption. The efficiency of chlorine in killing microorganisms is measured in terms of disinfection efficiency. In this question, we are given that chlorine achieves 50 percent disinfection efficiency in 3 minutes. We need to determine the minimum time required to achieve 99 percent disinfection efficiency.
Calculation:
To calculate the minimum time required to achieve 99 percent disinfection efficiency, we can use the concept of microbial reduction. The microbial reduction is a measure of the logarithmic reduction in the number of microorganisms. It can be calculated using the following formula:
Microbial reduction = log(N₀/N)
Where:
- N₀ is the initial number of microorganisms
- N is the number of microorganisms after a certain time
In this case, we are given that chlorine achieves 50 percent disinfection efficiency in 3 minutes. This means that after 3 minutes, the number of indicator microorganisms (E-Coli) is reduced to 50 percent of its initial value. Therefore, we can say that N/N₀ = 0.5.
To calculate the minimum time required to achieve 99 percent disinfection efficiency, we need to find the time at which N/N₀ = 0.01 (99 percent reduction). Let's assume this time as 't':
0.01 = log(N₀/N)
0.01 = log(N₀/(N₀/2))
0.01 = log(2)
0.01 = 0.301
Therefore, t = 0.301.
This means that the time required to achieve 99 percent disinfection efficiency is approximately 0.301 times the time required to achieve 50 percent disinfection efficiency.
Given that the time required to achieve 50 percent disinfection efficiency is 3 minutes, we can calculate the minimum time required to achieve 99 percent disinfection efficiency as follows:
t = 0.301 * 3
t ≈ 0.903 minutes
Converting minutes to seconds, we get:
t ≈ 0.903 * 60 ≈ 54.18 seconds
Therefore, the minimum time required to achieve 99 percent disinfection efficiency is approximately 54.18 seconds, which can be rounded off to 55 seconds. The closest option to this value is 19.93 minutes (option D).
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