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rsman, thanks for that.
I've been through the thread again, and I can't understand why the coil can be too long or why there can be too much media in the chamber -- in other words, how can a denitrator be too big?
This is how I see it, and you can correct me so I understand. If there's something I should read, maybe you could point me in that direction. Please bear with me.
1. The coil tube receives water rich in O2 from the pump.
2. As bacteria colonise the tube, you have aerobics oxidising the organics and producing ammonia, nitrate and nitrate.
3. As long as oxygen lasts, oxidation will occur. The slow progress of the water ensures maximum contact time.
4. The aerobics will colonise as far along the tube as oxygen lasts.
5. When oxygen runs out, anaerobes start colonising the inside of the tube.
6. So part of the tube will be aerobic and part anaerobic.
7. When the water reaches the anaerobics in the tube, denitrification commences.
8. When the water leaves the bottom of the coil, it passes through the media in the chamber with a reduced amount of nitrate.
9. Whatever nitrate is left is then processed by the anaerobes living on the media.
So if a coil is 50 feet long and (just to pick a figure) the first 30 feet of it are aerobic, the last 20 feet are anaerobic. I'm not able to understand why another 50 feet of coil is a problem, as it too would be populated by anaerobes. Aerobic oxidation would be completed in the first 30 feet of the coil, and anaerobic denitrification will occur in the remaining 70 feet of the tube. I would have thought this would be a good thing.
If the chamber contains (say) one quart of media, the anaerobes here will process whatever nitrate is available. If you double or triple the amount of media, you are still treating the same amount of nitrate. The same number of bacteria will be present in the two or three quarts as there would be if you had only one quart (only enough bacteria will form according to the amount of nutrient).
I can understand that having a coil longer than necessary and more media than needed may be a waste of materials, but I can't imagine why it's not a good thing. I would have thought that the extra coil and media would provide extra capacity for more bacteria in case the system ever needs to process more than expected.
This is all based on an identical flow through the chamber irrespective of size.
That's why I planned to build a denitrator bigger than I really need -- a bit like having a skimmer bigger than needed in case something goes wrong, or having an extra heater in the tank in case of extra-cold weather or a failure of a heater.
Sorry for rambling on so much, but I needed to explain how I think (which is probably simplistic). You seem to be very knowledgable and I've no doubt you've got good reasons for your comments. I'm not challenging what you say. I'm the kind of person who likes to know why I'm doing what I'm doing.
As I said, if there's something I need to read, I'd like to do that. If you feel up to explaining this to me, I'd very much appreciate it.
Many thanks.
Les
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