Does Carbon Remove Useful Things?

[Belgian Anthias]

Sun light will make algae grow rapidly and like crazy.

In case, why don't they do it, grow like crazy? In a closed system it would ensure that nutrients cannot accumulate. In a closed system, growth is the most important regulator, it can be easily harvested and managed.
Why is safely stored and usable nitrogen in the form of nitrate not used up in a well-lit aquarium? The constant removal of some of the dissolved organic substances creates an imbalance between the availability of inorganic compounds and other nutrients necessary for balanced growth and the removal of all nutrients by sunlight-driven growth is therefore made impossible. Natural denitrification is nothing more than anaerobic mineralization of organic waste. In normal circumstances, +- 15% (heterotrophic + autotrophic) of the nitrogen is exported by natural denitrification and there should be a shortage of usable nitrogen, a growth-regulating factor. Nitrogen that accumulates is not the growth regulating factor.

The use of GAC removes organic matter, but it does so very selectively and does not remove inorganic nitrogen and phosphorus compounds, resulting in disruptive growth when changes in the removal pattern occur. In a sense, the same can be said of a skimmer. Management of the nutrient availability starts with what is added, the C/N ratio of food.

 

[Mr. Mojo Rising]

I've been trying to find out if activated carbon will remove phytoplankton. Anyone know? Cannot find any info about that.

 

[Randy Holmes-Farley Verified Community Expert]

GAC "adsorbs" a lot of different things at different rates (pedantic, but absorbtion incorporates the material, adsorption builds it up on the surface). I believe that metals don't adsorb as well to GAC as organic compounds, but that iodine does. Here's a table i googled describing some of the things that GAC does or doesn't adsorb well https://www.sentryair.com/activated-carbon-adsorption.htm

However, i dont think theres much concern of taking out good things too much. Most people have very successful reefs with GAC!

That link you posted is for gas absorption. Iodine as I2 gas certainly absorbs on GAC. In seawater, iodine is present as iodide and iodate, and I do not believe it adsorbs well on GAC, though I have not seen anyone test it.

 

[Randy Holmes-Farley Verified Community Expert]

I've been trying to find out if activated carbon will remove phytoplankton. Anyone know? Cannot find any info about that.

No, it won’t bind organisms except those such as benthic bacteria that want to grow on it.

 

[mizimmer90]

That link you posted is for gas absorption. Iodine as I2 gas certainly absorbs on GAC. In seawater, iodine is present as iodide and iodate, and I do not believe it adsorbs well on GAC, though I have not seen anyone test it.

Iodide still adsorbs pretty well in solution! Check figure 1 and 11 of this paper that shows iodine removal of ~25% w/w iodine/adsorbant (acetic acid solution) and even better adsorption of iodide in water!

https://pubs.acs.org/doi/pdf/10.1021/ie00020a023

this other paper shows similar results and also the pH dependence of adsorption (lower pH, around 5, is significantly higher adsorption).

https://pubs.acs.org/doi/epdf/10.1021/es010972m

 

[Randy Holmes-Farley Verified Community Expert]

Iodide still adsorbs pretty well in solution! Check figure 1 of this paper that shows iodide removal of ~25% w/w iodide/adsorbant!

https://pubs.acs.org/doi/pdf/10.1021/ie00020a023

this other paper shows similar results and also the pH dependence of adsorption (lower pH, around 5, is significantly higher adsorption).

https://pubs.acs.org/doi/epdf/10.1021/es010972m

I do not believe that either paper shows or even suggests that significant iodide or iodate will bind to GAC from seawater at the iodine concentrations found in seawater. That is the data that has not, as far as I know, been shown. These papers test very different things.

The first paper is totally useless in our context. It is looking at I2 and HI absorption, which are not the forms present in seawater. There also are no competing ions present in any of the test fluids.

"In a static test,20 mL of acetic acid containing 800 ppm I2 and 10-200 mg of adsorbent were equilibrated in a flask for 24 h at room temperature. After filtration, the amount of iodine removed from filtrate was determined from the decreasein the intensity of 474-nm ultraviolet (UV) absorbance of the solution."

The second paper uses a low ionic strength fluid, which means it has very few competing ions to the iodide for charged binding sites on the GAC. The ion concentration is:

". The ionic strength ranged between 0.05 and 0.09 M as NaCl."

Seawater has an ion concentration a factor of ten higher, meaning 10x more competition. More importantly, it also contains ions with multiple charged ions (such as sulfate) which can bind more strongly to charged surfaces than single charged ions such as chloride or iodide, as it known with ion exchange resins:

"This works because the anion resin has more affinity for the nitrate or sulphate ion than for the chloride ion, the order of affinity being: SO4-- > NO3– > Cl– > HCO3– > OH– > F–"

https://www.lenntech.com/Data-sheets/Ion-Exchange-for-Dummies-RH.pdf

The second paper also tests only at what would be very high iodine concentrations (compared to seawater). The lowest test point for normal GAC at pH 8 on Figure 2 is about 2 uM, or 252 ug/L or 0.3 ppm. That's 5 times higher than the iodide concentration in normal seawater.
The binding is also so low that the whole purpose of the paper is to get better binding using GAC which has silver bound to it, which they showed.
Thus, the second paper uses a higher iodide concentration in a fluid with less ionic competition to test binding. Consequently, I do not think it tells us anything about what would happen in a reef tank.

