Ozone and carbon

[Cory]

What does ozone do to activated carbon? Does the carbon last forever for the purpose of ozone? Does it need to be changed?

 

[Randy Holmes-Farley]

What does ozone do to activated carbon? Does the carbon last forever for the purpose of ozone? Does it need to be changed?

It generally will last a long. Longer than GAC for organic removal if there is sufficient ozone around because it keeps the GAC cleaner. I discuss the processes a bit here:

http://reefkeeping.com/issues/2006-04/rhf/index.php#15

 

[Cory]

It generally will last a long. Longer than GAC for organic removal if there is sufficient ozone around because it keeps the GAC cleaner. I discuss the processes a bit here:

http://reefkeeping.com/issues/2006-04/rhf/index.php#15

Yes ive read that, a good one! I was wondering if carbon neuralizes ozone forever, or it needs to be replaced?

 

[Randy Holmes-Farley]

Yes ive read that, a good one! I was wondering if carbon neuralizes ozone forever, or it needs to be replaced?

Forever is a long time, and the answer is no, it won't last forever, but it can last a long time.

I think the limiting factor in many cases is likely the GAC becoming clogged up with detritus before it loses its capacity to break down oxidation byproducts.

 

[Cory]

Forever is a long time, and the answer is no, it won't last forever, but it can last a long time.

I think the limiting factor in many cases is likely the GAC becoming clogged up with detritus before it loses its capacity to break down oxidation byproducts.

Ah okay. I read somewhere that when ozone comes in contact with carbon it makes Co2 and is thus neutralized. True? So it doesnt get adsorbed its broken down by gac?

 

[Randy Holmes-Farley]

Ah okay. I read somewhere that when ozone comes in contact with carbon it makes Co2 and is thus neutralized. True? So it doesnt get adsorbed its broken down by gac?

Some of the GAC may desorb as CO2, exposing more GAC below it, but that is not the primary process taking place.

 

[Cory]

Some of the GAC may desorb as CO2, exposing more GAC below it, but that is not the primary process taking place.

Ah okay. Whats the primary process put simply if you dont mind?

 

[Randy Holmes-Farley]

Ah okay. Whats the primary process put simply if you dont mind?

To break down the toxic byproducts of ozone reacting with seawater:

Toxicity of Ozone Produced Oxidants (OPOs)

Two sorts of toxicity studies of ozone produced oxidants (OPOs, such as bromate, hypobromous acid, etc.) are relevant to reef aquarists. The first involves the testing of seawater that has been exposed to ozone, and the second involves the testing of specific compounds dissolved in seawater that are known to form when using ozone. Most of the OPOs are unstable, and so have few or no specific toxicity studies. Bromate (BrO3-) is the notable exception, and its toxicity is examined in the next section.

Much of the study of OPOs stems from applications slightly different from aquaria, and such studies must be viewed in that light. Often they relate to aquaculture facilities, where ozone is used at high doses to sterilize the water. Other studies are done on the disinfection of wastewater using ozone, another high dose application. Bear in mind that OPOs in reef aquarium applications will be at a maximum of about 0.3 ppm in typical reaction chambers, and will be lower (hopefully, much lower) once the water passes over activated carbon (assuming it does) and finally enters the aquarium. The concentration of OPO is always given in terms of the weight of ozone that produces that amount of oxidant.

In terms of the toxicity of ozonated seawater itself, one group concluded that fish were relatively insensitive to OPOs:

"Ozonation of estuarine or marine waters can produce significant amount of bromate…Toxicity studies showed that the concentrations of bromate which theoretically could be formed in an ozonated discharge were not toxic to the early life stages of striped bass (Morone saxatilis) and juvenile spot (Leiostomus xanthurus)."50

Larvae are, in general, more sensitive to OPOs than are eggs,51 adults or juveniles.52 Japanese flounder eggs were found to be impacted by OPOs to the extent that 50% did not hatch after one minute of exposure to 2.2 ppm OPO. Larvae aged 3-15 days were killed to the extent of 50% in 24 hours at 0.02-0.05 ppm OPO. Larvae aged 44 days were killed to the extent of 50% in 24 hours at 0.15 ppm OPO. In this case, the larvae were shown to have damage to their branchial tissues.53

The eggs and larvae of Japanese whiting (Silago japonica) also have been tested for toxicity by OPOs. In this case, half of the eggs and larvae died in about 24 hours when exposed to 0.18 and 0.23 ppm OPOs, respectively.54

Certain microalgae are also relatively insensitive to OPOs (perhaps to the disappointment of many aquarists). The growth of the microalgae Tetraselmis chuii was found to be unaffected at levels up to 0.7 ppm.55 At 1 ppm, growth was impacted negatively.

