Lets try again. Remember that the water is being pumped from an anaerobic well. As soon as the water is exposed to air, the oxidation of iron will initiated.

Oxygen is dissolved (rather than entrained) in the aerator. The splashing and cascading effect in the aerator will thoroughly mix the water and oxygen prior to the water entering the detention tank. Think of the aerator as being a rapid mix tank with oxygen being added.

Sometimes, a clarifier instead of a detention tank is situated underneath the aerator. If you are using a clarifier in that application, you would not want any mixing in the clarifier.

Theoretically, 1 mg/l of DO will oxidize 7 mg/l of iron. The solubility of oxygen from air dissolved in water is about 7 ml per liter at 59 Deg F, which is about 10 mg/l.  So you can see that water saturated with dissolved air at about 60 Deg F contains enough oxygen to oxidize some 70mg/l of iron.

This oxidation is very slow at low pH values and rapid at high pH values. At a pH of 5, only about 1/10 the iron will be oxidized in 15 minutes. At a pH of 6, 1/2 of the iron will be oxidized in 15 minutes. At a pH of 7 and above, essentially all of the iron will be oxidized within 15 minutes.

In summary, you have an excess of oxygen added in the aerator and mixing is not critical because the reaction occurs rapidly.


http://www.eng-tips.com/viewthread.cfm?qid=106305

Thanks bimr.
Interesting thread link you posted.  One thing, the well water never breaks pressure before hitting the sediment filter so aeration is not an option (at least not for this owner).  

Any theoretical ? mg/l of chlorine to oxidize 1 mg/l of Fe?

Sorry, I thought it was on there.

1 mg/l of chlorine will oxidize about 1.6 mg/l of ferrous iron, expressad as Fe in both instances. However, with chlorine it is possible to oxidize the iron rapidly at a lower pH than with oxygen.