UV vs GAC post Ozone

[GARRIGA]

Seems UV can dissipate ozone and products exist that combine ozone using a reactor. Therefore if using UV post ozone with enough distance allowing ozone to perform its function does one still need GAC other than to perform other functions like pulling items not affected by either ozone or UV? Wanting to confirm UV fully neutralizes ozone. I believe it does with hydrogen peroxide but ozone in this manner seems simpler and safer to me.

Illustration of combo I’m considering.

 

[Randy Holmes-Farley]

I do not know what will happen in a practical situation, but the chemistry of ozone is far more complicated than it may seem. Ozone quickly reacts with seawater constituents to make other highly oxidizing products (called OPO's, or ozone produced oxidants) and these are broken down by GAC. I do not know what they do under UV, but they can be toxic.

I described these processes here:

Ozone and the Reef Aquarium, Part 1: Chemistry and Biochemistry by Randy Holmes-Farley - Reefkeeping.com

from it:

The Effect of Activated Carbon on Ozone Produced Oxidants
In order to reduce ozone's potential toxicity, aquarists typically try to reduce the OPOs in the effluent coming from the ozone reaction chamber. There are a variety of ways to accomplish that, but by far the most commonly used is passing the water over activated carbon (GAC).

In a previous article on how reverse osmosis/deionizing water purification systems work on tap water, Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria, I showed how hypochlorite reacted with activated carbon. Bromate and hypobromite are expected to react similarly. The reactions within the activated carbon that break down these compounds rely on having enough active surface area and time for these catalytic reactions to take place. How effective that is in a high flow application such as a skimmer's effluent is unclear. It is effective in reverse osmosis/deionization (RO/DI) applications because the flow is low and the carbon's surface area is very high.

When bromate and hypobromite interact with the activated carbon's surface, they are broken down into bromide ion (Br-) and oxygen as shown below for bromate, where C* stands for the activated carbon and CO* stands for the activated carbon with an attached oxygen atom.

BrOH + C* --> Br- + CO* + H+

Some of the oxidized activated carbon remains, and some breaks down to produce oxygen (O2):

2CO* --> 2C* + O2

Some of the CO* can also break down to CO2 (carbon dioxide) in a noncatalytic breakdown of the OPO, but that is typically a small fraction of the total. None of these products of reactions are of significant concern to reef aquarists.

The big question for each aquarist is how effective is the GAC that is being used? As is true for many things examined in this field, the studies often have been done at high OPO concentrations relating to disinfection, and are usually in freshwater. In one patent application, a GAC bed was used to reduce the OPO in the water passing through it from 1.1 ppm to less than 0.2 ppm.66 Another group showed that completely removing the bromate required a contact time with the activated carbon of more than 15 minutes.67 In this test and in many others that have been published, older activated carbon was less effective than new activated carbon. The reason is that organics occupy portions of the GAC's surface where bromate and other OPOs are broken down.

A second group studying bromate in drinking water showed that GAC could remove 78-96% of bromate.68 They found that contact time and age of the carbon were important parameters affecting the removal percentage.

Besides activated carbon, there are other potential ways to remove OPO's. In one patent application, researchers have shown that the water used in aquaculture applications can be treated with ozone, and then with reducing agents that react with and destroy these agents, thereby reducing its toxicity.69 They recommend sulfite, bisulfite, metabisulfite or thiosulfate for that purpose, but it clearly is not simple to accomplish this automatically in a reef aquarium.

Does GAC or any other of these methods work well enough for reef aquarists to use ozone without undesirable side effects? The answer likely depends on the care which is used in the GAC treatment, and the aquarist's tolerance for OPOs to pass into the aquarium. The answer is likely not well enough when using the highest doses typically used by aquarists and the lowest tolerance for OPOs (that is, the lowest levels likely to cause ANY undesirable effects). Because it is not easy for most aquarists to measure low concentrations of OPOs, the most prudent course of action (aside from not using ozone) is to pass the ozonated aquarium water over as much GAC as possible before letting it re-enter the aquarium.

 

[GARRIGA]

Was the OPO I had read from you why I ask. Not clear on exactly what those are. Would ICP show them so one can determine if being produced by what I’m prescribing?

 

[Randy Holmes-Farley]

Was the OPO I had read from you why I ask. Not clear on exactly what those are. Would ICP show them so one can determine if being produced by what I’m prescribing?

Nope. the bromine versions just show up like bromide, chloride versions like chloride, etc.

I describe them in other sections of the article.

 

[GARRIGA]

Any of these issues using hydrogen peroxide as I believe UV will dissipate that under the same application?

 

[taricha]

I wonder if ORP meter might tell you about the OPOs presence or destruction. Seen people running Ozone talk about how their ORP dropped when they brought UV online due to the UV destroying the ozone that would otherwise stick around in the water longer.

