Hello everyone,

Can someone let me know how much ozone is required to oxidise 1ppm of COD?

I have well water that has to be treated to make it potable. It is first  pre-oxigenated to the point of saturation (about 5mg/L) then ozonated. The pre-oxidation will precipitate the soluble iron (1mg/L) and remove some 70% of sulfurs (2.5mg/L). The initial design of the ozone is to remove the remaining 30% of the sulfurs with a dosis of 5mg/L of ozone at 3% concentration.

However there is an unforeseen issue with the COD: we have 20mg/L and the norm is 4mg/L. So would that ozone be sufficient to reduce it to acceptable levels (<4mg/L)? The TRH of the ozone tank is 15 minutes, the water temperature is 20°C and the pH is neutral. The water also contains Mn (0.9mg/L) and Amoniac nitrogen (2.5mg/L) that will be removed through post-ozonification treatment.

Thanks in advance for your help.

Khaled

SludgeHound wrote on Oct 3^rd, 2008, 1:58pm:


I concur with this (if any validation is required).  On ozonation not involving H2S, only a single oxygen atom from the ozone molecule contributes to COD reduction.

Corb wrote on Oct 24^th, 2008, 3:30pm:


Simple questions never have simple answers.

What is in the water when you ozonate a potential host of chemicals that are blanket described as "COD"?  Lots of different things.  The key is, that biology cannot touch these compounds as "COD", but usually can as "BOD", or ozone has moved it beyond biology's interest... and then you don't usually have to worry about those.

Are the host of residual molecules that can possibly be left over after you add sufficient ozone to destroy "all" COD a problem?  Some of them are a problem for Man, but between bacteria and algae, nothing of concern is left, with some exceptions.  Bromate is one possible byproduct, and is only a legal problem if you are one of a few species of mutant rat.
http://www.ncbi.nlm.nih.gov/pubmed/18784759
There are others, and if one were to combine ozone and UV (or other advanced oxidation method), even those would be gone.

Will ozone allow you to have no knowledge of what is in any given water stream and stay out of trouble?  No, but it will do better than any "one stringed guitar" out there.  But the symphony is rarely moving with only one string.  My opinion.

If you have a particular chemical you are looking to oxidize, the International Ozone Association has published a whole series of papers on quite a few waters, and their special problems.  If you are interested in something you can either check with them, or post here.  I'll see what I can find for you.

DS wrote on Oct 27^th, 2008, 6:53am:


AOX = absorbable organic halogens

It is unusual to form AOX from bromide, COD, and ozone.  It is not unusual to form AOX from bromide, BOD, and either ozone or chlorine however.

"Biological treatment" immediately following ozonation will consume much of the AOX.  Chlorination will be a little more difficult to biologically treat afterwards, it would seem to me.