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Name: Louis
Status: Other
Grade:  Other
Location: CO
Country: United States
Date: Winter 2009 - 2010


Question:
Since bacteria which are pathogenic to humans are adapted to pH levels of about 7.4, what pH levels might be sufficient deactivate or kill these pathogens ? For instance if infected drinking water is given a reduced pH, how low would the pH have to be in order to kill human pathogens ? How long would this pH have to be sustained for it to be effective in killing the pathogens ? Conversely, how high above 7.4 pH would the pH have to be to kill these pathogens ? And for how long?



Replies:
I'm guessing that the pH would have to be plus or minus 2 pH units from the optimum pH. This would not be a practical way of controlling the bacterial population.

Ron Baker, Ph.D.


You make some extraordinary leaps of faith. Since bacteria which are pathogenic to humans are adapted to pH levels of about 7.4. This an assertion. Is it supported by experimental data?

"Since bacteria which are pathogenic to humans are adapted to pH levels of about 7.4, what pH levels might be sufficient deactivate or kill these pathogens ?

You have to be careful about what is "chemically" and/or "biologically" acceptable but is not but not acceptable from a utilitarian perspective. This gets into other issues than "chemistry".

But having raised the issue, a discussion is worth the positive and negative values are worth discussion.

Vince Calder


Extreme pH can be used to kill bacteria, but every organism is different. Some bacteria are highly resistant to acids or bases, while others are less resistant. Some bacteria are very happy in very low pH, while others prefer high pH -- so there's no "general rule" for how long or what pH to kill bacteria.

Also, the chemicals you would need to add to drastically change the pH would typically render the water unsuitable for drinking. So generally pH is not used to sterilize water for this reason.

Hope this helps,
Burr


Yeah, E-Coli definitely gets killed by high pH -- and others get killed by low pH too. We used caustic/sulfamic alternations in industry to help sterilize our fermentation tanks. But there you rinse the tank clean and empty it. That wasn't the question asked though. I thought the student was asking about water purification -- dumping in caustic or acid into drinking water wouldn't work. And, drinking water purification is much more than bacteria... spores, fungi, etc. etc. (I can get that article for you if you want, by the way.)

Burr



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