Nitrate Consumption Rates And Stoichiometry For Organic Carbon Dosing

[Randy Holmes-Farley]

Try this.

I set the doses of acetic acid and ethanol to cause an equi-molar consumption of nitrate. As a first approximation, the energy requirement for bacteria growth is the same regardless of the carbon source. Since acetic acid has a lower energy content than ethanol, a great amount of acetic acid needs to be oxidized. Basing energy content only on the number of oxygens needed, I would say ethanol has 1.5 times more energy content than acetic acid, and therefore, only 2/3 the amount of ethanol is needed compared to acetic acid to supply the same energy. Directionally, this is what I observed but my calculated ratio of ethanol oxidized vs acetic acid is only about 1/3.

I could readily accept almost any result in the relative nitrate consumption capability of ethanol vs acetic acid, since it reflects not only how much energy is in each (we know that), but how efficient all of these organisms might be at converting that available energy into ATP (we do not know that, and it may involve energy needed to take up the molecules, not just how readily they can convert them internally).

What I don't understand is the O2 consumption difference. From the equations you showed, ethanol uses 3 O2 per molecule while acetic acid uses only 2.

maybe I'm not understanding what 0.5x and 0.33x means, but I took it as a mole ratio.

Thus,
ethanol should consume 0.33 x 3 = 1 unit of O2
acetic acid should consume 0.5 x 2 = 1 unit of O2

But you showed significantly more O2 consumed with acetic acid.

My question is why.

 

[BeanAnimal]

Could there be another compound being formed during the consumption that is binding oxygen, but not being tested for?


I figured that if I asked a chemistry sounding question, I would be able to stay and fit in...

 

[Randy Holmes-Farley]

Could there be another compound being formed during the consumption that is binding oxygen, but not being tested for?


I figured that if I asked a chemistry sounding question, I would be able to stay and fit in...

There's no stable molecule that has a higher oxygen to carbon ratio than CO2. To use more O2 than formation of CO2, that would be needed. One could invoke speculative ideas like the presence of acetate spurs organisms to oxidize other molecules in their stores (think drinking vinegar making one burn fat), but I've never heard of a process like that.

 

[sixty_reefer]

@Dan_P just talking about his bacterias favorite Redfield Ratios.
Lol. Sorry. couldn't help it.

Have you calculated the CNP ratio in ethanol results from this test? Not far from it

 

[Randy Holmes-Farley]

Have you calculated the CNP ratio in ethanol results from this test? Not far from it

What CNP ratio are you talking about? And not far from what?

 

[Dan_P]

I could readily accept almost any result in the relative nitrate consumption capability of ethanol vs acetic acid, since it reflects not only how much energy is in each (we know that), but how efficient all of these organisms might be at converting that available energy into ATP (we do not know that, and it may involve energy needed to take up the molecules, not just how readily they can convert them internally).

OK, no debate here. On a per molecule basis, dosed ethanol results in more nitrate being removed from solution than with acetate. Also, more phosphate is consumed with ethanol dosing. Interestingly, the consumption ratio of phosphate:nitrate is similar for both ethanol and acetic aci

What I don't understand is the O2 consumption difference. From the equations you showed, ethanol uses 3 O2 per molecule while acetic acid uses only 2.

maybe I'm not understanding what 0.5x and 0.33x means, but I took it as a mole ratio.

Sorry about the ambiguity. The numbers refer to the relative size of the dose of equi-molar solutions of acetic acid (vinegar) and ethanol. So, yes, treating them as mole ratios is correct.

Thus,
ethanol should consume 0.33 x 3 = 1 unit of O2
acetic acid should consume 0.5 x 2 = 1 unit of O2

One additional statement is needed here for completeness, “if the entire dose of ethanol and acetic acid are oxidized”. Should we assume the carbon doses are completely oxidized? No, because it is widely known that creating biomass is the outcome of feeding heterotrophic bacteria carbon and nitrogen. This means the carbon is divided between energy generation and biomass generation.

But you showed significantly more O2 consumed with acetic acid.

My question is why.

Acetic acid provides less energy to the cell than ethanol. To consume the same amount of nitrate (it was) and presumably make the same amount of biomass as is achieved with ethanol, more acetic acid needs to be oxidized. Interestingly, the “organic residual”, the carbon remaining from the dose that is not oxidized and can be used for biomass production, is the same for ethanol and acetic acid.

 

[sixty_reefer]

What CNP ratio are you talking about? And not far from what?

It could be just a coincidence but it seems that the bacteria in this test is assimilating CNP on a ratio very close to Redfield.

 

[Dan_P]

Could there be another compound being formed during the consumption that is binding oxygen, but not being tested for?


I figured that if I asked a chemistry sounding question, I would be able to stay and fit in...

Lookin’ good!

 

[Randy Holmes-Farley]

It could be just a coincidence but it seems that the bacteria in this test is assimilating CNP on a ratio very close to Redfield.

