Denitrification transformations

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... 

Denitrification in activated sludge systems is well known and well described. However, only a few investigations of anoxic transformations relevant for sewer systems have been performed. 

Nitrogen uptake that results in the formation of new biomolecules is termed an assimilation process, such as assimilatory nitrogen reduction. The processes that result in the release of DIN into seawater are referred to as dissimilations, such as dissimi-latory nitrogen reduction. An example of the latter is denitrification, in which nitrate and nitrite obtained from seawater serve as electron acceptors to enable the oxidation of organic matter. This causes the nitrate and nitrite to be transformed into reduced species, such as N2O and N2, which are released back into seawater. 

Anaerobic metabolism occnrs nnder conditions in which the diffusion rate is insufficient to meet the microbial demand, and alternative electron acceptors are needed. The type of anaerobic microbial reaction controls the redox potential (Eh), the denitrification process, reduction of Mu and SO , and the transformation of selenium and arsenate. Keeney (1983) emphasized that denitrification is the most significant anaerobic reaction occurring in the subsurface. Denitrification may be defined as the process in which N-oxides serve as terminal electron acceptors for respiratory electron transport (Firestone 1982), because nitrification and NOj" reduction to produce gaseous N-oxides. hi this case, a reduced electron-donating substrate enhances the formation of more N-oxides through numerous elechocarriers. Anaerobic conditions also lead to the transformation of organic toxic compounds (e.g., DDT) in many cases, these transformations are more rapid than under aerobic conditions. 

Fine P, Yaron B (1993) Outdoor experiments on enhanced volatilization by venting on kerosene components from sods. J Contam Hydrol 12 355-374 Fioressi S, Arce R (2005) Photochemical transformation of benzo(e)pyrene in solution and adsorbed on silica gel and alumina surfaces. Environ Sci Technol 39 3646-3655 Firestone MK (1982) Biological denitrification. In Stevenson FJ (ed) Nitrogen in agricultural sods. Agronomy 22 289-326... 

Criddle CS, DeWitt JT, Grbic-Galic D, et al. 1990. Transformation of carbon tetrachloride by pseudomonas sp. strain KC under denitrification conditions. AppI Environ Microbiol 56 3240- 3246. 

Bouwer, E. J., and P. L. McCarty, Transformations of halogenated organic compounds under denitrification conditions , Appl. Environ. Mibrobiol., 45,1295-1299 (1983b). 

Nitrogen transformations such as nitrate assimilation, denitrification, and decomposition (eqs 10-12) contribute to alkalinity by consuming H+. In contrast, both ammonium assimilation and nitrification (eqs 13 and 14) consume alkalinity via the production of H +. 

Nitrate and Ammonium. The transformations of nitrogen species may occur under suitable microbial catalysis (5, 36). Nitrate reduction may result in formation of either elemental nitrogen or ammonium. Mass balances over a whole lake have indicated the importance of the denitrification process for the elimination of nitrogen from lakes (37). The conditions for the dis-similative ammonification of nitrate are poorly known (36). Ammonium is also released by the mineralization of biomass. 

In the anoxic zone of the Sea ammonia increases in a similar way as hydrogen sulfide (Fig. 4) and reaches maximum concentrations of about 90-100 pM in the bottom mixed layer. The losses of combined nitrogen due denitrification and the absence of nitrification in deep waters has transformed the Black Sea into an ammonium basin, where about 98% of total inorganic nitrogen stock is composed of NH4, while in the ocean 98-99% of it belongs to NO3 [23]. 

Cytotoxic effector substances produced by certain immune cells (such as -NO) that result in killing of their targets, typically abnormal cells or invading pathogen Denitrification the microbial transformation of nitrite and nitrate to N2... 

Ronner, U. (1985). Nitrogen transformations in the Baltic Proper Denitrification counteracts eutrophication. Ambio 14, 134—138. 

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