Nitrification
Nitrification is the first step of the nitrogen removal process, involving the conversion of Ammonium (NH4+), the form in which nitrogen is commonly present in raw wastewater, to nitrite (NO₂⁻) then nitrate (NO3-).
Nitrification is an aerobic process (requires Oxygen). This process is carried out in two stages by two groups of autotrophic bacteria.
In the first stage, ammonia-oxidizing bacteria (AOB), called Nitrosomonas, convert ammonium (NH4+) to nitrite (NO₂⁻).
Nitrosomonas: Converts ammonium (NH4+) to nitrite (NO₂⁻). (Nitrosomonas reproduce by binary fission)
In the second stage, nitrite-oxidizing bacteria (NOB), called Nitrobacter, convert nitrite to nitrate.
Nitrobacter: Oxidizes nitrite (NO₂⁻) to nitrate (NO₃⁻). (Nitrobacter reproduce by budding)
Both Nitrosomonas and Nitrobacter are nitrifying autotrophic bacteria, meaning they derive their energy from the oxidation of inorganic compounds and use carbon dioxide as their carbon source for growth.
Denitrification
Denitrification is the final step in the nitrogen removal process. Denitrification is an anoxic process that converts nitrate (NO₃⁻) to nitrogen gas (N₂), which is then released into the atmosphere.
In the anoxic process (No dissolved oxygen, but still bound Oxygen in (NO₃⁻)), Nitrate-reducing bacteria (NRB) break the nitrate molecule (NO₃⁻) and use the oxygen as their oxygen source, releasing nitrogen gas (N2) into the atmosphere through nitrogen gas bubbles.
Denitrifying Bacteria:
Nitrate-reducing bacteria (NRB) are heterotrophic bacteria, meaning they rely on organic compounds (Normal Wastewater BOD) for their carbon source. Common denitrifying bacteria include Pseudomonas, Paracoccus, and Bacillus.
Carbon (Food) Source for Denitrification:
In the denitrification process, while heterotrophic denitrifying bacteria, using the bound oxygen from nitrate (NO₃⁻) as their oxygen source, still require carbon (CBOD) as their main food source.