Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Nitrification”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23Linked to original sources
PubMed2005

Modelling nitrification, heterotrophic growth and predation in activated sludge.

A mathematical model describing the interaction between nitrifiers, heterotrophs and predators in wastewater treatment has been developed. The inclusion of a predation mechanism is a new addition to the existing activated sludge models. The developed model considered multi-substrate consumption and multi-species growth, maintenance and decay in a culture where nitrifiers, heterotrophs and predators (protozoa and metazoa) are coexisting. Two laboratory-scale sequenced batch reactors (SBRs) operated at different sludge retention time (SRT) of 30 and 100 days for a period of 4 years were used to calibrate and validate the model. Moreover, to assess the predator activity, a simple procedure was developed, based on measuring the respiration rate with and without the presence of the predators. The model successfully described the performance of two SBRs systems. The fraction of active biomass (ammonia oxidisers, nitrite oxidisers and heterotrophs) predicted by the proposed model was only 33% and 14% at SRT of 30 and 100 days, respectively. The high fraction of inert biomass predicted by the model was in accordance with the microscopic investigations of biomass viability in both reactors. The presented model was used to investigate the effect of increasing sludge age and the role of predators on the biomass composition of the tested SBR system.

Animals↗
PubMed2002

Nitrification in saline wastewater with high ammonia concentration in an activated sludge unit.

A nitrifying activated sludge reactor fed with a high salinity medium was operated efficiently at ammonia loading rates between 1 and 4 g NH4+ -N l(-1) d(-1). The system became completely inefficient at inlet salt concentrations higher than 525 mM due to the mixed inhibition effect of salts and ammonia. The final product was mainly nitrate although dissolved oxygen limitations caused sporadic ammonia and nitrite accumulations. Specific nitrifying activity decreased due to the saline effect. A set of activity tests showed that in the continuous reactor non-adapted biomass is rather more sensitive than biomass to the saline effect. Physical properties of biomass in the reactor (sludge volumetric index and zone settling velocity) were not affected by the saline concentration, a biomass concentration of 20 gVSS l(-1) was achieved.

Ammonia↗
PubMed1979

Chemical control of nitrification under rice in the central rainlands of the Sudan.

2-amino-4-chloro-6-methyl pyrimidine "AM" was used as a selective inhibitor of nitrifying organisms to prevent denitrification losses. Zero, 6, and 12 kg/ha of the chemical, 43 and 86 kg/ha urea-N or their equivalents were used in vitro and in vivo experiments. In the in vitro experiment, clear and significant inhibition lasted for 6 weeks. In both the pot and field experiments inhibition lasted shorter and only insignificant increases in yield and yield components were attained. The value of this chemical for rice under the soil and climatic conditions of the Central Rainlands seems to be small, though it seems promising for lighter (leaching) soils.

Ammonia↗
PubMed2003

Nitrification, denitrification and biological phosphorus removal in piggery wastewater using a sequencing batch reactor.

Nutrients in piggery wastewater with high organic matter, nitrogen (N) and phosphorus (P) content were biologically removed in a sequencing batch reactor (SBR) with anaerobic, aerobic and anoxic stages. The SBR was operated with 3 cycles/day, temperature 30 degrees C, sludge retention time (SRT) 1 day and hydraulic retention time (HRT) 11 days. With a wastewater containing 1500 mg/l ammonium and 144 mg/l phosphate, a removal efficiency of 99.7% for nitrogen and 97.3% for phosphate was obtained. Experiments set up to evaluate the effect of temperature on the process showed that it should be run at temperatures higher than 16 degrees C to obtain good removals (> 95%). Batch tests (ammonia utilization rate, nitrogen utilization rate and oxygen utilization rate) proved to be good tools to evaluate heterotrophic and autotrophic biomass activity. The SBR proved to be a very flexible tool, and was particularly suitable for the treatment of piggery wastewater, characterized by high nutrient content and by frequent changes in composition and therefore affecting process conditions.

Animals↗
PubMed1997

Enhancement of ethene removal from waste gas by stimulating nitrification.

