Anaerobic reactors

[Spare time]

I was curious. If you run a medai reactor with some sort of biomedia in it, where the goal is to have it denitrify (low flow, special biomedia, etc.), wouldn't this most likely end up producing hydrogen sulfide? I know that in general denitrification can produce nitrogen, nitrite, or hydrogen sulfide.

 

[Randy Holmes-Farley Verified Community Expert]

I was curious. If you run a medai reactor with some sort of biomedia in it, where the goal is to have it denitrify (low flow, special biomedia, etc.), wouldn't this most likely end up producing hydrogen sulfide?

As long as the nitrate does not bottom out, organisms find it far easier to consume nitrate than to consume sulfate, so they do not produce hydrogen sulfide.

Yes, if nitrate was completely depleted and there was organic matter remaining to degrade, hydrogen sulfide could be produced.

There is a well understood progression of reactions that I discuss here:

http://reefkeeping.com/issues/2005-12/rhf/index.php#8

from it:

As mentioned above, this order of electron acceptors used to oxidize organic material is oxygen (O2), then nitrate (NO3-), then manganese (Mn++++), then iron (Fe++), then sulfate (SO4--). Researchers can plot the concentrations of these chemicals as a function of depth, and can also associate an ORP with each transition, although some overlap of the chemistries takes place in each zone. The oxygen zone has an ORP of 0 to 600 mV, the nitrate zone is -150 to 550 mV, the manganese zone is -50 to 400 mV, the iron zone is -700 to -150 mV and the sulfate reduction zone is -850 to 0 mV. Consequently, if hydrogen sulfide is being formed from sulfate, the ORP is likely below 0 mv in that region.

 

[Spare time]

Thank you for the reply Randy !

 

[Spare time]

As long as the nitrate does not bottom out, organisms find it far easier to consume nitrate than to consume sulfate, so they do not produce hydrogen sulfide.

Yes, if nitrate was completely depleted and there was organic matter remaining to degrade, hydrogen sulfide could be produced.

There is a well understood progression of reactions that I discuss here:

http://reefkeeping.com/issues/2005-12/rhf/index.php#8

from it:

As mentioned above, this order of electron acceptors used to oxidize organic material is oxygen (O2), then nitrate (NO3-), then manganese (Mn++++), then iron (Fe++), then sulfate (SO4--). Researchers can plot the concentrations of these chemicals as a function of depth, and can also associate an ORP with each transition, although some overlap of the chemistries takes place in each zone. The oxygen zone has an ORP of 0 to 600 mV, the nitrate zone is -150 to 550 mV, the manganese zone is -50 to 400 mV, the iron zone is -700 to -150 mV and the sulfate reduction zone is -850 to 0 mV. Consequently, if hydrogen sulfide is being formed from sulfate, the ORP is likely below 0 mv in that region.

Is there a need to dose some sort of carbon for denitrification? I

 

[Randy Holmes-Farley Verified Community Expert]

Is there a need to dose some sort of carbon for denitrification? I

I'm not sure what you are asking, exactly.

Certainly, organic carbon dosing is done in part to increase denitrification.

Adding lots of denitrification space without extra carbon can also help since there are some organics around in the water.

"anaerobic reactors" would generally involve adding an organic carbon compound, either liquid or solid, to the reactor. Often these are called carbon denitrators.

 

[Spare time]

I'm not sure what you are asking, exactly.

Certainly, organic carbon dosing is done in part to increase denitrification.

Adding lots of denitrification space without extra carbon can also help since there are some organics around in the water.

"anaerobic reactors" would generally involve adding an organic carbon compound, either liquid or solid, to the reactor. Often these are called carbon denitrators.

Yes that it what I was asking. My only concern is that I don't run a skimmer and that it would be an issue in regards to getting bacterial blooms from the non denitrifying bacteria. The only way I can see that from not happening is just dropping a miniscule amount into the reactor pump intake. Carbon is listed in the ingredients in the chaetogro I dose so maybe that would suffice (if that is organic carbon which I assume it is).

 

[Randy Holmes-Farley Verified Community Expert]

Yes that it what I was asking. My only concern is that I don't run a skimmer and that it would be an issue in regards to getting bacterial blooms from the non denitrifying bacteria. The only way I can see that from not happening is just dropping a miniscule amount into the reactor pump intake. Carbon is listed in the ingredients in the chaetogro I dose so maybe that would suffice (if that is organic carbon which I assume it is).

The carbon in it is much too little to be useful in this context, and it is likely a chelating agent to maintain solubility of some of the less soluble trace elements.