Sulfur denitrator experiment

Delphinus · #1 12-27-2006, 02:47 AM

So, bearing in mind I haven't read the section in detail yet, only scanned it, these are the things that caught my eye:

- recommend upflow instead of downflow to avoid compaction
- recommend flow control valve on input not output to avoid pressurizing the unit
- recommend media volume 1% of total tank volume
- something about the reactor height to diameter ratio should be something like 5:1 (I'll have to read more about that one)

My main thinking here is that the flow-through is too high, and the recirc is not enough. I don't know about switching to 1% tank volume as that will need a different reactor, same with changing the height/diameter ratio (actually mine may already be close to that anyhow, give or take). The main thing I'm thinking is switching the flow control valve to the input, leaving the output wide open; changing the flow direction to upflow; potentially scrapping the feed pump (since need to slooooowwww it down even more), and upping the recirc pump from a mag2 to a mag7 or mag9.

Psyire · #2 12-27-2006, 03:20 AM

Your last 2 points revolve around a 1-pass reactor if I'm not mistaken. I don't believe T.R.A. Vol.3 discusses recirculating reactors. (therefore volumes and flow rates are changed)

I wouldn't increase the flowthrough rate of the recirc. chamber if I were you. This will nullify the 'O2-Free' zone if the flow is too much.

You may want to check your test kits as stated above, just in case something is off. I would just run a nitrate test on your new makeup water, during your next water change to see what it reads.

Psyire · #3 12-27-2006, 03:24 AM

If changing your flow through the sulphur chamber I would actually go the other way and lower it. This will create a bigger O2-Free zone and therefore more anerobic bacteria. If your flow is too high I would suspect that you would get into the middle of the denitrification cycle and not have enough anerobic bacteria to finish the cycle off. (which would seem to be what your test results are showing)

Delphinus · #4 12-27-2006, 04:18 AM

No indeed, I want to slow down the flow-through. Sorry if that wasn't clear. That's what I think that's my problem right now, in that there's too much flow-through, even at 1 drop per 2 to 3 seconds, it's too fast. There has been NO sulfurous scent and everything I've read said that a too-slow flowrate will have a scent, and a too-fast flowrate will likely still output nitrates and nitrite. A bigger unit would probably help but that's not what I have to work with so I have to find another means of controlling the flow through this and slow it down considerably.

What I do want to increase though is the power of the pump doing the recirculation inside the reactor. It won't work to increase contact time but I think there's not enough contact with the media in the current arrangement with the mag2.

I've been using three different test kits to take nitrate readings, unfortunately they all agree with each other. Although I only have a test-strip for nitrite, not a full-blown test kit for that, and no secondary testkit with which to compare results. Nitrite's not really a commonly stocked testkit it would seem (I'd never consider buying one if it wasn't for this).

Psyire · #5 12-27-2006, 05:05 AM

Ah.

Well in that case I can't see how your proposed changes could hurt anything. Might want to do one at a time, starting with the cheapest being to slow the flow down 'through' the reactor. Then if that dosen't seem to help, increase the recirculation. That way you don't go the wrong direction twice by accident.

Psyire · #6 12-27-2006, 05:17 AM

Incase you are interested my reactor is going to be an upflow with a eheim 1250 recirculating pump.

I really have a hard time believing a Mag 2 wouldn't be enough for your application. The midwest units use a eheim 1048 which is probably 1/2 the flow of the Mag 2, and their unit is quite big.

Delphinus · #7 12-27-2006, 05:43 AM

One week to cycle ?!

Man ... I feel so ripped off.

Anyhow, I've taken mine offline for now. Will tinker around tomorrow or the next day time permitting .. I agree about the sulfur amounts -- seems to me if it's too small it should just not be able to pull down the tank nitrates as quickly -- but should still cycle and still output zero. At the very least I'm going to swap the pump leads to reverse the flow, and if the recirc pump isn't enough to draw sump water then I'm going to fashion some kind of gravity feed and see how ridiculously slow I can make the flowthrough.

Don't know what to say about the Midwest units using a smaller pump. All I can say is I gave it a month .. and it wasn't cycled so I know something's not right. All I can do is guess at what ... I wish I had more answers.

Pansy-Paws · #8 12-27-2006, 05:10 AM

My sulphur denitrator (sized at 0.8% of volume) dropped 40 ppm to zero in 4 weeks, after one week to cycle the denitrator. It does sound like your flow rate is in the right ballpark, so the O2-free zone must be getting disturbed in some way and not forming. Maybe upflow is the secret, as any nitrogen bubbles would rise back through the O2-free zone in a downflow design

I wouldn't worry about the volume of sulphur. If it's too small, nitrate reduction in your system will simply be slower, and as long as it is sized large enough to counter the new nitrate production, you'll reach zero. Once it's cycled, you'll be able to tell if it's large enough.

I started out with two Phosban 150 reactors (one with sulphur, one with aragonite) to test the concept on my 500 gallon system, well short of 1% volume. With the effluent nitrates at zero for this test system, I knew that a larger design was required.

Myself, I've been having trouble with low pH for the effluent, so am looking to build a recirculation chamber with aragonite on the outflow to counter the problem.

Keep persevering ...