Phosphate Absorption Rates in Aragonite

[Randy Holmes-Farley]

Here is where my theory comes into play. I think that if you put 50 lbs of that sediment into 100L of water and then added 227 ppm of phosphate, I think that it would absorb most if it and the water would have a very low concentration left relative to the start.

I think that it would end up being somewhere around 1.0 (just guessing) in the water. If you put in just enough GFO to treat 1.0 PPM in the water column, you would have to treat 227 times to remove it all.

Does this make sense?

It would not be "very low", because to absorb 10 ug/L the free concentration of phosphate needs to be quite high (~20 uM, or 2 ppm; Figure 9 in the linked article). If you drop the concentration to 0.5 ppm, the amount bound would drop to about 1/3 of that value.

So if you start with that full concentration, then as the free concentration drops, the amount that will ultimately bind drops, and a steady state is eventually reached that might leave quite a lot in solution.

 

[mcarroll]

But that was tissue surface area. You need calcium carbonate surface area, which I showed some rough data for and is far higher.

Like I said it's fine to do the calculation on data you have available.

When I posted I did not see that so go ahead and use that for your calculation.

It seems to me like the calculation they used is pretty similar because I can imagine a piece of live rock having 10 times more surface area than the coral skeleton that was used in the example that I made.

Really curious to see the calculation based on your number.

 

[Randy Holmes-Farley]

Like I said it's fine to do the calculation on data you have available.

When I posted I did not see that so go ahead and use that for your calculation.

It seems to me like the calculation they used is pretty similar because I can imagine a piece of live rock having 10 times more surface area than the coral skeleton that was used in the example that I made.

Really curious to see the calculation based on your number.

The link you posted doesn't work, so I used Millero's data.

Can you give a better link?

 

[Randy Holmes-Farley]

http://www.sciencedirect.com/science/article/pii/0016703778900388

says that

"During the first 10-15 sec approx 2-2.5 umol/m2 of phosphate were adsorbed or 19-24% of the surface was covered. The rate then decreased rapidly and continously over the course of the experiment to about 10-7 umol/m2/sec with a final surface coverage of 5 umol/m2.

So let's look at 2 umol/m2.

According to BRS, Pukani has a surface area of 0.5 m2/g.

That won't all be accessible, but if it is, then it binds 2 umol/m2 x 0.5 m2/g = 1 umol/g.

For 100 pounds of rock, that is 100 pounds *454 g/pound * 1 umol/g = 45,400 umole or 45.2 mmole = 4,540 mg of phospahte.

If that desorbed into 100 liters of water, the concentration would be 45 ppm.

 

[mcarroll]

FWIW, BRS tested the total surface area of some rock types and got about 0.5 m2/g for Pukani. That’s 5,000 cm2 per gram. A hundred pounds of rock has 227 million cm2. Not all of that is likely accessible by phosphate, but a lot of it will be since phosphate is pretty small.

https://www.bulkreefsupply.com/video/view/Which-rock-has-the-most-surface-area/

If you find this data believable, then I trust you. Go ahead and use this. (See below about the PDF for Millero's doc. Looks like you got it already)

The number seems compatible with the Millero data anyway IMO....one stick colony vs a piece of live rock seems like an order of magnitude difference in surface area to me.

Also seems consistent with your sand bed number. I like it!

I really would like any useful point of reference for the potential quantities of PO4 we could really be dealing with in these circumstances.

Of course knowing some experimental results will be great too!!

@jda can you measure surface area for your aragonite like BRS did? (Assuming you're using some rock and not just pure powder.....I'm not sure of their method myself.)

For one particular type of natural calcium carbonate sediment, Millero shows the max absorption is about 10 umole/g

https://link.springer.com/article/10.1023/A:1011344117092

Taking that value, 50 pounds of such sediment would bind 227,000 micromoles (22,700,000 ug, or 22,700 mg) of phosphate.

If that all desorbed into 100 L of seawater, it would give a concentration of 227 ppm.

If you hit Google Scholar with that article's title, you should get a link to the full PDF on academia.edu.