 

[Randy Holmes-Farley]

I don’t know if ORP directly responds to either ozone or OPO’s directly as opposed to the various redox active trace elements present.

 

[Randy Holmes-Farley]

FWIW, a kit can detect them:

Water analysis​

Ozone-produced oxidants (OPO) were determined spectrophotometrically several times a day using the colorimetric N,N-diethyl-p-phenylenediamine (DPD) method (DPD Total chlorine powder pillows, Hach) as recommended for measurements of total residual oxidants (TRO) in seawater (Buchan et al., 2005).

https://www.sciencedirect.com/science/article/pii/S2352513423002764

 

[GARRIGA]

I wonder if ORP meter might tell you about the OPOs presence or destruction. Seen people running Ozone talk about how their ORP dropped when they brought UV online due to the UV destroying the ozone that would otherwise stick around in the water longer.

Got my HM Digital ORP probe today for exactly what you mentioned although to test hydrogen peroxide as I’ve heard ORP drops during application.

Been doing more research and UVC not only decomposes hydrogen peroxide but it also breaks down ozone assuming that paper is accurate. Interesting how all this works. 253nm knocks these items down yet 185nm creates ozone.

I’m not a scientist yet find all this fascinating and just trying to apply best to solve issues such as pathogens and decomposing matter.

 

[GARRIGA]

FWIW, a kit can detect them:

Water analysis​

Ozone-produced oxidants (OPO) were determined spectrophotometrically several times a day using the colorimetric N,N-diethyl-p-phenylenediamine (DPD) method (DPD Total chlorine powder pillows, Hach) as recommended for measurements of total residual oxidants (TRO) in seawater (Buchan et al., 2005).

https://www.sciencedirect.com/science/article/pii/S2352513423002764

As it relates to bromine. Finding Bromide in ICP or lack of wouldn’t suggest that particular OPO might be present or guaranteed it’s absent?

 

[Randy Holmes-Farley]

As it relates to bromine. Finding Bromide in ICP or lack of wouldn’t suggest that particular OPO might be present or guaranteed it’s absent?

No.

Ozone converts bromide into more oxidized forms, but the total bromine element concentration is unchanged:

Halogens

When ozone is applied in seawater in concentrations higher than are naturally present, a larger variety of chemical reactions take place. Chief among these is oxidation of bromide to hypobromite:6,7

O3 + Br- --> BrO- + O2

BrO- + H2O --> BrOH + OH-

The first reaction is very fast, and the half life of unreacted ozone in water with a lot of bromide (such as seawater) is on the order of a few seconds.8 Because hypobromous acid's pKa (in freshwater) is about 9, it is primarily in the protonated (uncharged form) in seawater, but a significant amount of BrO- is also present.3 The hypobromous acid is itself a strong oxidizer and can rapidly oxidize other organic or inorganic materials.4

The hypobromous acid can also react in a variety of ways (including disproportionation and additional oxidation with ozone) to form bromate:

BrOH --> --> --> BrO3-

The hypobromous acid can also be catalytically broken down by ozone to return to bromide:

BrOH + O3 --> 2O2 + Br- + H+

About extensive ozonation of seawater, one group concluded:

"Ozonization of seawater oxidizes bromide ion to Br (hypobromous acid and hypobromite ion) and then to bromate. If seawater is ozonized for >60 min, essentially all bromide is converted to bromate."9

That level of ozonation, however, is far more than would take place in a reef aquarium. The various reactions leading to bromine-containing byproducts of water's ozonation have been extensively studied (especially in the context of disinfecting fresh drinking water that contains bromide). Nevertheless, it is a complex problem. One recent review3 stated:

"Because bromate formation during ozonation of bromide-containing waters is a highly non-linear process, kinetic modeling has been applied to improve mechanistic understanding and to predict bromate formation. The full model consists of more than 50 coupled kinetic equations which can be solved simultaneously with a computer code…"

and then went on to say,

"the predictive capabilities of such models for the ozonation of any water should not be overestimated."

Well, we won't try to calculate what happens in reef aquaria, but we will conclude that bromate and hypobromite may be significant.

Bromate is typically the longest lived after ozonation of bromide-containing water. It is, in fact, one of the biggest concerns with ozonation as a purification method for drinking water, because bromate is a suspected carcinogen. For this reason, the US EPA limits it to only 10 ppb in drinking water. So in considering the properties of the treated seawater in aquaria, both BrOH/BrO- and BrO3- must be considered.

There is at least one study in the literature of bromate in a seawater aquarium.10 Here the ozone was used for disinfection, so the doses used may be higher than many aquarists employ. I also do not know whether or how effectively they treated the post ozone water with activated carbon. Nevertheless, the bromate levels in the Living Seas exhibit at Walt Disney World's Epcot Center were tracked. The researchers studying this display found that bromate had risen to about 0.6 ppm (with nitrate at about 600 ppm). After adding a batch denitrifying system, the bromate and nitrate concentrations began to drop, suggesting a sink for bromate that might well exist in many reef aquaria as well (that is, in systems or locations where denitrification takes place).