Toxicity tests of OPOs on shrimp show them to be less sensitive than fish. Penaeus chinensis and Paralichthys olivaceus were found to live up to 48 hours at OPO concentrations of more than 1 ppm, while ******* halibut (fish) in the same study lived only three hours at 1 ppm and 48 hours at 0.13 ppm.56

As for other organisms, the damage to the American oyster (Crassostrea virginica) by OPOs varied with their age. Even for adults, fecal matter accumulation was reduced at OPO levels as low as 0.05 ppm.57

The effect of OPOs on rotifers (Brachionus plicatilis) has also been determined.58 No effect on survival was seen at less than 0.22 ppm OPO, but effects became significant above that level. The authors point out that bacteria and other pathogens can be killed at that level, so rotifer cultures can be used with that amount of continuous ozone to reduce bacterial contamination.

Are these levels of OPO toxicity important to reef aquarists? That is difficult to answer without knowing the levels that are attained in reef aquaria. In a typical ozone application in reef aquaria that might produce 0.1-0.3 ppm OPO in a reaction chamber, the levels are quite significant compared to potential toxicity to fish larvae and other organisms at as little as 0.02-0.05 ppm. After passing the reactor's effluent over activated carbon, the OPO concentrations should be much lower, but exactly how low is unclear and will vary considerably in different setups.

toxicity of excess bromate itself to marine organisms.60 One review article concluded:

"Bromate toxicity tests on marine animals indicate the levels of bromate produced by chlorination or ozonation of power plant cooling waters are not acutely toxic. The LC50ranged from 30 ppm bromate for Pacific oyster, Crassostrea gigas, larva to several hundred ppm for fish, shrimp and clams."9

One individual study showed that Pacific oysters (Crassostrea gigas) had abnormal larval development at bromate levels of 30-300 ppm.61,62 Fertilized eggs of the oyster Crassostrea virginicawere killed at 1 ppm.63 The clams Protothaca staminea (littleneck) and Macoma inquinata (bent-nosed) were killed by 880 ppm.64 The marine dinoflagellate Glenodinium halli showed changes in population growth at 16 ppm.65 The marine microalgae Isochrysis galbana showed changes in population growth at 8 ppm.65 The marine diatom (Skeletonema costatum) showed changes in population growth at 0.125 to 16 ppm.65 The marine diatom Thalassiosira pseudonana showed changes in population growth at 16 ppm.65 The salmon Oncorhynchus keta was killed at 500 ppm and the perch Cymatogaster aggregata at 880 ppm.64 Two shrimp (Pandalus danae and Neomysis awatschensis) were killed at 880 and 176 ppm, respectively.64

Are these levels of toxicity important to reef aquarists? That is difficult to answer without knowing the levels that are attained in typical reef aquaria. The one study in the literature of bromate in a seawater aquarium, described above, showed the accumulation of up to 0.6 ppm bromate, although that was an application in which ozone was used for disinfection, so it was used at high doses. That level is high enough, however, to cause toxicity to certain organisms, but not others. In a typical reef aquarium ozone application, the bromate in the aquarium water is likely to be much lower. How much lower will likely depend on the way it is used, especially the dose and whether it is passed over activated carbon before entering the aquarium. It may also depend on the other husbandry practices used in the aquarium, because some procedures (such as denitrification) may reduce bromate levels. In any case, the potential toxicity data for bromate support the practice of using activated carbon after ozone exposure.

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.69They 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.

 

[Holdbar7]

To break down the toxic byproducts of ozone reacting with seawater:

Toxicity of Ozone Produced Oxidants (OPOs)

Two sorts of toxicity studies of ozone produced oxidants (OPOs, such as bromate, hypobromous acid, etc.) are relevant to reef aquarists. The first involves the testing of seawater that has been exposed to ozone, and the second involves the testing of specific compounds dissolved in seawater that are known to form when using ozone. Most of the OPOs are unstable, and so have few or no specific toxicity studies. Bromate (BrO3-) is the notable exception, and its toxicity is examined in the next section.

Much of the study of OPOs stems from applications slightly different from aquaria, and such studies must be viewed in that light. Often they relate to aquaculture facilities, where ozone is used at high doses to sterilize the water. Other studies are done on the disinfection of wastewater using ozone, another high dose application. Bear in mind that OPOs in reef aquarium applications will be at a maximum of about 0.3 ppm in typical reaction chambers, and will be lower (hopefully, much lower) once the water passes over activated carbon (assuming it does) and finally enters the aquarium. The concentration of OPO is always given in terms of the weight of ozone that produces that amount of oxidant.

