Redox potential and anaerobic condition

[wooden_reefer]

A few articles I read state that at a Redox Potential Eh of about 200-250 mv, denitritfication can become active when other conditions are correct. Then almost invariably they relate such Eh with oxygen level, specifically a rather low oxygen level.

First, do you think that in the aquarium the only way to achieve a Eh of 200-250 MV is by depleting O2? I believe Eh is basically an electrochemical concept, not necessarily just about oxygen. Authors invariably relate this range of Eh with anaerobic condition or oxygen level. Is this presumptive?

Second, I think about the relationship between stagnation of water in small space and anaerobic condition. People often equate the two. Stagnant water can be saturated with oxygen. There must be some processes, biological or not, that deplete the small amount of possibly once saturated oxygen even in stagnant water, in order for the oxygen to be depleted.

In the denitrification coil, there is the nitrification section at the intake part of the coil; it is explained that it is by aerobic nitrification that the O2 is consumed; thus a more anaerobic condition exists in the rear end of the coil, so denitrification can take place.

The reason I ask is that may be when nitrification and denitrification occur in close proximity is when denitrification can best take place, since nitrification depletes the oxygen. (There must be numerous random denitrification coils.)

However, nitrification can be one of many bacterial or physical processes that consume oxygen, so I cannot be sure if nitrification is even the predominant means of depleting oxygen.

 

[wooden_reefer]

Is nitrification the predominant way O2 is depleted in the substrate or filter medium?

The explanation of how the denitrification coil works suggests so. I have doubts that nitrification is the predominant aerobic bacterial activity in the filiter medium, however.

Do nitrification and denitrification occur in close spatial proximity? If nitrification is the predominant way oxygen is consumed in the medium or substrate, then I would tend to think so.

The question is whether there should be separate sections for nitrification and denitrification or is it better that the medium has micro-sections within itself. This may be why LR seems to have a better balance between nitrification and denitrification.

Another important consideration is the percentage of processing for each pass thru the filter; that is, nitrification activity thru each pass of the filter is not great, so filtration is based on continuous repeated passes, so the whole consideration is not critical at all.