NITRIFICATION AND DENITRIFICATION

NITRIFICATION AND DENITRIFICATION

NITRIFICATION

Nitrification is a biological process of oxidation of ammonia into nitrite and then to nitrate by nitrifying bacteria. It is an aerobic process and performed by chemoautotrophic bacteria.

Nitrification is a part of the nitrogen cycle where living beings oxidize ammonia present in the soil into useful forms of nitrogen which can be utilized by various organisms.

The reactions involved in nitrification are the following:

2NH₃⁺ + 3O₂        →    2NO₂^– + 2H⁺ + 2H₂O (Nitrosomonas and Nitrosococcus)

2NO₂^–   + O₂          →            2NO₃^–       (Nitrobacter and Nitrospira)

• The process consists of two reaction steps, and two different groups of microorganisms are involved in this process. Here the first step of oxidation of ammonia is carried out by bacteria of the genus Nitrosomonas and Nitrosococcus.
• The second reaction is performed by bacteria of the genus Nitrobacter and  All of these microorganisms are chemoautotrophs that utilize the energy from the reaction to produce organic carbon compounds.
• Thus, Nitrification process is important in agricultural systems where ammonia is used as a fertilizer. Because ammonia is converted into nitrate, this is absorbed and utilized by plants.
• Nitrifying bacteria also play an important role in wastewater treatment where different nitrogen compounds are converted into nitrates and then nitrogen before removing the gas out of the water.
• The nitrification process is controlled by a number of factors like the availability of oxygen, soil moisture, and the availability of ammonia.
• The activity of the nitrifying bacteria also decreases in acidic conditions and at a temperature above 35°C.

DENITRIFICATION

Denitrification is a biological process of reduction of nitrate into nitrite, which is then followed by the reduction of nitrate into nitrogen gas that results in the release of nitrogen gas into the air.

• It is the microbial process like nitrification but opposite of nitrification. Here nitrate present in the soil is reduced by denitrifying bacteria such as, Pseudomonas and Thiobacillus to nitrogen.
• It is also an important step in the nitrogen cycle where nitrogen is released back in gaseous forms, mainly nitrous oxide (NO₂) and nitrogen gas (N₂) into the atmosphere from the ground.
• Denitrification, unlike nitrification, is performed by facultative anaerobes that perform denitrification as anaerobic respiration to reduce oxidized forms into gases.
• The process of denitrification takes place through a set of half-reactions, which are:

NO₃^– + 2H⁺ + 2e^–    →   NO₂^– + H₂O

NO₂⁻ + 2 H⁺ + e⁻   →   NO + H₂O

2NO + 2 H⁺ + 2 e⁻ →   N₂O + H₂O

N₂O + 2 H⁺ + 2 e⁻ →   N₂ + H₂O

The overall reaction can be illustrated as:

2 NO₃⁻ + 10 e⁻ + 12 H⁺    →    N₂ + 6 H₂O

• The process is mostly performed by heterotrophic bacteria like Paracoccus denitrificansand some species of Pseudomonas, but some autotrophic denitrifiers like Thiobacillus denitrificans are also present.
• Denitrification is an important microbiological process that is performed naturally in both terrestrial and marine environments.
• Besides, denitrification follows nitrification in wastewater treatments to convert nitrogen-rich compounds into nitrogen gas before being released into the atmosphere.
• Denitrification can be disadvantageous by removing the NO3– present in the soil, thus reducing the extent of leaching.
• Denitrification is controlled by various factors like the concentration of oxygen and carbons, even though some aerobic bacteria of the genus Proteobacteria, might facilitate denitrification even in the presence of oxygen.

Key Differences

Frequently Asked Question (FAQ)
Nitrification process is carried out by genus of bacteria namely:
Amonia to Nitrite by Nitrosomonasand Nitrosococcus and Nitrite to Nitrate by genus Nitrobacter.

Denitrification process is carried out by:
Denitrifying bacteria such as, Pseudomonas and Thiobacillus to nitrogen.