My new sulphur denitrator setup

[Delphinus]

Hmm .. interesting. I would have guessed those rocks would be OK but who knows. Well it's just like my situation really, mathematically there's no reason for me to have had nitrates above 50 in the first place but it's been fairly consistent, and I've tried just about every other trick in the book (and gone though at least 4 tank setups as well). I guess sometimes it just happens ...

On the bright side it's down to the mid 20's now and appears to be coming down nicely still.

[untamed]

I'm really interested in this.

Sorry for tons of questions...
1) The sulfer based reaction has no need for low pH or CO2 addition, right?
2) Do you add CO2 to the Ca reaction chamber?
3) Is the Ca reaction chamber recirculated? Is the Nitrate reaction chamber recirculated? Both?
4) Do you have an additional Ca reactor, or is this your only Ca reactor?
5) Why the ORP sensor in the Nitrate chamber? Does the sulpher reaction also need to be in the absence of oxygen? If so, how is oxygen removed from this reactor?
6) Do you attempt to vent the N2 produced?...

Here's what Holmes-Farley had to say about it. I believe this was written in 2003.

Use a sulfur denitrator. In these systems, bacteria use elemental sulfur and produce N2 from it and nitrate according the following equation (or something similar):

2 H2O + 5 S + 6 NO3- à 3 N2 + 5 SO4-- + 4 H+

It has also been suggested to pass the effluent of such a reactor through a bed of aragonite to use the acid (H+) produced to dissolve the calcium carbonate, and thereby provide calcium and alkalinity to the aquarium.

While that is a fine idea, it doesn’t add much calcium and alkalinity to most aquaria.

To estimate the magnitude of the effect, we start with a liberal estimate of how much nitrate might be removed. Say 10 ppm of nitrate per week.

10 ppm nitrate = 0.16 mmole/L of nitrate

Since 4 moles of H+ are produced for every 6 moles of nitrate consumed, this will produce

0.107 mmoles/L of H+ per week

How much calcium this could produce?
Assume that it takes one proton to dissolve one calcium carbonate:

CaCO3 + H+ ßà Ca++ + HCO3-

Clearly, this is a substantial overestimate because much of the acid will be used up driving the pH down to the point where CaCO3 can even begin to dissolve. Consequently, we have an upside limit of

0.107 mmoles of Ca++ per week

since calcium weighs 40 mg/mmol, that's

4.3 ppm Ca++ per week.

For comparison, an aquarist adding 2% of the tank volume in saturated limewater daily is adding on the order of 16 ppm of calcium per day. Consequently, this method may not be especially useful for maintaining calcium and alkalinity levels. On the other hand, the acid produced will have a long term lowering effect on the alkalinity, so if you use it, watch the alkalinity.

As to its actual ability to reduce nitrate, I cannot say for sure. I expect that it can be made to work, but the only aquarist that I have spoken to that uses one has had considerable difficulty with it.

[Delphinus]

Ask away! (Not speaking for Psyire of course, but I'm hoping he doesn't mind).

Originally Posted by untamed

I'm really interested in this.

Sorry for tons of questions...
1) The sulfer based reaction has no need for low pH or CO2 addition, right?

Errr .. yes and no. No as in you don't inject CO2 to lower the pH, but you DO need a zone of "little to no" oxygen (aka "anoxic zone" or "anaerobic zone") for the anaerobic bacteria that reduces nitrate, to take hold. They metabolise the sulfur, consuming the nitrates and releasing nitrogen gas, and sulphates (see your RHF text you quoted). NSW already has sulfate to some degree and there's nothing in the literature to suggest that it's harmful in any way.

2) Do you add CO2 to the Ca reaction chamber?

No - the absence of oxygen plus the metabolic activities reduce the pH in the reactor, so the water entering the Ca reaction chamber is already with depressed pH.

3) Is the Ca reaction chamber recirculated? Is the Nitrate reaction chamber recirculated? Both?