 

[mizimmer90]

I do not believe that either paper shows or even suggests that significant iodide or iodate will bind to GAC from seawater at the iodine concentrations found in seawater. That is the data that has not, as far as I know, been shown. These papers test very different things.

The first paper is totally useless in our context. It is looking at I2 and HI absorption, which are not the forms present in seawater. There also are no competing ions present in any of the test fluids.

"In a static test,20 mL of acetic acid containing 800 ppm I2 and 10-200 mg of adsorbent were equilibrated in a flask for 24 h at room temperature. After filtration, the amount of iodine removed from filtrate was determined from the decreasein the intensity of 474-nm ultraviolet (UV) absorbance of the solution."

The second paper uses a low ionic strength fluid, which means it has very few competing ions to the iodide for charged binding sites on the GAC. The ion concentration is:

". The ionic strength ranged between 0.05 and 0.09 M as NaCl."

Seawater has an ion concentration a factor of ten higher, meaning 10x more competition. More importantly, it also contains ions with multiple charged ions (such as sulfate) which can bind more strongly to charged surfaces than single charged ions such as chloride or iodide, as it known with ion exchange resins:

"This works because the anion resin has more affinity for the nitrate or sulphate ion than for the chloride ion, the order of affinity being: SO4-- > NO3– > Cl– > HCO3– > OH– > F–"

https://www.lenntech.com/Data-sheets/Ion-Exchange-for-Dummies-RH.pdf

The second paper also tests only at what would be very high iodine concentrations (compared to seawater). The lowest test point for normal GAC at pH 8 on Figure 2 is about 2 uM, or 252 ug/L or 0.3 ppm. That's 5 times higher than the iodide concentration in normal seawater.
The binding is also so low that the whole purpose of the paper is to get better binding using GAC which has silver bound to it, which they showed.
Thus, the second paper uses a higher iodide concentration in a fluid with less ionic competition to test binding. Consequently, I do not think it tells us anything about what would happen in a reef tank.

I dont want to die on a hill that wasn't the point of my first post lol, so I'll reiterate that my position is in agreement with you that this isn't a major concern for saltwater tanks!

But GAC "can" and "does" adsorb various "good" things (though not at appreciable levels in our reef tanks).

 

[Randy Holmes-Farley Verified Community Expert]

I dont want to die on a hill that wasn't the point of my first post lol, so I'll reiterate that my position is in agreement with you that this isn't a major concern for saltwater tanks!

But GAC "can" and "does" adsorb various "good" things (though not at appreciable levels in our reef tanks).

I wish we had more real world data, I would not be surprised if GAC exports an important amount of trace elements that themselves bind to organics, but how significant that is can only be tested with real tank water, not simulated fluids.

 

[mizimmer90]

I wish we had more real world data, I would not be surprised if GAC exports an important amount of trace elements that themselves bind to organics, but how significant that is can only be tested with real tank water, not simulated fluids.

Definitely!! Could be an interesting experiment for the research forum!

I.e. measure trace elements in prepared saltwater, then pass it over varying amounts of GAC, and measure afterwards! The difficulty will be in the accuracy/precision of home test kits along with the hyper params of contact time/flow/equilibration with the GAC.

 

[Belgian Anthias]

I've been trying to find out if activated carbon will remove phytoplankton. Anyone know? Cannot find any info about that.

Definitely!! Could be an interesting experiment for the research forum!

I.e. measure trace elements in prepared saltwater, then pass it over varying amounts of GAC, and measure afterwards! The difficulty will be in the accuracy/precision of home test kits along with the hyper params of contact time/flow/equilibration with the GAC.

More info about GAC. Feldman has conducted and published research regarding the use of GAC in seawater aquariums. Links to his articles are available as references. Ken S. Feldman, Lauren F. Vernese, Karl T. Mueller, Kelly M. Maers Chemistry Department, The Pennsylvania State University ( 2008)

 

[Randy Holmes-Farley Verified Community Expert]

More info about GAC. Feldman has conducted and published research regarding the use of GAC in seawater aquariums. Links to his articles are available as references. Ken S. Feldman, Lauren F. Vernese, Karl T. Mueller, Kelly M. Maers Chemistry Department, The Pennsylvania State University ( 2008)

Unfortunately, I don't believe any of Ken's article detail what is removed by GAC, except very broad categories such as total organic carbon.

For example:

Total Organic Carbon (TOC) and the Reef Aquarium: an Initial Survey, Part II

Department of Chemistry, The Pennsylvania State University, University Park, PA 16802. Ken and Kelly continue to report on their work on Total Organic Carbon and how it relates to the reef aquarium.

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