$\require{mhchem}$

Nitrification

Adapted from EPA Wastewater Management Fact Sheet

Nitrification refers to the conversion of ammonium $\ce{NH3}$ to nitrite $\ce{NO2-}$ and nitrate $\ce{NO3-}$. This process generally occurs in two steps orchestrated by different species of bacteria. This process requires oxygen and therefore only occurs in aerobic environments.

Step 1: $\ce{NH3 -> NO2-}$

Nitrosomonas, Nitrosococcus, and Nitrosospira bacteria, among others, convert ammonium to nitrite according to the following stochiometric equation:

\[\ce{NH3 + O2 -> NO2- + 3H+ + 2e-}\]

Step 2: $\ce{NO2- -> NO3-}$

Nitrobacter, Nitrospina, Nitrococcus, and Nitrospira bacteria, among others, convert nitrite to nitrate according to the following stochiometric equation:

\[\ce{NO2- + H2O -> NO3- + 2H+ + 2e-}\]

Denitrification

Adapted from EPA Wastewater Management Fact Sheet

Denitrification is the reduction of nitrites and nitrates to gas-form Nitrogen according to the following equations (Metcalf and Eddy, 1979):

Step 1:

\[\ce{6NO3- + 2CH3OH -> 6NO2- + 2CO2 + 4H2O}\]

Step 2:

\[\ce{6NO2- + 3CH3OH -> 3N2 + 3CO2 + 3H2O + 6OH-}\]

Which combine in the overall reaction scheme

\[\ce{6NO3- + 5CH3OH -> 5CO2 + 3N2 + 7H2O + 6OH-}\]

Denitrification does not require oxygen and typically occurs in an anoxic (oxygen-scarce) chamber of a wastewater treatment plant in order to cultivate denitryifying bacteria.