Glutaraldehyde is not a carbon source

Solcielo lawrencia · Jun 17, 2015

Does glutaraldehyde really provide a carbon source for plants? Or does it work by killing the biofilm on plants which allows easier access to CO2?

- I read an article that stated that O2 levels are the same with or without adding glutaraldehyde. If it's a carbon source, then the rate of photosynthesis (by all photosynthesizing organisms, including algae) should be higher resulting in higher concentrations of O2. Further, higher concentrations should result in linear growth, but growth is nonlinear. This suggests that the increase in growth is due to other means.

Further evidence:

I've also observed that adding melaleuca oil (from API's Melafix) also increased growth at about the same rate as glut. Melaleuca oil (from the Tea Tree, Melaleuca alternifolia), is an antimicrobial chemical. Like glutaraldehyde, increasing the concentration does not result in increased rate of growth. If melaleuca inhibits the biofilm, then it allows the plants easier access to CO2 due to reducing competition for a very limited nutrient.

If true, then compounds that have antimicrobial effects, such as nutmeg oil, should also improve growth in submerged aquatic plants. And if glutaraldehyde isn't a carbon source, and works only by inhibiting and killing the biofilm on plants, then overdosing does more harm than good due to its biocidal effects.

Tom mentioned using C12 isotopes to track the carbon from glutaraldehyde. What were the results? This would prove or disprove this entire argument.

Marcel G · Jun 18, 2015

"Studies were conducted to determine the products of the aerobic and anaerobic metabolism of glutaraldehyde. Radiolabeled
glutaraldehyde was used in order to completely trace the degradation of the parent compound. Sacramento River water sediment

was used as the source of microorganisms to degrade the glutaraldehyde.The aerobic and anaerobic aquatic soil metabolism of

[1,5-14C]-glutaraldehyde was examined using a dose rate of 9.45 ppm based on active ingredient.The overall material balance

was determined at each point in order to ensure that no unaccountable losses of material occurred.

In the aerobic system, active glutaraldehyde had a half-life of approximately 10.6 hours and was completely metabolized after

48 hours. During this period, the radiolabeled glutaraldehyde was found to be converted first to glutaric acid, and then further

metabolized to carbon dioxide."

... In summary, the products of the aerobic and anaerobic metabolism of glutaraldehyde metabolism have been identified.

The major product of the aerobic metabolism of glutaraldehyde is carbon dioxide, while the major

product of anaerobic metabolism is 1,5-pentanediol.

Source: http://www.caiber.com/info/UCARCIDE%20CATALOGO.pdf

Solcielo lawrencia · Jun 22, 2015

How much CO2 is actually produced at suggested dosing levels? I speculate that it's probably so minute not to have any noticeable effect in CO2 concentration. I'm still not convinced it's main function is to provide CO2 as a constituent of it degradation. Killing algae and other microbes is probably what allows plants easier access to CO2. This would explain the 2-4x growth with glut VS 10-20x growth with CO2; i.e. 3-4ppm of equilibrium CO2 vs. 30-40ppm of injected CO2. If plants are outcompeted for that 3-4ppm of CO2, then that would explain the poor growth in non-CO2/glutaraldehyde tanks.

I can think of two ways to test this:

1. Apply an algaecide other than glutaraldehyde and see if the same effects can be observed.

2. Oxidize algae by adding high concentrations of O2.

Marcel G · Jun 22, 2015

Let me give you a qualified guess:

In the 112L (30G) tank with a dimensions of 80x35x40cm (32x14x16") your plants can increase in biomass by about 1 gram of fresh weight per dm2 = 10x10cm (under "normal" conditions in an average planted tank). So you get about 30 grams of fresh weight per week = 4.3 g/day. With 45% of carbon in the dry matter you get about 45 mg C per 1g of fresh weight (1g FW = 0.1g DM), which is an equivalent of 165 mg CO2. So for producing 30 gram of FW the plants have to uptake about 5 grams of CO2 (165mg * 30g) per week. That's 0.7 g = 700 mg CO2 per day.

The formula of glutaraldehyde is C5H8O2. In 5 ml of 1.5% solution of glutaraldehyde (= recommended dose for 100L tank) is about 0.075 g of pure glutaraldehyde (C5H8O2). That's about 0.045 g of pure carbon ©, which is an equivalent of 0.165 g = 165 mg CO2 per day.

Result: 700 vs. 165 mg CO2 per day => 700/165 = approx. 4:1

So using the liquid carbon we are theoretically able to meet about 1/4 of the plant needs in an average planted tank. In other words ... we are able to produce about 1/4 of the total biomass of an average planted tank supplied by gaseous CO2.

