Denitrification


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.

denitrification

[dē‚nī·trə·fə′kā·shən]
(chemistry)
(microbiology)
The reduction of nitrate or nitrite to gaseous products such as nitrogen, nitrous oxide, and nitric oxide; brought about by denitrifying bacteria.

Denitrification

 

a process occurring widely in nature whereby nitrates are reduced to molecular nitrogen by bacteria. Denitrification takes place with the formation of nitrites and nitrogen oxide according to the scheme

2HNO3→2HNO2→N2O→N2

The bacteria obtain the energy necessary to reduce nitrates from the oxidation of organic matter (carbohydrates, alcohols, and organic acids), and the nitrate oxygen is an electron and hydrogen acceptor. The denitrification that takes place during the oxidation of glucose can be expressed by the equation

5C6H12O6 + 24KNO3→24KHCO3 + 6CO2 + 12N2 + 18H2O

There are also unusual species of denitrifying bacteria that reduce nitrates by oxidizing sulfur or molecular hydrogen. Denitrification is severely inhibited or ceases completely in the presence of molecular oxygen. It should not be confused with the reduction of nitrates to ammonia, a process associated with the assimilation by microorganisms of nitrates as a source of nitrogen. Many bacteria possess this ability as well as actinomycetes and fungi, which in general are incapable of inducing nitrification. Denitrification must be distinguished from pseudonitrification, in which a purely chemical reaction between nitrites and ammonium salts, amines, or amides takes place in a bacteria culture or in nature and which results in the release of molecular nitrogen. For example, NH4Cl + HNO2→N2 + HCl + 2H2O. One gram of soil contains tens and hundreds of thousands of dentrifying bacteria. However, denitrification can take place vigorously in soil only under certain conditions: when there is a sufficient quantity of nitrates and nitrogen-free organic matter readily decomposed by microorganisms, at optimum pH (7.0-8.2) and temperature (25°-30°C), and, most important, under anaerobic conditions. That is why denitrification is very intensive in moist, poorly aerated soils. During denitrification the amount of nitrogen in the soil decreases owing to the release of molecular nitrogen and traces of nitrous oxide. This results in a decrease in soil productivity. Seventy-five percent of nitrate nitrogen escapes from the soil in the form of molecular nitrogen ten days after nitrates and plant residues have been added to clayey soil. Good aeration of the soil (by cultivation), a decrease in the moisture content of the soil at certain times (through drainage), and the creation of conditions for the better use of soil nitrates by cultivated plants are measures that help reduce denitrification.

A. A. IMSHENETSKII

References in periodicals archive ?
In the paper titled, "Comparison of denitrification performance by bacterium Achromobacter sp.
In general, [N.sub.2]O emissions from soil are regulated at two levels, which are the rates of nitrification and denitrification in the soil and soil physical factors regulating the ratio of [N.sub.2]O to other nitrous gases (Davidson et al.
Because the A/O process has both nitrification and denitrification applications, it can remove not only ammoniacal nitrogen but also TN by using a reflux nitrification liquid.
In the present study, the results indicated that different fertilization managements were significantly affected some physiological function soil microbial quantity, including the soil nitrifying and denitrification, ammonifiers, cellulose-decomposing and azotobacteria bacteria.
Aerobic denitrification medium (ADM) contained (per liter) 7.0 g [K.sub.2]HP[O.sub.4], 3.0 g [KH.sub.2]P[O.sub.4], 0.1 g MgS[O.sub.4] x 7[H.sub.2]O,1.45 g KNO3 (ADM-1) or 0.986 g NaN[O.sub.2] (ADM-2), 0.05 g FeS[O.sub.4] x 7[H.sub.2]O, and 10 g C[H.sub.3]COONa, pH 7.2.
denitrification to total [N.sub.2]O fluxes can vary widely, and the ability to develop robust mitigation strategies remains compromised.
Even when N[O.sub.3.sup.-]-N concentrations in [CSAS.sub.C]'s final effluent (Ef) were low, processes of N[O.sub.3.sup.-]-N removal like denitrification could have occurred only in low rates because the environmental conditions in CR and SR were predominantly aerobic, however, a possible presence of anoxic microzones and a complete anoxic environment in the bottom of the SS could have promoted incipient denitrification.
Since the air-diffuser position resulted in the formation of aerobic or anoxic zone, the performance of nitrogen removal through SND might be compared to the separated reactions of nitrification and denitrification. Thus, two biofilm reactors had the air-diffuser at one-third of the reactor and the other two reactors had the air-diffuser at the bottom of the reactor for three months.
Advantages of Phospho-gypsum coating is when Phospho-gypsum slurry applied on urea forms fine coating and protects the loss of nitrogen by denitrification ensuring regulated continuous availability of nitrogen for a longer period as per the requirement of crops.