In terms of the toxicity of ozonated seawater itself, one group concluded that fish were relatively insensitive to OPOs:

"Ozonation of estuarine or marine waters can produce significant amount of bromate…Toxicity studies showed that the concentrations of bromate which theoretically could be formed in an ozonated discharge were not toxic to the early life stages of striped bass (Morone saxatilis) and juvenile spot (Leiostomus xanthurus)."50

Larvae are, in general, more sensitive to OPOs than are eggs,51 adults or juveniles.52 Japanese flounder eggs were found to be impacted by OPOs to the extent that 50% did not hatch after one minute of exposure to 2.2 ppm OPO. Larvae aged 3-15 days were killed to the extent of 50% in 24 hours at 0.02-0.05 ppm OPO. Larvae aged 44 days were killed to the extent of 50% in 24 hours at 0.15 ppm OPO. In this case, the larvae were shown to have damage to their branchial tissues.53

The eggs and larvae of Japanese whiting (Silago japonica) also have been tested for toxicity by OPOs. In this case, half of the eggs and larvae died in about 24 hours when exposed to 0.18 and 0.23 ppm OPOs, respectively.54

Certain microalgae are also relatively insensitive to OPOs (perhaps to the disappointment of many aquarists). The growth of the microalgae Tetraselmis chuii was found to be unaffected at levels up to 0.7 ppm.55 At 1 ppm, growth was impacted negatively.

Toxicity tests of OPOs on shrimp show them to be less sensitive than fish. Penaeus chinensis and Paralichthys olivaceus were found to live up to 48 hours at OPO concentrations of more than 1 ppm, while ******* halibut (fish) in the same study lived only three hours at 1 ppm and 48 hours at 0.13 ppm.56

As for other organisms, the damage to the American oyster (Crassostrea virginica) by OPOs varied with their age. Even for adults, fecal matter accumulation was reduced at OPO levels as low as 0.05 ppm.57

The effect of OPOs on rotifers (Brachionus plicatilis) has also been determined.58 No effect on survival was seen at less than 0.22 ppm OPO, but effects became significant above that level. The authors point out that bacteria and other pathogens can be killed at that level, so rotifer cultures can be used with that amount of continuous ozone to reduce bacterial contamination.

Are these levels of OPO toxicity important to reef aquarists? That is difficult to answer without knowing the levels that are attained in reef aquaria. In a typical ozone application in reef aquaria that might produce 0.1-0.3 ppm OPO in a reaction chamber, the levels are quite significant compared to potential toxicity to fish larvae and other organisms at as little as 0.02-0.05 ppm. After passing the reactor's effluent over activated carbon, the OPO concentrations should be much lower, but exactly how low is unclear and will vary considerably in different setups.

toxicity of excess bromate itself to marine organisms.60 One review article concluded:

"Bromate toxicity tests on marine animals indicate the levels of bromate produced by chlorination or ozonation of power plant cooling waters are not acutely toxic. The LC50ranged from 30 ppm bromate for Pacific oyster, Crassostrea gigas, larva to several hundred ppm for fish, shrimp and clams."9

One individual study showed that Pacific oysters (Crassostrea gigas) had abnormal larval development at bromate levels of 30-300 ppm.61,62 Fertilized eggs of the oyster Crassostrea virginicawere killed at 1 ppm.63 The clams Protothaca staminea (littleneck) and Macoma inquinata (bent-nosed) were killed by 880 ppm.64 The marine dinoflagellate Glenodinium halli showed changes in population growth at 16 ppm.65 The marine microalgae Isochrysis galbana showed changes in population growth at 8 ppm.65 The marine diatom (Skeletonema costatum) showed changes in population growth at 0.125 to 16 ppm.65 The marine diatom Thalassiosira pseudonana showed changes in population growth at 16 ppm.65 The salmon Oncorhynchus keta was killed at 500 ppm and the perch Cymatogaster aggregata at 880 ppm.64 Two shrimp (Pandalus danae and Neomysis awatschensis) were killed at 880 and 176 ppm, respectively.64

Are these levels of toxicity important to reef aquarists? That is difficult to answer without knowing the levels that are attained in typical reef aquaria. The one study in the literature of bromate in a seawater aquarium, described above, showed the accumulation of up to 0.6 ppm bromate, although that was an application in which ozone was used for disinfection, so it was used at high doses. That level is high enough, however, to cause toxicity to certain organisms, but not others. In a typical reef aquarium ozone application, the bromate in the aquarium water is likely to be much lower. How much lower will likely depend on the way it is used, especially the dose and whether it is passed over activated carbon before entering the aquarium. It may also depend on the other husbandry practices used in the aquarium, because some procedures (such as denitrification) may reduce bromate levels. In any case, the potential toxicity data for bromate support the practice of using activated carbon after ozone exposure.

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.69They 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.

I read the post above, but I didn't see where it says why carbon. I've read any porous surface for the o3 molecules to collide into would work. I'm curious as I have a chamber completely filled with rock rubble just after my skimmer/ return chamber and was thinking it would be sufficient at breaking down the o3

 

[Randy Holmes-Farley]

I read the post above, but I didn't see where it says why carbon. I've read any porous surface for the o3 molecules to collide into would work. I'm curious as I have a chamber completely filled with rock rubble just after my skimmer/ return chamber and was thinking it would be sufficient at breaking down the o3

While some other surfaces may work, the surface of GAC is catalytic in a way that others cannot be:

"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."

 

[Holdbar7]

Thank you!