Nitrification and Denitrification

The general equations of coupled oxic respiration and nitrification (6.1) and denitrification 

In the following step nitrite is oxidized by lithotrophs like Nrobacter or Nrococcus to nitrate (Eq. 6.5)  

The reduction of nitrate to dinitrogen occurs first as a reduction of nitrate to nitrite (Eq. 6.6) and then a stepwise reduction to nitrogen oxide, dinitrogen oxide (Eq. 6.7) and dinitrogen (Eq. 6.8)  

Denitrification starts when oxygen is almost depleted (below the oxygen penetration depth) by inducing an enzymatic system of nitrate reductase and nitrite reductase by facultative aerobic bacteria, which can only use nitrogenous oxides if oxygen is - nearly - absent. Measurements carried 

The Role of Oxygen, Nitrate and Phosphorus in Marine Sediments 

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Denitrification is a process in which facultative organisms will reduce nitrate to nitrogen gas in the absence of molecular oxygen. This consequendy results in the removal of BOD. The denitrification process also generates one hydroxyl ion so that alkalinity requirements are reduced to half when both nitrification and denitrification are practiced. 

The interest in gaseous losses of nitrogen from soil is now extensive and includes the well established community of soil scientists concerned with losses of fertilizer-applied nitrogen by nitrification and denitrification. More recently, interest in ammonia losses from plants and soil has been stimulated by the very large emissions from intensive cattle production in the Netherlands and their... 

Figure 6 The production and emission of NO and N,0 during nitrification and denitrification. NO / ...

In soil, microbial nitrification and denitrification are the predominant sources of NO and NjO and the emission fiiixes may be regarded as leakage during the transformation processes shown in Figure 6. Nitrifiers can produce NO and NjO during the oxidation of NH4 to NO3". Both gases are by-products of the nitrification pathway and the typical yield of NO in well-aerated soil is 1-4% of the NH4 oxidized and for NjO is less than... 

Attached growth processes Wastewater treatment processes in which the microorganisms and bacteria treating the wastes are attached to the media in the reactor. The wastes being treated flow over the media. Trickling filters, bio-towers, and RBCs are attached growth reactors. These reactors can be used for removal of BOD, nitrification, and denitrification. 

Because the nitrification and denitrification processes both form N2O as a by-product, control of anthropogenic N inputs to the soil in the form of synthetic fertilizers or manure would affect the amount of N2O produced... 

Different kinds of bioreactors and configurations have been used to treat wastewater containing formaldehyde and urea, and three different kinds of treatments can be applied anaerobic treatment, aerobic treatment, and combined nitrification and denitrification treatments. 

To maintain high recycling ratios between the nitrification and denitrification units. This recommendation is also useful to increase the efficiency of nitrogen removal. 

The emission of N20 from manure occurs directly by both nitrification and denitrification of nitrogen contained in the manure. This emission mainly depends on the N and C content of the manure during various types storage and treatment. The nitrification process strictly needs oxygen, while subsequent denitrification is an anaerobic process. 

Texier AC, Zepeda A, Gomez J, Cuervo-Lopez F. Simultaneous elimination of carbon and nitrogen compounds of petrochemical effluents by nitrification and denitrification. Chapter 6. In Patel V (ed.), Petrochemicals. Rijeka, Croatia Intech 2012, pp. 101-134. Available at http //www.intechopen.com. Accessed June 3,2013. 

Microbiological conversion in molecular nitrogen by means of nitrification and denitrification, often in combination with the removal of organic pollutants... 

In the step-feed system used for nitrification and denitrification the feed is introduced along the length of the basins into anoxic ones formed at these entry points (Figure 4). This system has the advantage that a large portion of the mixed liquor is retained in the first number of sections, which allows the breakdown of adsorbed carbonaceous matter and ensures that the nitrifiers are not washed out of the system. However, since a portion of the influent organic carbon and ammonia enters near the end of the tank, some will wash... 

Autotrophic activity. Because of the low C N ratio and its declining value as carbonaceous residues are degraded there is substantial ammonification. With all mean treatment times greater than the doubling time of Nitrobacter sp. nitrification will occur provided that oxygen is not limiting. Smith and Evans (19) found that with DO levels above 15% of saturation, nitrification continued until the culture was limited by a fall in pH level. Up to 40% of the slurry ammonia was oxidised. The autotrophic activity never achieved steady state and cycled between periods of activity when the pH value was above about 5.5 and periods of inactivity when the pH value fell below 5.5. Complete nitrification of all ammonia only occurred if the pH value was controlled at about 7 by the addition of alkali. When the DO level was held within the range of 1 to 15% of saturation a system of simultaneous nitrification and denitrification was established. The reduction of nitrate allowed the pH value to remain above 6 and nitrification to continue. Thus more than 70% of the ammonia was oxidised. If the DO level was held below 0.1% of saturation, nitrification was inhibited (unpublished). 

ASMl- A basic model dealing with nitrification and denitrification in wastewater,... 

Emissions of nitric and nitrous oxides are the result of microbial nitrification and denitrification in soils, controlled principally by soil water and mineral N contents, labile organic carbon, and temperature. Nitric oxide is a direct intermediate of both nitrification... 

It is thought that little net NO is produced in denitrification, it being readily reduced to N2O, and nitrification is therefore the main source of NO (Anderson and Levine, 1986 Skiba et al, 1993). Nitrous oxide is also produced in both nitrification and denitrification. At low O2 concentrations in otherwise aerobic soil, small amounts of N2O are formed as a by-product of nitrification, N2O not itself being reduced to NO,. In denitrification, the proportion of N2O produced relative to N2 increases as the availability of O2 increases and that of carbon decreases (Tiedje, 1988). In general only a small fraction of the N nitrified or denitrified in these pathways is released as NO or N2O. The emission is therefore sensitive to the amount of mineral N in the system, which is driven principally by additions of nitrogen fertilizers and deposition of nitrogen from the atmosphere. 

Skiba U, Smith KA, Fowler D. 1993. Nitrification and denitrification as sources of nitric oxide and nitrous oxide in a sandy loam soil. Soil Biology and Biochemistry 25 1527-1536. 

Nitrous oxide is important not only as a greenhouse gas but, as discussed in Chapter 12, as the major natural source of NC/ in the stratosphere, where it is transported due to its long tropospheric lifetime (Crutzen, 1970). The major sources of N20 are nitrification and denitrification in soils and aquatic systems, with smaller amounts directly from anthropogenic processes such as sewage treatment and fossil fuel combustion (e.g., see Delwiche, 1981 Khalil and Rasmussen, 1992 Williams et al., 1992 Nevison et al., 1995, 1996 Prasad, 1994, 1997 Bouwman and Taylor, 1996 and Prasad et al., 1997). The use of fertilizers increases N20 emissions. For pastures at least, soil water content at the time of fertilization appears to be an important factor in determining emissions of N20 (and NO) (Veldkamp et al., 1998). 

Kuenen, J. G., and Robertson, L. A. (1987). Ecology of nitrification and denitrification. In The Nitrogen and Sulfur Cycles (J. A. Cole and S. Ferguson, eds.), Symp. No. 42, pp. 161-218. Society of General Microbiology, Cambridge Univ. Press, London. 

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