Question

What is nitrification?

Answer 1

Hint: Nitrification plays a very important role in the removal of nitrogen from municipal wastewater. The conventional process of removal is nitrification, which is followed by denitrification. The cost of this entire process resides mainly in the aeration and addition of an external carbon source e.g., methanol for denitrification.

Complete answer:
Nitrification is the process of biological oxidation of ammonia into nitrite which is followed by oxidation of the nitrite into nitrate. The transformation of ammonia into nitrite is the rate-limiting step of nitrification. Nitrification is a significant step in the nitrogen cycle in soil. It is an aerobic process that is performed by small groups of various autotrophic and archaea bacteria. The process of nitrification was discovered by the Russian microbiologist Sergei Winogradsky.
The oxidation of ammonia in nitrite is usually performed by two groups of organisms, namely, ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). AOBs are found among β-proteobacteria and gammaproteobacteria. Two AOA, namely, Nitrosopumilus maritimus and Nitrososphaera viennensis, are being isolated and described.
The second step involved during nitrification is the oxidation of nitrite into nitrate. It is carried out by a bacterium of the genus Nitrobacter and Nitrospira. These two steps produce energy that is later coupled for ATP synthesis. Nitrifying organisms follow chemoautotrophic for deriving nutrition, and carbon dioxide is used as the carbon source for growth.
Additional Information:
Some soil conditions that control nitrification rates:
-Substrate availability (presence of ammonium salts)
-Aeration (availability of oxygen)
-Well-drained soils with adequate soil moisture content
-pH (near neutral)
-Temperature

Note: Nitrification inhibitors are the chemical compounds that slow the nitrification rate of ammonia, ammonium, or urea-containing fertilizers that are applied to the soil as fertilizers. These inhibitors help in reducing losses of nitrogen in the soil, which would otherwise be used by crops. Nitrification inhibitors are being used widely and are added to approximately half of the fall-applied anhydrous ammonia in states in the U.S. These are effective in increasing the recovery of nitrogen fertilizer in row crops. The level of effectiveness depends upon external conditions, and the benefits are likely to be seen at less than optimal nitrogen rates.