Not sure how Acedemia.edu generate their links but they are apaprently anchored to the google search that generated them somehow....I've had problems saving and sharing links from them before.
(PDF linked below)

But to that calculation you did....

So if that sediment was added to a spanking-new 180 Gallon tank (vs only 100L) than that tank's water would get to about 33 ppm, correct?

(That's PO4 and not just P, right?)

At least in that scenario where there's a lot of mixing and churning of the sediment, we'd probably expect a LARGE rush of PO4 – about 80%....or >26 ppm of PO4....right away. Then the remaining ~7 ppm would "leach out" over the next week+.

LOVE THIS

 

[mcarroll]

Looks like you may have gotten your hands on that Millero PDF already, but just in case I'm just gonna post it here.....lemme know if that's a problem for anyone. (I can delete it, of course.)

 

[Randy Holmes-Farley]

All my numbers were phosphate, not P.

If you loaded up rock with a max load of P, then dropped it into pristine water, it won't all come off unless the water volume is super large and the concentration of phosphate attained when it came off was very low.

 

[mcarroll]

I'm caught up now.....you can disregard most of what I just posted since I think we may have been ediing at the sime time.

(You might like the PDF I attached to one post though.)

 

[mcarroll]

final surface coverage of 5 umol/m2

That won't all be accessible, but if it is, then it binds 2 umol/m2 x 0.5 m2/g = 1 umol/g.

For 100 pounds of rock, that is 100 pounds *454 g/pound * 1 umol/g = 45,400 umole or 45.2 mmole = 4,540 mg of phospahte.

If that desorbed into 100 liters of water, the concentration would be 45 ppm.

If you loaded up rock with a max load of P, then dropped it into pristine water, it won't all come off unless the water volume is super large and the concentration of phosphate attained when it came off was very low.

(Checking my understanding...)

Is 5 umol/m2 ("final surface coverage") the max load?

2 umol/m2 that you used is from the fraction of 5 umol that quickly adsorbs, right?

For your max load in pristine water example, which info are you referring to re: the super large water volume?

And by "very low" do you mean like in a hypothetical brand new aquarium where let's say very large water changes are being done with PO4-free seawater?

 

[jda]

All of my stuff is mostly spherical. I will try and get a mean diameter and weight of a sampling of 8-10 spheres. Will this be good enough? I can do other things if you let me know what to do.

 

[jda]

But to that calculation you did....

So if that sediment was added to a spanking-new 180 Gallon tank (vs only 100L) than that tank's water would get to about 33 ppm, correct?

(That's PO4 and not just P, right?)

At least in that scenario where there's a lot of mixing and churning of the sediment, we'd probably expect a LARGE rush of PO4 – about 80%....or >26 ppm of PO4....right away. Then the remaining ~7 ppm would "leach out" over the next week+.

LOVE THIS

681 liters at a ratio of 227 total to 2 ppm final per 100L... so six (rounding off the 81) times the volume for 1/6th the final concentration in the water. The 33 PPM that could be absorbed would yield a final water concentration of just under .3 ppm. If lower concentration water is never introduced, the rock will never unbind more.

The water will not have 26 PPM. .3 ish is as high as it will go.

I cannot get the article to open where I can see chart 9, but it appears from just Randys posts, that in 100L of water 227 total PPM will yield about 2.0 in the water, where as about 75 total PPM is about .5. If you chart this out in just a linear fashion (who knows) and adjust for 180G to 100L, then it is just under .3 in the water.

At 1 tbsp of GFO per 4 gallons of water, you can see how this would take a lot of time and reactors to get it all out of the rocks. The reports of it taking between one and two year are quite reasonable (and common). Also, once inhabitants get in the tank, you cannot bounce the level from .3 to zero all of the time until it all goes away (the .3 will slowly go down each time) - smart folks will want to go slow with this.

 

[Randy Holmes-Farley]

(Checking my understanding...)

Is 5 umol/m2 ("final surface coverage") the max load?

2 umol/m2 that you used is from the fraction of 5 umol that quickly adsorbs, right?

For your max load in pristine water example, which info are you referring to re: the super large water volume?

