GAC Absorbs Nitrate?

ReefHero · Feb 5, 2015

Hi,

Recently on our local forum we had an ongoing debate on whether or not GAC can actually absorb nitrate..... Everything I have read in this reefing hobby suggests to me that it does not actually absorb nitrate. According to Randy Holmes Farley it can absorb organics and metals which could potentially break down into nitrates.....atleast this is what I have gathered from reading his articles. However, there seems to be a few people on my local forum who are still convinced that it does in fact directly absorb nitrate. They even went as far as to post links to various things (none of which are actually directly related to aquarium reef keeping) about how carbon has actually absorbed nitrates..... Here are those links....

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REMOVAL OF AMMONIA FROM AQUACULTURE WATER USING MAIZE COB ACTIVATED CARBON - ResearchGate

Activated carbon and chemical aquarium filtration - Algone

Removal of nitrate from aqueous solutions by activated carbon prepa... - PubMed - NCBI

Water quality information - Can granular activated carbon (GAC) filtration systems trap nitrate and then download it at high enough concentrations to be of concern? | APEC Water

So here is my question guys and specifically at Randy Farley-Holmes (sorry to drag you into this Randy), does GAC absorb nitrates?????

ReefHero · Feb 6, 2015

Bump. Anyone want to give some input on this?

Shep · Feb 6, 2015

It will not bind nitrate, it binds organic compounds.

Randy Holmes-Farley · Feb 6, 2015

I can't read the links now as I'm on a phone, but without a doubt GAC cannot bind appreciable nitrate from seawater. Even in freshwater, for GAC to bind nitrate would require it to have positive charges on its surface (it doesn't), and in seawater there are huge concentrations of similarly charged ions (chloride and sulfate, especially) to compete for binding sites.

ReefHero · Feb 6, 2015

Thank you very much for your replies!!! To be honest Randy the links are very vague and raise a lot of flags.... I cannot detect any nitrates in my system using standard test kits but I am hoping another reefer I know who does have a decent amount of detectable nitrates in their system can help me perform a test. We were going to run about 5g of water through BRS ROX carbon and then test that water to see if there is any noticeable difference in no3 compared to the tank water itself.
I was and still am quite confident that we will see no difference in readings....
I have performed this similar test on my GFO reactor and I am able to read noticeable differences between the input and output using a phosphate test kit.
If you get a chance, I'd like to hear your feedback regarding the links that were used to reference GAC absorbing nitrates.

zesty · Feb 6, 2015

From what I understand. I have not the details at hand, but I was talking to someone (smarter than me) on the subject. He explained how nitrates are very hard to remove from the water. That's why one of the best ways to get nitrates down is a good ole fashioned water change.

Is this close to correct?

ReefHero · Feb 6, 2015

zesty said:
From what I understand. I have not the details at hand, but I was talking to someone (smarter than me) on the subject. He explained how nitrates are very hard to remove from the water. That's why one of the best ways to get nitrates down is a good ole fashioned water change.

Is this close to correct?

I'd say you are correct as long as your NSW contains little to no nitrates. However, I don't think this method is the greatest either when dealing with higher values of nitrates......seems like the best methods are talked about in the latest r2r online magazine.

zesty · Feb 6, 2015

ReefHero said:
I'd say you are correct as long as your NSW contains little to no nitrates. However, I don't think this method is the greatest either when dealing with higher values of nitrates......seems like the best methods are talked about in the latest r2r online magazine.

I can see your point there. :yo:

Randy Holmes-Farley · Feb 7, 2015

zesty said:
From what I understand. I have not the details at hand, but I was talking to someone (smarter than me) on the subject. He explained how nitrates are very hard to remove from the water. That's why one of the best ways to get nitrates down is a good ole fashioned water change.

Is this close to correct?

A water change can certainly remove some of it, but won't easily get you to desirable levels if you have substantially elevated nitrate. More effective ways including organic carbon dosing of various sorts (liquid or pellets), growing macroalgae, ATS, denitrators of various sorts, deep sand beds, or specialized media designed to have anoxic regions inside of them.

This has more, which just published a few days ago:

Nitrate in the Reef Aquarium - REEFEDITION

Randy Holmes-Farley · Feb 7, 2015

Now I can see the links.

The first is obviously fresh water, where there is no big competition for binding sites as there is in seawater. It does not suggest GAC will work in seawater. One concern with such studies is that GAC is a good substrate for bacteria. I cannot get the full text, so I cannot be sure that what they saw wasn't bacterial growth in the GAC.

The second deals with ammonia, and again, not in seawater. Says nothing about nitrate that I could see.

The third doesn't mention nitrate, except in advertisements on the same page.

The fourth has the same issues as the first since I cannot see the full text; not in seawater and concerns that effect might be from bacteria.

The last article is a rambling discourse that doesn't really show anything, but is in freshwater again, and seems more concerned with nitrate being produced on the GAC by nitrification by bacteria, rather than binding of the nitrate.

ReefHero · Feb 7, 2015

Thank you very much for checking out the links. Yeah a couple of them I really shouldn't have even bothered posting here to be questioned.... Sorry.
Ok, so you are suggesting that in freshwater GAC could or would be helpful at absorbing no3? Or you would lean more toward the bacteria growth within the GAC absorbing the no3, even in freshwater?
With that said, could it be possible to grow bacteria within our carbon reactors in order to keep nitrates under control? Or is this useless in the long run because we need to change our carbon out every so often?

