Nitrification Nitrobacter

Aerobic The reactions carried out by Nitrosomonas and Nitrobacter (reactions b and c, autotrophic respectively) are known as nitrification, while those carried out by Beggiatoa and Thiobacillus thiooxidans (reactions d and e, respectively) are examples of sulfur oxidation ... 

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 If the DO level was held below 0.1% of saturation, nitrification was inhibited (unpublished). 

In the proeess of generating biological growth you will need to watch the alkalinity of the soils, even when localized. In achieving nitrification, ammonia is consumed, but so is about 1.83 moles of Alkalinity as HC03-for every mole of Ammonia consumed by nitrosomanas and nitrobacter. 

Konig et al. [80-84] demonstrated that microbial sensors are suitable for the summary quantification of nitrifiable compounds (see also Sect. 3.3.1) as well as for the detection of nitrification inhibiting effects. Such biosensors, which contain a mixed population of the nitrifying bacteria Nitrosomonas sp. and Nitrobacter sp., exhibit a specific supplementary metabolic capacity. This enables the amperometric determination of ammonia according the following scheme of nitrification ... 

The oxidation of ammonia to nitrite, in the process of nitrification, is brought about mainly by autotrophic bacteria such as Nitrosomonas species. The oxidation of nitrite to nitrate is due to the action of Nitrobacter species. 

Nitrification. In biological nitrification ammonium nitrogen is oxidized into nitrite by means of Nitrosomonas species, and nitrite is oxidized to nitrate by the Nitrobacter species. 

In some cases, the effects of complex environmental mixtures could be accounted for in terms of concentration-additive effects of a few chemicals. In sediments of the German river Spittelwasser, which were contaminated by chemical industries in its vicinity, around 10 chemicals of a cocktail of several hundred compounds were found to explain the toxicity of the complex mixture to different aquatic organisms (Brack et al. 1999). The complex mixture of chemicals contained in motorway runoff proved toxic to a crustacean species (Gammarus pulex). Boxall and Maltby (1997) identified 3 polycyclic aromatic hydrocarbons (PAHs) as the cause of this toxicity. Subsequent laboratory experiments with reconstituted mixtures revealed that the toxicity of motorway runoff could indeed be traced to the combined concentration-additive effects of the 3 PAHs. Svenson et al. (2000) identified 4 fatty acids and 2 monoterpenes to be responsible for the inhibitory effects on the nitrification activity of the bacteria Nitrobacter in wastewater from a plant for drying wood-derived fuel. The toxicity of the synthetic mixture composed of 6 dominant toxicants agreed well with the toxicity of the original sample. 

Based on Reactions 8.14 and 8.15, nitrification is energetically favorable (overall AG° = -84 kcal). The intermediate nitrogen form, NO , rarely accumulates in significant concentrations because nictrobacter normally acts as fast or faster than the N02-producing bacteria. However, nitrobacter is more sensitive to ammonia than nitrosomonas, and for this reason nitrite may accumulate under high concentrations of NH (Fig. 8.5) but not under low concentrations of NH4 (Fig. 8.6)... 

Various soil processes also contribute to soil acidity. Decaying organic matter releases a number of organic acids, as indeed do plant roots. Nitrification, the microbial oxidation of ammonium ions to nitrate by Nitrosomonas and Nitrobacter, occurs in slightly acidic to neutral soils and releases H" " ions ... 

Nitrification seems limited to a number of autotrophic bacteria. The dominant genus that is capable of oxidizing ammonia to nitrite in soils is Nitmsomonas, and the dominant genus capable of oxidizing nitrite to nitrate is Nitrobacter. Normally, the two processes are closely connected and nitrite accumulation does not occur. Nitrifying bacteria are chemolithotrophs that utilize the energy derived from nitrification to assimilate C02. 

The reactions in the nitrification process are mediated by two types of autotrophic bacteria Nitrosomonas and Nitrobacter. The ammonia comes from the nitrogen content of any organic substance, such as proteins, that contains about 16% nitrogen. As soon as the ammonia has been hydrolyzed from the organic substance, Nitrosomonas consumes it and in the process also consumes oxygen according to... 

The Nitrosomonas and the Nitrobacter reactions may now be added to produce the overall nitrification reaction as shown next. 

The genera of bacteria that are responsible for nitrification are highly sensitive to acidity, so this process does not occur at significant rates in acidic soil or water, especially in those with pH less than 5.5. Plants that grow in acidic habitats such as bogs and some forests must be capable of utilizing ammonium as their source of nitrogen nutrition because nitrate is not available in those habitats. Because Nitrobacter is somewhat more sensitive to acidity and some other stresses than Nitro-somonas, nitrite can accumulate under some conditions. 

Nitrification—The process by which Nitro-somonas bacteria oxidize ammonium to nitrite which is then oxidized by Nitrobacter to nitrate. 

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