The Ca reaction chamber is the second stage of a 2 stage calcium reactor. These are almost always single-pass, otherwise you're basically looking at a complete reactor for the second stage. I imagine there is benefit for recirc on this stage but it's fairly atypical thing, based probably mostly on economics. I've been considering making my 2nd stage recirculation at some point but it's not a priority. The flow-through flowrate is very slow.

The nitrate reducing chamber, or the first stage, is recirculated. This part is basically the same as any calcium reactor.

4) Do you have an additional Ca reactor, or is this your only Ca reactor?

Technically I think you're better off not relying on the denitrator to replenish Ca and Alk on a heavy Ca drawing bioload (ie. SPS, clams, etc.). Personally I have several reactors anyhow as I'm a gear nerd and like trying different things so in my case the answer is "yes I have an additional Ca reactor" but at the moment the tank I run my denitrator on has a very low Ca demand as there are no corals in there for now. So no other reactor on THAT tank but that may change one day.

5) Why the ORP sensor in the Nitrate chamber? Does the sulpher reaction also need to be in the absence of oxygen? If so, how is oxygen removed from this reactor?

I can't answer the ORP thing, maybe Psyire can chime in on that one. In my opinion, ORP is a useless number to track unless you're running ozone on your system.

The sulfur reaction does need to be in the absence of oxygen.

Oxygen is removed by cycling the reactor and using a very slow flowrate. Thus, once the oxygen is depleted, very little returns into reactor from the feed.

There is a slight caveat. Once the unit has "cycled completely" and after a period of time the tank nitrates will read zero. At this point you need to increase the flowthrough rate through the reactor so that nitrate can be consumed at the rate it is produced.

So technically you don't want an completely oxygen-free zone, as if you do that, you'll have the wrong chemical reaction take place, and produce H2S instead. Apparently the levels are so low as to generally not be a concern other that it will stink your place to high heaven. But you do want a "low" oxygen zone until your tank is reading zero nitrates and then you rely on a smaller population of bacteria with the faster flowrate.

6) Do you attempt to vent the N2 produced?...

It is recommended to place the output of the reactor in a high turbulent zone, preferably a sump not the main tank, and above the waterline to aid in gas exchange. Other than that, no special consideration for venting N2 (which is a part of air anyhow), except for that the first stage, i.e. the sulfur stage, should be an upflow so that gas can escape into the second stage (which should also be upflow so gas can escape from there as well). A downflow style will end up with a gas bubble at the top that can't go anywhere.


Hope this helps..

[Delphinus]

If you want more reading, try these:

http://www.canreef.com/vbulletin/sho...d.php?t=28791&
http://www.canreef.com/vbulletin/sho...d.php?t=26299&
http://www.canreef.com/vbulletin/sho...d.php?t=26313&

[Psyire]

Tony answered the above questions well, but I can definately add some info regarding ORP.

The denitrification process taking place in the sulphur media is one of reduction and requires an anerobic condition. An ORP value of -50 to -300 is perfect for the stabilization of these anerobic bacteria. Higher than -50 and you get too much oxidization or oxygen present, and lower than -300 and you get a byproduct of Hydrogen sulfide. (H2S) The ORP probe is in there to monitor ORP so I am better able to adjust my 'flow, or drip rate' through the reactor. This will inable me to have the best possible environment for these anerobic bacteria at all times. Atleast that is the theory behind it...

[Psyire]

So I now have the unit running on around 15g of water I just pulled from my tank during a water change. I have the drip rate set at about 3 per/second and I plan to leave it that way until the effluent tests zero for nitrate. The water is currently reading about 30 ppm of nitrate.

Here is a picture of the setup:


note* Probe ports and flow meter will not be used until unit is cycled.

[Delphinus]

What test kit are you planning to use to test the effluent?

FWIW I can't get my effluent to zero nitrates yet. It's been steady at 13ppm for the last week so I slowed it down a bit last night and will retest after 24 hours again. Actually before I hijack this thread any worse I'll go update my own with the latest results because there are some headaches there again.