Civil Engineering - GATE Exam Questions - Discussion


The disinfection efficiency of chlorine in water treatment

[A]. is not dependent on pH value.
[B]. is increased by increased pH values.
[C]. remains constant at all pH values.
[D]. is reduced by increased pH value.

Answer: Option D


No answer description available for this question.

Anshika said: (Dec 22, 2016)  
The correct answer is D.

Annu said: (Apr 19, 2017)  
I think the correct answer is D.

Chhaya said: (Jul 11, 2017)  
Yes, correct answer is D.

Varsha Prasad said: (Oct 24, 2017)  
The right correct answer is D.

Roy said: (Nov 26, 2017)  
Yes, D is the correct answer.

Robin said: (Jan 11, 2018)  
As per my knowledge, lesser the pH value means lesser will be alkalinity so the answer is correct.

Dolly said: (May 1, 2018)  
I think Option D is correct.

Kishya Bhai said: (Mar 17, 2019)  
Cholination is not effective if the water is alkaline so option D is correct.

Swar said: (Apr 3, 2019)  
Disinfection is more efficient at low pH. So, option D should be correct.

Jay said: (Dec 27, 2020)  
A higher pH facilitates the formation of more hypochlorite ions and results in less hypochlorous acid in the water. Lower pH facilitates the formation of fewer hypochlorite ions and more of hypochlorous acid. Hypochlorous acid is the most effective form of free chlorine residual, i.e., chlorine available to kill microorganisms in the water, while hypochlorite ions are much less efficient disinfectants. So disinfection is more efficient at a low pH (with large quantities of hypochlorous acid in the water) than at a high pH (with large quantities of hypochlorite ions in the water). At a high pH, the hypochlorous acid becomes dissociated into the ineffective hypochlorite ion. So, in lower pH water disinfection will be more efficient.

Somu said: (Mar 18, 2021)  
Good explanation @Jay.

Bhagyashree Vanjare said: (Apr 4, 2021)  
Good explanation, Thanks @Jay.

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