Denitrification

Molecular nitrogen (N2) can be produced by the reduction of nitrate (NO3) in a microbially aided process that involves the production of a succession of intermediate gaseous nitrogen oxide products before the production of molecular nitrogen (N2). Denitrification is a type of respiration performed by facultative anaerobic bacteria in response to the oxidation of an electron donor such as organic matter.

 It is a type of respiration in which oxidised forms of nitrogen are reduced. The most preferred nitrogen electron acceptors, in order of most to least thermodynamically favourable, are nitrate (NO3), nitrite (NO2), nitric oxide (NO), nitrous oxide (N2O), and finally dinitrogen (N2), which completes the nitrogen cycle. Nitric oxide (NO), nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2) are the least preferred nitrogen electron acceptors Denitrifying microorganisms require an extremely low oxygen concentration of less than 10 percent, as well as organic C for energy production, in order to thrive. Because denitrification may remove NO3 from sewage, thus limiting its leaching into groundwater, it can be used strategically to treat sewage or animal leftovers that have a high concentration of nitrogen. Denitrification has the potential to release N2O, which is an ozone-depleting material as well as a greenhouse gas that has the potential to have a significant impact on global warming.

What is the process of denitrification?

During the process of denitrification, the nitrogen component is released back into the environment, and this is accomplished by turning the nitrate (NO3-) into gaseous nitrogen (N).

Clostridium and Pseudomonas bacteria, which are prevalent in the soil, are responsible for the process of denitrification, which occurs when there is a deficiency of oxygen in the environment. The genus of Gram-negative bacteria involved in this process destroys nitrate compounds found in soil and aquatic systems, resulting in the production of nitrous oxide (N2O) and nitrogen gas, which are then released into the atmosphere.

This process involves a huge number of different microorganisms, which is why it is referred to as the microbial process as well.

This biogeochemical process is one of the most important responses to variations in the amount of oxygen (O2) present in the environment. A universal process for both terrestrial and aquatic ecosystems, denitrification occurs naturally under extreme concentrations in managed ecosystems – marine and freshwater environments, tropical and temperate soils, wastewater treatment plants, aquifers, manure stores, and so on. Denitrification can occur in both natural and managed ecosystems.

How does denitrification occur?

The process of denitrification is the final phase in the nitrogen cycling process. A naturally occurring, microbially mediated process in which nitrate is used as an energy source for denitrifiers, nitrate reduction is described here.

Soil bacteria convert plant-available soil nitrate (NO3–) into nitrogen (N) gases, which are then removed from the soil during the decomposition process. Denitrification results in the production of numerous gases, including nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2).

The process of denitrification is depicted in the flowchart below:

Nitrite  →  Nitric Oxide  →   Nitrous oxide  →  Nitrogen gas.

Where does denitrification occur?

Denitrification occurs in a variety of environments.

N2O (nitrous oxide) and the tropospheric pollutant nitric oxide are released as a result of denitrification, which is a microbial process that removes precious nitrogen from soil and releases the greenhouse gas nitrous oxide (N2O) (NO). The biological cycle of denitrification is characterised by a series of enzymes that convert nitrate to dinitrogen in a sequential manner.

What causes denitrification to take place?

When the oxygen (O2) supply in the soil becomes depleted, a variety of bacteria begin to use oxygen for respiration rather than nitrate as a source of energy. Denitrification happens most frequently in damp, moist, or flooded soils, where the supply of oxygen for respiration has been decreased or is completely depleted. Even while some fungi are capable of denitrification, their presence is not regarded as important.

When does the process of denitrification take place?

Denitrification is more active in areas where the proportion of water-filled pore space in the soil exceeds 60 percent of the total. The end-product gas is influenced by the soil conditions as well as the microbial community in the soil. As the oxygen scarcity develops, bacteria execute their activities by converting more of the nitrate into dinitrogen (N2) gas, which is released into the atmosphere. Denitrification occurs in the loss of vital nitrogen (N) for the purposes of nutrient management, however the impact on the environment will vary.

Factors that have an impact on the denitrification process

A number of elements have an impact on the entire denitrification process, including the following:

It is the presence of organic matter in the soil that has the most influence on the process of denitrification. The bacteria’s only source of sustenance comes from the organic stuff found in the soil itself. As a result, soil bacteria require a source of readily available organic matter, which can be obtained from plants, the soil, or from other sources in addition to those mentioned above.

Other considerations are as follows:

• pH of the soil.
• Texture of the soil.
• Temperature.
• The amount of oxygen in the soil.
• The amount of moisture in the soil.
• The amount of nitrate present in the soil.

Conclusion

Gaseous N loss can be caused by three different soil-based mechanisms. The generation of in soils and sediments is extremely tightly tied to denitrification and nitrifier denitrification, which are biological mechanisms. The chemodenitrification pathway is likewise linked to biological processes, however it happens in an acidic environment due to instability. A decreased C source, a pool, and an O2-limited environment are all required for denitrification activity. Because of the interactions between the three components, different proportions of N2O and N2 can be created. Increased concentration can enhance the N2O to N2 ratio produced by the denitrification pathway. Reduced O2 concentration, pH levels, and higher C availability can all help to boost the ratio. The importance of nitrifier denitrification processes, as well as the geographical variation of soil C and N and low O2 pressures required for denitrification during field quantification, are critical areas of research that must be understood before gaseous N loss can be managed.