Nitrification equation

[Charles Silva]

Hello

Please can someone with chemistry/biology background help me understand the meaning of 2e- and NH2OH at the nitrification equation ?

The equation result is also H+ (lowering the pH and consuming alkalinity) but in practical terms is this alkalinity reduction significant in our aquariums ?

The nitrification is done by chemolithoautotroph bacteria meaning that they get their energy from inorganic source and the carbon from environment CO2. Where is the CO2 in the nitrification equation ? Or the bacteria use CO2 and other inorganic "food" to produce mass and the nitrification occurs inside the bacteria ?

thanks
Charles Silva

 

[Azedenkae]

You are correct, the CO2 is not involved in this equation. It is used for growth - i.e. that's where the carbon for building... everything comes from. Though I am not entirely sure if nitrifiers use CO2 or some other inorganic substrate. I mean probably CO2, I just have not actually had a look myself.

Interestingly enough, Wikipedia's article on nitrification is quite informative in understanding the process well: https://en.wikipedia.org/wiki/Nitrification.

But anyways, I also like to provide my own descriptions.

NH2OH is hydroxylamine. The theory is that ammonia oxidation is actually not a one step process, but rather two, and requires two genes - at least in bacteria: amoA and hao, required for the conversion of ammonia to hydroxylamine, then nitrite.

The 2e- (or just e-) are the electrons produced from the oxidation process, which is then transferred to an electron-carrier in the electron transport chain, and then that transfers the electrons to a terminal electron acceptor, which is conventionally oxygen.

The protons produced can lower pH, but bare in mind, when electrons are transferred to oxygen as the terminal electron acceptor, protons are also used then, so that ultimately we get water.

Here are the two halves of aerobic ammonia oxidation:
https://metacyc.org/META/NEW-IMAGE?type=PATHWAY&object=AMMOXID-PWYhttps://metacyc.org/META/NEW-IMAGE?type=REACTION&object=CYTOCHROME-C-OXIDASE-RXN

 

[Randy Holmes-Farley Verified Community Expert]

If nitrate is accumulating, it will deplete alk. If it is not accumulating, there is no net alk loss.

Here are some equations from my articles
Overall
NH3 + 2O2 —> NO3- + H+ + H2O

Stepwise
NH4+ + 3/2 O2 —> NO2- + 2H+ + H2O

NO2- + ½ O2 —> NO3-

 

[taricha]

The equations in the first post that don't balance charges left and right hurt my feelings. I much prefer Randy's charge-balanced accounting.

 

[brandon429]

question on nitrate accumulating vs being produced

so if nitrate is produced in the reaction doesn't that lower the alk, the steps it took to get to nitrate, even if denitrification scrubs it out of the system after? I didn't think there has to be residual/accumulating nitrate in the system to lower alk I thought the initial production machinery that made it in the metabolic pathway used the alk?

 

[nereefpat]

question on nitrate accumulating vs being produced

so if nitrate is produced in the reaction doesn't that lower the alk, the steps it took to get to nitrate, even if denitrification scrubs it out of the system after? I didn't think there has to be residual/accumulating nitrate in the system to lower alk I thought the initial production machinery that made it in the metabolic pathway used the alk?

If nitrate is produced in the tank and then is denitrified to Nitrogen gas, then the net on alkalinity is zero.

If nitrate accumulates, alk is being consumed.
If you dose nitrate, you will be adding alk, as long as the nitrate is denitrified.

 

[Randy Holmes-Farley Verified Community Expert]

question on nitrate accumulating vs being produced

so if nitrate is produced in the reaction doesn't that lower the alk, the steps it took to get to nitrate, even if denitrification scrubs it out of the system after? I didn't think there has to be residual/accumulating nitrate in the system to lower alk I thought the initial production machinery that made it in the metabolic pathway used the alk?

Denitrification adds back exactly the same amount of alk that was depleted to produce the nitrate.

 

[Dan_P]

The equations in the first post that don't balance charges left and right hurt my feelings. I much prefer Randy's charge-balanced accounting.

If you got more sleep you wouldn’t be so sensitive :)