Nitrification inhibition

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 ... 

Furthermore, the detection of nitrification inhibitor compounds is possible in wastewater. The principle of detection of nitrification inhibition is shown in Fig. 3. When starting such investigations, the sensor is first exposed to a surplus of substrate (ammonium or urea). The basic current becomes stable at a low... 

Fig. 3. Principle of detection of nitrification inhibiting effects with the nitrification biosensor...

Performing investigations with several pure substances which are known to act as nitrification inhibitors as well as investigations with polluted environmental samples demonstrated the suitability of the biosensor to detect nitrification inhibition (see Table 8). 

Table 8. Determination of nitrification inhibition of pure substances and wastewater samples with nitrifiers containing biosensor [80,82,83]...

Okey, R.W., Stensel, H.D. and Martis, M.C. (1996b). Modeling Nitrification Inhibition. Water Sci.TechnoL, 33,101-107. 

The nitrification inhibition test AQC data for different batches of the test organism, Nitrosomonas, has given a range of EC50 values of 0.76 to 1.28 mg l-1. The plot of EC50 values for 3,5 dichlorophenol is given in Figure 3.1.4. 

Microorganisms seem to be more sensitive to soil lead pollution than plants. Delayed composition may occur at 750 mg Pbkg soil, and nitrification inhibition at 1 gkg (US EPA 1986). Lead may interfere with several processes in the development of the plant, including growth, maintenance, and photosynthesis (Koeppe 1981). 

The method using the production of total oxidized nitrogen to measure inhibition is easy to carry out, makes it possible to screen a large number of samples without any specific equipment, and directly measures nitrification inhibition. 

If a substance is not readily biodegradable, this does not necessarily imply that the substance is toxic to microorganisms. Therefore, specific experiments on bacteria are carried out to obtain information on substance ecotoxicity. Examples are the respiratory inhibition test (e.g., OECD 209, [45]) and the nitrification inhibition test (ISO 9509, [46]), which are performed on a mixed microbial population representative of a sewage treatment plant s community, cell multiplication inhibition test on Pseudomonas putida (ISO 10712, [47]) and flash tests on luminescent bacteria Photobacterium phosphoreum [22] and Vibrio fischeri [24], which reduce their luminescence when exposed to toxic substances. 

Miller LG, MD Coutlakis, RS Oremland, BB Ward (1993) Selective inhibition of ammoninm oxidation and nitrification-linked NjO formation by methyl finoride and dimethyl ether. Appl Environ Microbiol 59 2457-2464. 

Osislo, A. and Lewandowski, Z., Inhibition of nitrification in the packed bed reactors by selected organic compounds, Water Res., 19, 423-426, 1985. 

The nitrification reactions are inhibited by high concentrations of ammonia. 

Lodhi, M.A.K. and Killingbeck, K.T. (1980). Allelopathic inhibition of nitrification and nitrifying bacteria in a ponderosa pine (Pinus ponderosa Dough) community. American Journal of Botany 67 1423-1429. 

There was no significant effect of aeration rate on the destmction of TS, VS, VFA or COD, thus the only saving in oxygen consumption of using redox control rather than DO control was in the inhibition of nitrification. 

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). 

Uses Rubber accelerator solvent in fiber and plastic industry rocket fuels lubricants condensers to increase dielectric constant industrial solvent antioxidant nematocide softener of copolymers research chemical plasticizer in acrylonitrile polymers inhibit nitrification in soil chemical intermediate for 1,1-dimethylhydrazine. 

Nitrification in soils is inhibited when bromacil is applied at a concentration of <50 ppm (Debona and Audus, 1970). The half-life in soil is approximately 10 d (Hartley and Kidd, 1987). 

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