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pH and Pathogens
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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