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Nitrification All or Nothing

When the AOB population is under stress, due to reduced dissolved oxygen concentration, low or high temperature, inhibition or other factors, the growth rate declines.

Because the kinetic constant for ammonia is so low (about one mg N/L) it is difficult to detect when the AOB population is declining.

For example, when there are no other constraints: by the time ammonia concentrations have changed from 0.2 to 2 mg N/L, the AOB population has declined by about 90%, and you are on the threshold of nitrification failure.

Nitrifying Microorganisms

  • Two step reaction – no known MO converts ammonia

to nitrate

  • AOB--ammonia to nitrite

  • NOB--nitrite to nitrate

  • AOB

consume

as

much

as

one

third

their

weight

of

ammonia per hour.

  • Low net yield is due to low energy yield, and the need to

use CO2 as the carbon than organic chemicals.

source

for

cellular

synthesis

rather

Ammonia Oxidizing Bacteria (AOB)

Nitrosomonas europaea

Nitrosococcus Nitrosospira Nitroslobus Nitrosovibrio

  • Convert ammonia to hydroxylamine, then nitrite

  • Key enzyme Ammonia Monooxygenase (AMO)

  • Substrate is Free Ammonia, NH3 (FA)

  • Product is Free Nitrous Acid (FNA)

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