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 127 records · Page 7Linked to original sources
PubMed1986

Nitrification rates in the baltic sea: comparison of three isotope techniques.

Simultaneous measurements of nitrification in the Baltic Sea were made at 10- to 30-m intervals in the months of June and November by three isotope techniques: [N]nitrate dilution, N-serve sensitive [C]bicarbonate incorporation, and [N]ammonium oxidation to nitrite and nitrate. Nitrification rates of 1 to 280 nmol liter day were recorded, and each method showed that the highest rates of nitrification occurred below the halocline. Even in the presence of ammonium, dark incubations of mixed layer (above ca. 50 m) waters never yielded nitrification rates exceeding 45 nmol liter day. The rates measured by the ammonium oxidation method were two- to sevenfold greater than those obtained by C incorporation or N dilution. The merits of each technique are discussed, and it is suggested that the [N]ammonium oxidation method should be used in conjunction with the [C]bicarbonate incorporation method.

Journal Article↗
PubMed1991

Nitrification at Low pH by Aggregated Chemolithotrophic Bacteria.

A study was performed to gain insight into the mechanism of acid-tolerant, chemolithotrophic nitrification. Microorganisms that nitrified at pH 4 were enriched from two Dutch acid soils. Nitrate production in the enrichment cultures was indicated to be of a chemolithoautotrophic nature as it was (i) completely inhibited by acetylene at a concentration as low as 1 mumol/liter and (ii) strongly retarded under conditions of carbon dioxide limitation. Electron microscopy of the enrichment cultures showed the presence of bacteria that were morphologically similar to strains of known chemolithotrophic nitrifying genera. Many of the enriched bacteria, in particular those that were identified as ammonium oxidizers, were aggregated. Filtration experiments indicated that aggregated cells were able to nitrify at low pH, whereas single cells were not. It is hypothesized that cells inside the aggregates are protected against the toxicity of nitrous acid. Nitrification by aggregated chemolithoautotrophic bacteria may be the dominating process of nitrate formation in many acid soils as it does not appear to depend on the existence of microsites of high pH (acid-sensitive autotrophic nitrification) or on the availability of organic carbon (heterotrophic nitrification).

Journal Article↗
PubMed1993

Nitrification and denitrification in lake and estuarine sediments measured by the N dilution technique and isotope pairing.

The transformation of nitrogen compounds in lake and estuarine sediments incubated in the dark was analyzed in a continuous-flowthrough system. The inflowing water contained NO(3), and by determination of the isotopic composition of the N(2), NO(3), and NH(4) pools in the outflowing water, it was possible to quantify the following reactions: total NO(3) uptake, denitrification based on NO(3) from the overlying water, nitrification, coupled nitrification-denitrification, and N mineralization. In sediment cores from both lake and estuarine environments, benthic microphytes assimilated NO(3) and NH(4) for a period of 25 to 60 h after darkening. Under steady-state conditions in the dark, denitrification of NO(3) originating from the overlying water accounted for 91 to 171 mumol m h in the lake sediments and for 131 to 182 mumol m h in the estuarine sediments, corresponding to approximately 100% of the total NO(3) uptake for both sediments. It seems that high NO(3) uptake by benthic microphytes in the initial dark period may have been misinterpreted in earlier investigations as dissimilatory reduction to ammonium. The rates of coupled nitrification-denitrification within the sediments contributed to 10% of the total denitrification at steady state in the dark, and total nitrification was only twice as high as the coupled process.

Journal Article↗
PubMed1997

Stable-Isotope Analysis of a Combined Nitrification-Denitrification Sustained by Thermophilic Methanotrophs under Low-Oxygen Conditions.

To simulate growth conditions experienced by microbiota at O(inf2)-limited interfaces of organic matter in compost, an experimental system capable of maintaining dual limitations of oxygen and carbon for extended periods, i.e., a pO(inf2)-auxostat, has been used. (sup15)N tracer studies on thermophilic (53(deg)C) decomposition processes occurring in manure-straw aggregates showed the emission of dinitrogen gas from the reactor as a result of simultaneous nitrification and denitrification at low pO(inf2) values (0.1 to 2.0%, vol/vol). The N loss was confirmed by nitrogen budget studies of the system. Depending on the imposed pO(inf2), 0.6 to 1.4 mmol of N/day (i.e., 20 to 40% of input N) was emitted as N(inf2). When the pO(inf2) was raised, the rates of both nitrification and denitrification increased instantaneously, indicating that ammonia oxidation was limited by oxygen. In auxostats permanently running at pO(inf2) >= 2% (vol/vol), the free ammonium pool was almost completely oxidized and was converted to nitrite plus nitrate and N(inf2) gas. Labelling of the auxostat with [(sup13)C]carbonate was conducted to reveal whether nitrification was of autotrophic or heterotrophic origin. Incorporation of (sup13)CO(inf2) into population-specific cellular compounds was evaluated by profiling the saponifiable phospholipid fatty acids (FAs) by using capillary gas chromatography and subsequently analyzing the (sup13)C/(sup12)C ratios of the individual FAs, after their combustion to CO(inf2), by isotope ratio mass spectrometry. Apart from the observed label incorporation into FAs originating from a microflora belonging to the genus Methylococcus (type X group), supporting nitrification of a methylotrophic nature, this analysis also corroborated the absence of truly autotrophic nitrifying populations. Nevertheless, the extent to which ammonia oxidation continued to exist in this thermophilic community suggested that a major energy gain could be associated with it.