This calculation assumes that all the supplied glutaraldehyde is uptaken and utilized by plants (no loss, no degradation).

One little note:

PEDERSEN, Ole; CHRISTENSEN, Claus; ANDERSEN, Troels. CO2, Light, and Growth of Aquatic Plants. Planted Aquaria, Spring 2001.

Look at results of their experiment with Riccia:

Do you see any substantial difference between 7 ppm vs. 35 ppm CO2?

So even if we add a couple of ppm (CO2) by using liquid carbon, I think that the difference (compared to gaseous CO2) may not be as big as one would expect.

Johnk · Jul 1, 2015

Or do the high co2 levels we inject inhibit algal growth and do the same to the biofilm as other algaecides? This might explain why low and fluctuating CO2 levels work against us. The amount of CO2 required for plant growth might be quite modest. Chlorella microalgae are reported to be inhibited by CO2 greater than 5%. Another paper suggests some blue green algae are killed when the acidification caused by elevated CO2 levels falls below 6.5. ( = pH drop rather than actual pH? )

If true it would be a nicer explanation than plants outcompeting for available CO2. Are we just acid washing our plant leaves so they absorb what they need more easily?

Tom Barr · Jul 2, 2015

You are using the fresh/dry weight of Riccia total Carbon for the CO2 gas enrichment.

Then comparing it to the Glut and assuming that the entire Glut added is being used up as plant biomass(as you note).

Those are two very different things and not comparable as presented.

We add about 2 ppm of Glut as recommended by the label, metabolism yields about 4 ppm of CO2 if there's complete aerobic metabolism and this assumes that the plant gets it all.

4 ppm of added CO2 is not much per day(it's not maintained all day at that concentration in other words). Adding CO2 gas, we add a LOT more CO2.

You still get growth(same for no CO2 sources other than surface exchange with the air), but there's just not enough CO2 produced to offer much growth. Some CO2 is going to be lost also to degassing and bacterial attack.

More likely, the periphyton is being removed with the glut as an algicide, this allows better exchange across the leaf surface.

Some CO2 is used certainly by the plants, but there's just not enough to make a large dent in growth.

Regarding varying CO2 or fert levels: enzyme kinetics explains the problems there, stability works better than variation.

Another potential: the bacteria communities are shifted to favor more plant friendly periphyton communities using Glut.

Radio labeled Glut is about 10,000$ for a 500ml amount of 50%. then you have to measure it and have the certification.

We had this at the lab(certification), but I did not have any $ or funding for it, I asked Seachem some, but they are not going to spend the $ for it, and as far as an aquatic weed killer, it's a poor candidate, so no weed professor would take that on for obvious reasons. Interesting, but not a good investment. Greg Morin(SeaChem) and I talked about this years ago. They had little reason to do it also.

It's a good way to see what goes what goes where.

Marcel G · Jul 2, 2015

Johnk said:
Chlorella microalgae are reported to be inhibited by CO2 greater than 5%. Another paper suggests some blue green algae are killed when the acidification caused by elevated CO2 levels falls below 6.5.

I'm not sure the equation is that simple, but if we use the rule of three ...

0,04% CO2 in air = 0,6 ppm CO2 in water (= equilibrium state)

5,00% CO2 in air = 75 ppm CO2 in water

So at 5% CO2 in air you would get about 75 ppm CO2 in your aquarium which is way too high.

PS: I have read some articles about toxicity of CO2 for algae, and most algae species tested have this value somewhere around 15% which would give you more than 200 ppm in your tank. So I think that we can not inhibit algae by CO2 itself ... given we don't want to kill all our critters at the same time. Low pH seem to have much stronger inhibitory effect on algae. As you said, in pH under 6.5 some algae and cyanobacteria seems to have problems. Don't forget also that at lower pH most nutrients are better digestable/available. So the side effect of lower pH is better availability of nutrients. All in all, it's not just one factor which is in play here.

Marcel G · Jul 2, 2015

Tom Barr said:
Radio labeled Glut is about 10,000$ for a 500ml amount of 50%. then you have to measure it and have the certification.

There is much simpler way how to test the effects of glutaraldehyde vs. CO2 on plant growth.

You can set up several small tanks where you'll have same conditions except the carbon concentration.

You can add gas CO2 into tank #1 and #2, and glutaraldehyde into tank #3 and #4. You can repeat this test with different CO2/carbon concentrations also to see what difference it will make.

Then you can put few samples of the same plant into each tank, and watch their growth rates.

For our purposes, this experiment is much easier to do ... and much cheaper.

Glutaraldehyde is not a carbon source

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