QUESTION - Re: Ozonation and HPC/Coliform Bacteria

max at gte.net max at gte.net
Mon Mar 18 18:28:42 EST 1996

Robert <zippy at mlode.com> wrote:
>I manage a domestic water treatment facility with ozonation as the first
>step in the treatment process. The raw water source is of good bacterial
>quality, i.e., fecal coliform 20-40/100ml, often less. The ozone contact
>basin is designed to provide adequate contact time and ozone residual
>for disinfection of the raw water. However, we get heterotrophic, total
>coliform and fecal coliform counts in our ozone residual water sample
>lines. My question is: how effective is ozonation, in dosages of 0.4-0.6
>mg/L for several minutes, in the inactivation of the aformentioned
>bacteria? Should we not expect a total kill-off of these organism with
>ozone. In my past experience pre-chlorination has reduced the counts to
>nil. Thank you!

You should get total kill at that level of ozone.  Your contact time should be a min 
of 5 minutes though, that may be your problem.  And FYI, I don't feel that 20-40 cfus 
of fecal coliform/100mL is water of good bacterial quality.  It is possible that your 
bacteria load is too high to get 100% kill.  With the chlorination you may not have 
been getting total kill, when testing the water you may have had stressed organisms 
that did not grow right away, and did you dechlorinate the samples that you plated??


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