It would be reasonable for growth, but how did you get a C value for that?

 

[Randy Holmes-Farley]

Acetic acid provides less energy to the cell than ethanol. To consume the same amount of nitrate (it was) and presumably make the same amount of biomass as is achieved with ethanol, more acetic acid needs to be oxidized. Interestingly, the “organic residual”, the carbon remaining from the dose that is not oxidized and can be used for biomass production, is the same for ethanol and acetic

What fractions did you calculate were converted to CO2 in each case?

 

[sixty_reefer]

It would be reasonable for growth, but how did you get a C value for that?

I’ve used Dan total organic, everything in this chart is already in moles, I believe that there is no further conversion needed.

Ethanols C 0.077/0.00063=122 N 0.0127/0.00063=20 P 0.00063/0.00063=1

122:20:1 CNP

Vinegar C 0.116/0.00105=110 N 0.0119/0.00105=11 P 0.00105/0.00105=1

110:11:1 CNP

As I mentioned earlier it could be just a coincidence that the usage ratio becomes within range of Redfield although this has been my past experience as well.

It was pointed out that a average of a ratio of 10:1 N P was observed in ppm that translates to 16:1 in moles.

 

[Dan_P]

What fractions did you calculate were converted to CO2 in each case?

I did not calculate this, but I guess if I did, it would be estimated from the oxidation equations, two CO2 for every acetate or ethanol molecule oxidized.

 

[Randy Holmes-Farley]

I did not calculate this, but I guess if I did, it would be estimated from the oxidation equations, two CO2 for every acetate or ethanol molecule oxidized.

How then did you make this conclusion?

Interestingly, the “organic residual”, the carbon remaining from the dose that is not oxidized and can be used for biomass production, is the same for ethanol and acetic acid.

 

[Randy Holmes-Farley]

I’ve used Dan total organic, everything in this chart is already in moles, I believe that there is no further conversion needed.

Ethanols C 0.077/0.00063=122 N 0.0127/0.00063=20 P 0.00063/0.00063=1

122:20:1 CNP

Vinegar C 0.116/0.00105=110 N 0.0119/0.00105=11 P 0.00105/0.00105=1

110:11:1 CNP

As I mentioned earlier it could be just a coincidence that the usage ratio becomes within range of Redfield although this has been my past experience as well.

It was pointed out that a average of a ratio of 10:1 N P was observed in ppm that translates to 16:1 in moles.

Ok, so that assumes that all of the C in those organics ended up as tissue and none as CO2?

 

[Dan_P]

How then did you make this conclusion?

Interestingly, the “organic residual”, the carbon remaining from the dose that is not oxidized and can be used for biomass production, is the same for ethanol and acetic acid.

Pure math.

The mM of acetic acid or ethanol added to the water minus the mM of the dose oxidized which was calculated from the oxidation equations is the residual carbon, aka, left over dose. Seems reasonable that it was consumed. If it wasn’t consumed, we would have to explain why only some of the organic dose was oxidized (based on the amount of oxygen consumed) and nitrate consumption stopped. Make sense?

 

[sixty_reefer]

Ok, so that assumes that all of the C in those organics ended up as tissue and none as CO2?

Yeah, I’ve also assumed that phosphate and nitrate didn’t had any testing errors.
It shouldn’t come as a surprise that it would be within range.
I’ve read in one of your articles on carbon dosing that you have speculated a 16:1 usage ratio and I’ve seen many other manufacturers of bio pellets to back that same usage ratio.

 

[Curiousbranching]

Have you conducted this experiment with methanol? I'm really curious to know whether methanol is useful for providing carbon to microorganisms because a certain brand claims that their carbon product contains a small amount of methanol.

 

[Randy Holmes-Farley]

Pure math.

The mM of acetic acid or ethanol added to the water minus the mM of the dose oxidized which was calculated from the oxidation equations is the residual carbon, aka, left over dose. Seems reasonable that it was consumed. If it wasn’t consumed, we would have to explain why only some of the organic dose was oxidized (based on the amount of oxygen consumed) and nitrate consumption stopped. Make sense?

Yes. That’s what I was asking about a few posts above, but maybe my use of the term fraction oxidized was confusing.

 

[Randy Holmes-Farley]

Have you conducted this experiment with methanol? I'm really curious to know whether methanol is useful for providing carbon to microorganisms because a certain brand claims that their carbon product contains a small amount of methanol.

It will be. NOPOX contains methanol, but I expect it is there to make the ethanol untaxed and undrinkable (denatured), not because it provides a benefit that the ethanol and acetic acid do not. Same for the isopropanol in NOPOX.

 

[Dan_P]

Have you conducted this experiment with methanol? I'm really curious to know whether methanol is useful for providing carbon to microorganisms because a certain brand claims that their carbon product contains a small amount of methanol.

I have not looked at methanol but it is used in sewage treatment as a carbon source. Probably works like ethanol except you need to dose 2 times as much.