Sulfur Denitrators and Carbon

[rclendan]

I am experimenting with my 24" DIY recirculating S-Denitrator with a mixed bed consisting of ~1 liter of sulfur prills and ~2 liters of aragonite media. I have a 10 inch cartridge filter holder full of ceramic media plumbed before the unit to add some surface area for aerobic bacteria to consume oxygen and lower the ORP. I have installed some injection ports in the feed line and in the denitrator body so I can feed carbon in the form of sugar solution. I also maintain the unit at 90 degrees F (32 degrees C) for optimal denitrification. when I run the unit without any supplemental carbon, I can only get a relatively small amount of 0 ppm nitrate 1-2 drops per second (< 1 liter per hour) effluent, but when I drip 0.15% sucrose solution at (~15 drops per minute) into the inlet line, I can run the unit at 3-4 liters per hour with 0 ppm effluent. I assume the carbon is either contributing the sulfur denitrating bacteria's biomass, or it is being consumed by aerobic bacteria in the pre-chamber, accelerating the drop in ORP (probably a bit of both), allowing for a higher flow rate. Direct carbon addition also speeds up the cycle (< 1 hour in some cases) when starting, or after opening the unit for cleaning.

The difficulty is in determining the carbon consumption of the unit as not to introduce stray carbon into the aquarium. It is also fiddly to maintain a steady carbon the drip rate. I'd rather dose a small amount of CO2 directly (6-10 bubbles a minute, keeping the pH around 6.8) and get some benefit from the calcium reaction while feeding the carbon fixing bacteria.

Anybody have experience with this? Has anybody tried using CO2 with these units.

[Greg 45]

I am running a large sulfur denitrator only sulfur in the unit. ORP inside the unit reads -180 hope this helps. I do not dose anything into the reactor , running 30 to 40 ml through the reactor out put is 0 nitrates.

[CHSUB]

i run a sulfur denitrator also with orp between -260 and -200; effluent @ 0.00. i find it interesting that your feeding it a carbon source. i would like to process more water, maybe this is the answer? however, co2 is not going to feed the bio-mass?

[rclendan]

Thanks... i should be able to run this unit without additional carbon, i am not sure why i cannot. I can say, sugar dosing does allow for increased flow rate if you were to try it. Especially if you are openning it for cleaning. Before you close it up add a small amout of sugar 100mg or so, and it will cycle very fast. Bob Fenner suggested CO2 addition, as well as sugar to enhance the flow rate. http://www.wetwebmedia.com/SulfurDenitratrF.htm

I assumed that since the denitrifying bacteria were carbon fixing, they would benefit from the addition of CO2. After all, Isn't that how they obtain carbon in your non dosed units?

[CHSUB]

co2 is used to lower ph some to disolve the argonite more, adding CA to the effuient(ie. calcium reactor). however, it has nothing to do with feeding the bio-mass. IMO, not a good idea!

[rclendan]

I'm pretty sure Thiobacillus denitrificans does fix CO2 right out of the water.

From: microbewiki:

"Studies on fixation of carbon dioxide of T. denitrificans found that it is capable of synthesizing hexose phosphates from carbon dioxide by a cyclic mechanism which is similar to that found in green plants. This discovery not only indicates different mechanisms that influence CO2 fixation efficiencies of T. denitrificans, but also provides some insight into the unusual ability of the species to oxidize sulfur compounds under aerobic and denitrifying conditions."

H2S + HS- + NO3- + CO2 + HCO3- + NH4+ --> SO42- + N2 + C5H7O2N (biomass) + H+ + H2O

At any rate, I am going to do some experiments with CO2 in my reactor to see if there is any denitrification benefit from adding CO2. I will post the results.

[CHSUB]

I'm pretty sure Thiobacillus denitrificans does fix CO2 right out of the water.

From: microbewiki:

"Studies on fixation of carbon dioxide of T. denitrificans found that it is capable of synthesizing hexose phosphates from carbon dioxide by a cyclic mechanism which is similar to that found in green plants. This discovery not only indicates different mechanisms that influence CO2 fixation efficiencies of T. denitrificans, but also provides some insight into the unusual ability of the species to oxidize sulfur compounds under aerobic and denitrifying conditions."

H2S + HS- + NO3- + CO2 + HCO3- + NH4+ --> SO42- + N2 + C5H7O2N (biomass) + H+ + H2O

At any rate, I am going to do some experiments with CO2 in my reactor to see if there is any denitrification benefit from adding CO2. I will post the results.

ok, seems i'm wrong...however the co2 will lower the ph some and i've read the optimum ph is around 7.0..... interested in your results, the more water processed the better.

[EnderG60]

You mentioned a chamber with ceramic media before the denitrator. You may want to try removing that.

I had an arragonite chamber after mine and was having major issues till I took it off and tested the water in it. Nitrates were like 40 in the chamber.