The same reactive pathways that lead hypobromous acid to bromate will take hypoiodous acid to iodate.

IOH --> --> --> IO3-

In the ocean, iodine's predominate form is iodate (IO3-) with a smaller but significant fraction of iodide (I-). These two forms' bioavailability to macroalgae and other organisms varies from species to species, but iodide is often more bioavailable than iodate. Regardless, the use of ozone will likely skew the fraction of total iodine toward iodate and away from iodide. That may or may not be important for reef aquarists, because the importance of iodine's availability from the water column to organisms kept in reef aquaria is undemonstrated, but it may have strong implications if test kits are used detect some species and not others.

This concern was studied by one group in the Smithsonian National Zoological Park's Department of Animal Health.11 It claimed that fish need iodide in the water column in the form of iodide to make the hormone thyroxine. Regardless of whether that is true or not (that is, whether fish need iodine in the water or whether they can get it from food), they showed that seawater's ozonation to an ORP of 400 mV (equivalent, they claim, to the level attained by skimmer driven use of ozone) reduced the iodide concentration by more than half. Ozonation also decreased the concentration of organoiodine compounds, and raised iodate levels. In the aquarium itself, iodide and organoiodine compounds were not detectable when using ozone. They go on to suggest that iodide supplements might be beneficial in cases when ozone is used. Therefore the conclusion that "iodine is an unnecessary additive for reef aquaria," when that conclusion is based on success in aquaria not using ozone, may not extend to aquaria that heavily employ ozone.

As long as bromide remains in the seawater, the equivalent reaction of ozone with chloride

O3 + Cl- --> ClO- + O2

is unlikely to be significant as it is much slower than reaction with bromide. The small amount of ClO- that may form can react with bromide to form BrO-.3,6,8

 

[GARRIGA]

There is at least one study in the literature of bromate in a seawater aquarium.10 Here the ozone was used for disinfection, so the doses used may be higher than many aquarists employ. I also do not know whether or how effectively they treated the post ozone water with activated carbon. Nevertheless, the bromate levels in the Living Seas exhibit at Walt Disney World's Epcot Center were tracked. The researchers studying this display found that bromate had risen to about 0.6 ppm (with nitrate at about 600 ppm). After adding a batch denitrifying system, the bromate and nitrate concentrations began to drop, suggesting a sink for bromate that might well exist in many reef aquaria as well (that is, in systems or locations where denitrification takes place).

If denitrification is a plausible solution then can carbon dosing solve this issue in place of actual carbon such as GAC?

 

[Randy Holmes-Farley]

If denitrification is a plausible solution then can carbon dosing solve this issue in place of actual carbon such as GAC?

No. A batch denitrifier deoxygenates all the water in the batch. You would not want to do that to the whole aquarium, and lowering opos only down in sand isn’t very useful.

 

[GARRIGA]

No. A batch denitrifier deoxygenates all the water in the batch. You would not want to do that to the whole aquarium, and lowering opos only down in sand isn’t very useful.

Then GAC the only solution or just don't do ozone

 

[Randy Holmes-Farley]

That's my recommendation, unless the amount added is quite low (which may be fine).

 

[michealprater]

Not sure of the scientific reason, but I run ozone and UV. However, since adding UV, my ozone never kicks on due to the ORP skyrocketing to levels in the 480s. I do not run GAC.

 

[taricha]

1) GAC is known to work as Randy has laid out.
2) you could use the total chlorine test packets from hach or hanna that were mentioned to verify that they are destroyed. The packets are easy - I've used them.
3) You might be able to destroy the OPOs with UV, but you'd need to do the tests like in 2) to be sure. It might not work.

So GAC seems really cheap, easy, and reliable in that context.

 

[GARRIGA]

Not sure of the scientific reason, but I run ozone and UV. However, since adding UV, my ozone never kicks on due to the ORP skyrocketing to levels in the 480s. I do not run GAC.

that’s interesting

 

[GARRIGA]

1) GAC is known to work as Randy has laid out.
2) you could use the total chlorine test packets from hach or hanna that were mentioned to verify that they are destroyed. The packets are easy - I've used them.
3) You might be able to destroy the OPOs with UV, but you'd need to do the tests like in 2) to be sure. It might not work.

So GAC seems really cheap, easy, and reliable in that context.

Was thinking about the total chlorine test strips from LaMotte. I’ve used those in the past in my FW tanks. Just to be clear because the science often goes over my head. The chlorine strips would also detect other OPO? I’m sure that wasn’t impressed on me or I just read over it or misunderstood.

 

[michealprater]

that’s interesting

I need more bioload lol.