Randy Holmes-Farley · Feb 7, 2015

With some types of GAC, there may be a small number of binding sites for negatively charged ions, but it won't bind nearly as much nitrate in fresh water as an ion exchange resin would, and won't bind any in seawater.

All GAC gets lots of bacteria on it, and in some systems where organic carbon is dosed it might be a major site, but it is not optimal for nitrate reduction. Porous substrates would be better for that.

ReefHero · Feb 7, 2015

Thank you Randy for your input. I appreciate your insight on this matter. One last question, during water filtration in large water treatment plants what role does carbon play? I only ask because again it was brought up during our local discussion and one person who claimed to talk to higher ups at these plants said that carbon was used to remove nitrates from the water in these water treatment plants. He went on to explain that the plants also have to backwash the carbon every so often and also something about heating the carbon up improves how it will absorb no3 from water in water treatment plants. Is there any truth to these claims? And again what role does the carbon play in water treatment of our drinking water?

Randy Holmes-Farley · Feb 7, 2015

Carbon is generally used to remove organic matter (which can smell), or catalyze the breakdown of chlorine and chloramine. Whether it binds nitrate in fresh water is totally irtrelevant to seawater where there is so much competition for bindign sites.

Think of it this way: a DI resin binds nitrate perfectly well from fresh water. But it won't in seawater because the chloride and sulfate take up the same sites and are present at many orders of magnitude higher concentration. So it fails to lower nitrate from seawater. Same effect on GAC.

FWIW, the Massachusetts Water Resources Authority uses many methods to purify my water, but not GAC.

This company sells to municipal water companies, and this is what they say it does for them:
Drinking Water Solutions

[h=2]For Municipalities - Activated Carbon[/h]Granular activated carbon (GAC) is a very reliable solution for a variety of water treatment challenges, and more water providers are adopting it every year. Use of GAC provides water utilities with an efficient and cost-effective means to prevent the formation of disinfection byproducts (DBPs) while also removing other organic contaminants found in both surface water and groundwater.
GAC also removes compounds that cause unpleasant taste and odors in drinking water. It provides an effective barrier against many of the endocrine disrupting compounds as well as pharmaceutical and personal care products now found in our water supplies. Most importantly, GAC accomplishes all of these tasks simultaneously, providing water utilities with a single process to solve multiple problems.
As a leader in the activated carbon industry, Calgon Carbon offers a host of GAC products, systems and services:

Granular activated carbon for treatment of taste and odor, disinfection byproducts, emerging contaminants, and other dissolved organics in municipal drinking water.
- FILTRASORBÂ® granular activated carbon - the industry standard for drinking water treatment.
- PEROXCARBÂ® granular activated carbon for hydrogen peroxide quenching in conjunction with UV-AOP systems.
- CENTAURÂ® granular activated carbon for targeted removal of iron and hydrogen sulfide from water.
- NSF-certified, CMR brand custom potable reactivation services for environmentally responsible and economical use of granular activated carbon.
Superior quality powdered activated carbons (PAC) for taste and odor removal.
Standardized, pre-engineered, "M-Series" adsorption equipment systems for potable water treatment.

To learn more about custom reactivation of activated carbon for drinking water treatment, click here.

Randy Holmes-Farley · Feb 7, 2015

Later on that same page, this company sells ion exchange technology for nitrate removal:

Ion Exchange Technology

Ion exchange technology is a cost effective process to treat municipal water contaminated by inorganic compounds. These compounds include but are not limited to:

Nitrate
Perchlorate
Hexavalent Chromium (Cr VI)
Color

Strict regulatory requirements are already in place for nitrate across the United States, while perchlorate is regulated in several US states. The U.S. Environmental Protection Agency intends to regulate perchlorate and hexavalent chromium.
Calgon Carbon’s Fixed Bed and Continuous ISEPÂ® technology systems are ideally suited to remove all of these compounds, allowing water utilities to comply with both today’s regulations, and tomorrow’s.
For more information, click here.

ReefHero · Feb 7, 2015

Awesome, just awesome info here Randy!
Thank you.
So, would I be wrong to say that because nitrate in seawater is so difficult to bind to medias as it would be in freshwater that we need to find alternative methods such as producing bacteria to absorb it instead?? Would the ion exchange nitrate removal for freshwater you mentioned earlier work with seawater??

Randy Holmes-Farley · Feb 7, 2015

You would not be wrong. Nitrate has no chemical handles with which any normal binder (short of the active site of an enzyme) can attach to. Consequently, the only way to easily bind it is through it's charge, but chloride is similarly charged and prevents nitrate from binding.

The ion exchange for nitrate cannot work in seawater for the same reason.

ReefHero · Feb 7, 2015

Ok so now I see why we are using bio pellets, carbon dosing, or refugiums in seawater to reduce our no3.....

ReefHero · Feb 7, 2015

I've been using Prodibio BioDigest and Bio Optim for the last few years and it has dropped my no3 to undetectable levels using a salifert test kit. Are you familiar with Prodibio? As far as I can see it is a way of producing bacteria just like carbon dosing and may very well be just basically carbon dosing lol.I will be sending my water away soon to Triton because after years of having an established reef and growing everything from frags I am curious to see what exactly is going on with some of my parameters.... Specifically I'd love to see if they can detect any no3 and I want to know levels of not normally tested parameters.