The treatment of poorly water soluble waste gas compounds, such as ethene, is associated with low substrate concentration levels in the liquid phase. This low concentration level might hamper the optimal development of a microbial population. In this respect, the possible benefit of introducing nitrifying activity in the heterotrophic removal of ethene at moderate concentrations (< 1000 ppm) from a waste gas was investigated. Nitrifying activity is known to be associated with (i) the production of soluble microbial products, which can act as (co-)substrates for heterotrophic micro-organisms and (ii) the co-oxidation of ethene. The used reactor configuration was a packed granular activated carbon biobed inoculated with the heterotrophic strain Mycobacterium E3. The nitrifying activity was introduced by regular submersion in a nitrifying medium prepared from (i) compost or (ii) activated sludge. In both cases a clear enhancement of the volumetric removal rate of ethene could be observed. When combined with a NH3 dosage on a daily basis, a gradual increase of the volumetric removal rate of ethene could be observed. For a volumetric loading rate of 3 kg ethene-COD.m-3.d-1, the volumetric removal rate could thus be increased with a factor 1.8, i.e. from 0.72 to a level of 1.26 kg ethene-COD.m-3.d-1.

Air Pollutants↗
PubMed2004

Nitrification and anammox with urea as the energy source.

Urea is present in many ecosystems and can be used as an energy source by chemolithotrophic aerobic ammonia oxidizing bacteria (AOB). Thus the utilization of urea in comparison to ammonia, by AOB as well as anaerobic ammonia oxidizing (Anammox) bacteria was investigated, using enrichments cultures, inoculated with activated sludge, and molecular ecological methods. In batch enrichment cultures grown with ammonia a population established in 2 weeks, which was dominated by halophilic and halotolerant AOB as determined by fluorescence in situ hybridization (FISH) experiments, with the 16S rRNA targeting oligonucleotide probe NEU. In other batch enrichment cultures using urea, the AOB population was assessed by PCR amplification, cloning and phylogenetic analysis of amoA and ribosomal 16S rRNA genes. While only one of the 48 16S rRNA gene clones could be identified as AOB (Nitrosomonas oligotropha), the amoA approach revealed two more AOB, Nitrosomonas europaea and Nitrosomonas nitrosa to be present in the enrichment. FISH analysis of the enrichment with probe NEU and newly designed probes for a specific detection of N. oligotropha and N. nitrosa related organisms, respectively, showed that N. oligotropha-like AOB formed about 50% of the total bacterial population. Also N. nitrosa (about 15% of the total population) and N. europaea (about 5% of the total population) were relatively abundant. Additionally, continuous enrichments were performed under oxygen limitation. When ammonia was the energy source, the community in this reactor consisted of Anammox bacteria and AOB hybridizing with probe NEU. As the substrate was changed to urea, AOB related to N. oligotropha became the dominant AOB in this oxygen limited consortium. This resulted in a direct conversion of urea to dinitrogen gas, without the addition of organic carbon.

Aerobiosis↗
PubMed1995

Nitrification in vitro by a range of filamentous fungi and yeasts.

A wide range of fungi including yeasts, growing on Czapek Dox medium, nitrified added ammonium and the ammonium released by urea hydrolysis. Phanerochaete chrysosporium and Hymenoscyphus ericiae were the only fungi tested which failed to nitrify. A soil yeast (isolate 1) was the most active nitrifier of ammonium in vitro, forming 0.80 microgram nitrate mg-1 biomass over the 7 d incubation period.

Biomass↗
PubMed1977

Nitrification in histosols: a potential role for the heterotrophic nitrifier.

Insufficient populations of Nitrosomonas and Nitrobacter were found in a Pahokee muck soil (Lithic medidaprit) to account for the nitrate concentration observed. To determine if heterotrophic nitrifiers could account for some of this discrepancy, a method was developed to measure the levels of heterotrophic nitrifiers in soil. A population of 4.1 X 10(5) Arthrobacter per g of dry fallow soil, capable of producing nitrite and/or nitrate from reduced nitrogenous compounds, was observed. Amendment of the much with 0.5% (wt/wt) sodium acetate and 0.1% (wt/wt) ammonium-nitrogen as ammonium sulfate (final concentrations) not only resulted in the usual increase in autotrophic nitrifiers, but also in a fourfold increase in the heterotrophic nitrifying Arrthrobacter. Amendment of like samples with N-Serve [2-chloro-6(trichloromethyl) pyridinel] prevented the increase in Nitrosomonas, but not that in the heterotrophic nitrifiers. Nitrate production in the presence of the inhibitor was diminished but not prevented. An Arthrobacter sp., isolated from the muck, produced nitrite when inoculated at high densities into sterile soil, unamended or amended with sodium acetate and/or ammomium sulfate. These data suggest that the heterotrophic population may be responsible for some of the nitrate produced in these Histosols.

Acetates↗