And by "very low" do you mean like in a hypothetical brand new aquarium where let's say very large water changes are being done with PO4-free seawater?

The graphs run up to more than 10 umol/m2 as the phosphate concentration rises. I just picked a value (5 umol/m2) that might reflect what you might attain. There's no way we can calculate these things to within a factor of 2 anyway since accessible surface area is not known, even with BET testing. Gases used for these surface area measurements (as BRS did) get into smaller spaces than phosphate in water will.

My comment on a super large volume of water was just pointing out that there is an equilibrium between phosphate on and off. if you start with loaded rock and put it in a small volume of water, the phosphate concentration in the water will get high. if you put it is a super large volume of water, the phosphate concentration in that water will be very low by dilution. The larger the volume the lower the free concentration will be at equilibrium.

 

[Cory]

Is the purpose here to add fresh caco2 to reduce po4 instead of using gfo or al02?

 

[Randy Holmes-Farley]

I think the main purpose is just to understand an effect we think we see, but none have actually measured carefully: the amount of binding of phosphate to rock or sand in a typical reef tank under typical conditions.

 

[mcarroll]

Is the purpose here to add fresh caco2 to reduce po4 instead of using gfo or al02?

That's a fun angle to think about....I guess we'd have to admit it's safer than the other two, if not more effective. LOL

 

[mcarroll]

@jda could you open the attachment on post #26?

 

[jda]

The article was not accessible when I tried last week... but I have new a method to try when I get time. ...we just adopted two kids from eastern Europe, so they sometimes need large chunks of our time as they learn English... so I am in/out quite a bit in the last few weeks.

A guy on RC about a decade ago used to try and convince people to use crushed coral substrate to manage phosphates - cheap, safe, available. He was laughed off of the board, but he was not wrong, IMO. This was about the time that sand was blamed for leeching phosphates and ruining tanks after a few years... not many could understand that they sand was not leeching anything, rather just not binding enough anymore to cover up bad husbandry habits.

The real issue with CaCo3 is that it might be really hard to get some that is truly phosphate free and is porous enough to be effective. I have thought about CaCO3 for years, but the manmade stuff for reactor media that really is phosphate free is dense as granite(this is hyperbolic, but it is dense) , and the natural stuff probably has some small level phosphate in it already. I think that it could probably work on tanks with medium to high concentrations of free phosphate, but good luck trying to convince a hobbyist since all that they know is the word "leech" and they will think that the minimal amount in the CaCO3 will get into their tank instead of actually removing the stuff.

It could get quite cost effective if CaCO3 will unbind with freshwater where a station could be made with a dosing pump, float valve and a heater to systematically wash away the water with unbound phosphate and replace it with fresh.

The phosphate, nor my Hannah high level checker, have came yet. I am still letting the media soak to see if they release any P - why not since I have time.

 

[mcarroll]

Is the purpose here to add fresh caco2 to reduce po4 instead of using gfo or al02?

Well I'll be....
Calcium Carbonate Phosphate Binding Ion Exchange Filtration and Accelerated Denitrification Improve Public Health Standards and Combat Eutrophication in Aquatic Ecosystems

Especially in Madrona Marsh, one of the last remaining vernal marshes in the greater Los Angeles area, California, cultural eutrophication has become a major problem. In this study, calcium carbonate was found to be an excellent phosphate binder, reducing up to 70% of the phosphates in a given sample of water, and it posed relatively negligent ecological repercussions.

The funny part is that I didn't even go looking for this....I had a search open for "fungus coral holobiont" at PubMED from a couple days ago and this was one of a dozen "related links" in the sidebar! I'm glad it caught my eye!

(I dunno if we'll see this done in aquaria, but it's still a cool article and awesome serendipity. )

 

[jda]

Remote deep sand beds where used as take-away phosphate sponges and nitrate factories. ...only downside was the time to repopulate the anoxic sections after removing some/all of the and.

Am I dating myself too much? Does anybody even know what a remote DSB is anymore?

 

[mcarroll]

Am I dating myself too much?

I can't even hear you unless you're talking about bio-pellets.