Main Difference – Nitrification vs Denitrification
Nitrogen is an essential element for life on earth. It acts as a component in protein, nucleic acids, and many other important compounds. Nitrogen circulates throughout the environment via the nitrogen cycle. The major steps of nitrogen cycle include nitrogen fixation, nitrogen assimilation, ammonification, nitrification, and denitrification. Hence, nitrification and denitrification are two important stages of the nitrogen cycle. Nitrification is the biological conversion of ammonium into nitrate. Denitrification is the biological conversion of nitrate into nitrogen gas. This is the main difference between nitrification and denitrification. Both these conversions are biological since these conversions are done by microbes.
Key Areas Covered
1. What is Nitrification
– Definition, Process
2. What is Denitrification
– Definition, Process, Application
3. What is the Difference Between Nitrification and Denitrification
– Comparison of Key Differences
Key Terms: Ammonium, Ammonia Oxidizing Microorganisms, Denitrification, Nitrate, Nitrification, Nitrifying Bacteria, Nitrogen, Nitrogen Cycle, Nitrite Oxidizing Microorganism
What is Nitrification
Nitrification is a stage of the nitrogen cycle in which ammonium is converted into nitrate either by biological or chemical means. Nitrification is an oxidation process. Here, reduced forms of inorganic and organic nitrogen, mainly ammonium, are converted into nitrate, which is an oxidized form of nitrogen.
Nitrification is a biological process which is mediated by microorganisms. This stage of nitrogen cycle includes two chemical reactions. As the first step, ammonium is converted into nitrite, followed by the oxidation of nitrite into nitrate. This process is beneficial for microorganisms since they can derive energy required for their growth through these chemical reactions. These microorganisms are known as nitrifying microorganisms.
Since the nitrification process includes two chemical reactions, there are two groups of nitrifying microorganisms involved in nitrification. One group is ammonia oxidizers and the other group is nitrite oxidizing microorganisms.
Figure 1: Nitrogen Cycle
Ammonia Oxidizing Microorganisms
This group of microorganisms includes obligate autotrophs and ammonia-oxidizing archaea. The most common and well-known bacteria in this process is Nitrosomonas. They can mediate the conversion of ammonia or ammonium into nitrite as follows.
NH4+ + 1.5O2 → NO2– + H2O + H+
Nitrite Oxidizing Microorganism
This group includes bacteria that can convert nitrite into nitrate. The most common and well-known bacteria in this process is Nitrobactor. The reaction is as follows.
NO2– + 0.5O2 → NO3–
Nitrification depends on few factors. Like most bacteria, nitrifying bacteria are temperature sensitive. The maximum nitrification rate can be observed at optimum temperature for nitrifying bacteria (0-35oC). and also, these bacteria are extremely sensitive to low oxygen concentrations. The rate of nitrification falls at low oxygen concentrations. The nitrification is fastest at pH values around 8-9. In addition, the presence of inhibiting substances can limit nitrification. All these factors affect the growth of nitrifying bacteria.
What is Denitrification
Denitrification is a stage of the nitrogen cycle in which oxidized forms of nitrogen are converted into nitrogen gas either by biological or chemical means. This is a reduction reaction. Nitrate is the oxidized form of nitrogen and denitrification converts this oxidized form into reduced form: nitrogen gas. Here, the oxidation state of nitrogen changes from +5 to 0.
Same as nitrification, denitrification is a biological process. This is because this conversion of nitrate is mediated by microorganisms. The major class of bacteria that is involved in denitrification are facultative anaerobes. The oxidized forms of nitrogen that undergo denitrification are nitrates and nitrites.
Figure 2: Denitrification by Biological Means
Denitrification Reaction
NO3– → N2O → N2
One major application of denitrification is in water purification. Denitrification can remove nitrogen species from water in the form nitrogen gas. Denitrification can be done in three methods for water treatment: ion exchange, chemical reduction, and biological denitrification. In ion exchange process, unwanted ions such as nitrates are exchanged with other ions followed by the removal of nitrate ions. In chemical reduction, reducing agents are used to reduce nitrate into nitrogen gas. The biological denitrification uses denitrifying microorganisms such as Thiobacillus and Pseudomonas.
Difference Between Nitrification and Denitrification
Definition
Nitrification: Nitrification is a stage of the nitrogen cycle where ammonium is converted into nitrate either by biological or chemical means.
Denitrification: Denitrification is a stage of the nitrogen cycle where oxidized forms of nitrogen are converted into nitrogen gas either by biological or chemical means.
Process
Nitrification: Nitrification includes the conversion of reduced nitrogen species into oxidized nitrogen species.
Denitrification: Denitrification includes the conversion of oxidized nitrogen species into reduced nitrogen species.
End Product
Nitrification: The end product of nitrification is nitrate.
Denitrification: The end product of denitrification is nitrogen gas.
Starting Species
Nitrification: Nitrification starts with ammonia or ammonium ions.
Denitrification: Denitrification starts with nitrate.
Microorganisms
Nitrification: Nitrification is mediated by nitrifying microorganisms such as Nitrosomonas, Nitrobacter.
Denitrification: Denitrification is mediated by denitrifying microorganisms such as Thiobacillus and Pseudomonas.
Conclusion
Nitrification and denitrification are two main steps of the nitrogen cycle. Nitrogen cycle is the circulation of nitrogen in the environment. The main difference between nitrification and denitrification is that nitrification is the conversion of ammonium into nitrate whereas denitrification is the conversion of nitrate into nitrogen gas.
References:
1. “Denitrifying bacteria.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 14 Dec. 2011, Available here.
2. “Nitrification.” Encyclopedia of Life Sciences, Available here.
Image Courtesy:
1. “Nitrogen Cycle” By Cicle_del_nitrogen_de.svg: *Cicle_del_nitrogen_ca.svg: Johann Dréo (User:Nojhan), traduction de Joanjoc d’après Image:Cycle azote fr.svg.derivative work: Burkhard (talk)Nitrogen_Cycle.jpg: Environmental Protection Agencyderivative work: Raeky (talk) – Cicle_del_nitrogen_de.svgNitrogen_Cycle.jpg (CC BY-SA 3.0) via Commons Wikimedia
2. “1.12 Buffers for nitrogen” by National Agroforestry Center (CC BY 2.0) via Flickr
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