Journal Article↗
PubMed1999

Nitrification and autotrophic nitrifying bacteria in a hydrocarbon-polluted soil.

In vitro ammonia-oxidizing bacteria are capable of oxidizing hydrocarbons incompletely. This transformation is accompanied by competitive inhibition of ammonia monooxygenase, the first key enzyme in nitrification. The effect of hydrocarbon pollution on soil nitrification was examined in situ. In a microcosm study, adding diesel fuel hydrocarbon to an uncontaminated soil (agricultural unfertilized soil) treated with ammonium sulfate dramatically reduced the amount of KCl-extractable nitrate but stimulated ammonium consumption. In a soil with long history of pollution that was treated with ammonium sulfate, 90% of the ammonium was transformed into nitrate after 3 weeks of incubation. Nitrate production was twofold higher in the contaminated soil than in the agricultural soil to which hydrocarbon was not added. To assess if ammonia-oxidizing bacteria acquired resistance to inhibition by hydrocarbon, the contaminated soil was reexposed to diesel fuel. Ammonium consumption was not affected, but nitrate production was 30% lower than nitrate production in the absence of hydrocarbon. The apparent reduction in nitrification resulted from immobilization of ammonium by hydrocarbon-stimulated microbial activity. These results indicated that the hydrocarbon inhibited nitrification in the noncontaminated soil (agricultural soil) and that ammonia-oxidizing bacteria in the polluted soil acquired resistance to inhibition by the hydrocarbon, possibly by increasing the affinity of nitrifying bacteria for ammonium in the soil.

Colony Count, Microbial↗
PubMed2004

High-rate nitrification at low pH in suspended- and attached-biomass reactors.

This article reports on high-rate nitrification at low pH in biofilm and suspended-biomass reactors by known chemolithotrophic bacteria. In the biofilm reactor, at low pH (4.3 +/- 0.1) and low bulk ammonium concentrations (9.3 +/- 3.3 mg.liter(-1)), a very high nitrification rate of 5.6 g of N oxidized.liter(-1).day(-1) was achieved. The specific nitrification rate (0.55 g of N.g of biomass(-1).day(-1)) was similar to values reported for nitrifying reactors at optimal pH. In the suspended-biomass reactor, the average pH was significantly lower than that in the biofilm reactor (pH 3.8 +/- 0.3), and values as low as pH 3.2 were found. In addition, measurements in the suspended-biomass reactor, using isotope-labeled ammonium (15N), showed that in spite of the very low pH, biomass growth occurred with a yield of 0.1 g of biomass.g of N oxidized(-1). Fluorescence in situ hybridization using existing rRNA-targeted oligonucleotide probes showed that the nitrifying bacteria were from the monophyletic genus Nitrosomonas, suggesting that autotrophic nitrification at low pH is more widespread than previously thought. The results presented in this paper clearly show that autotrophic nitrifying bacteria have the ability to nitrify at a high rate at low pH and in the presence of only a negligible free ammonia concentration, suggesting the presence of an efficient ammonium uptake system and the means to cope with low pH.

Bacteria↗
PubMed1980

Sequential nitrification by an Alcaligenes sp. and Nitrobacter agilis.

The ecological importance of heterotrophic nitrification has been difficult to assess because of low levels of nitrification associated with this phenomenon. Nitrification by a soil isolate, an Alcaligenes sp., which oxidizes pyruvic oxime to produce up to 1867 mg nitrite-nitrogen/L, is described. Sequential nitrification with the chemoautotroph Nitrobacter agilis, ATCC 14123, resulted in nitrate accumulation and a concomitant decrease of the nitrite produced by the Alcaligenes sp. when the bacteria were jointly cultured. The ecological significance of such a sequential system is discussed.

Alcaligenes↗
PubMed1994

Effects of organic acids on heterotrophic nitrification by Alcaligenes faecalis OKK17.

Factors affecting heterotrophic nitrification by Alcaligenes faecalis OKK17, which was isolated from sewage sludge, were examined. Specific nitrifying activity increased as the pH increased up to 8.5. Most of the nitrogenous compounds (88%) in the culture supernatant were converted to hydroxylamine or nitrite at pH 9 but 87% of them remained as ammonium at pH 7. These results imply that the substrate for heterotrophic nitrification is ammonium and that the organism oxidizes ammonium to lower its toxic effect. Although the addition of acetate to a defined medium increased growth of the bacterium up to C/N = ca. 6, the accumulation of nitrification products almost paralleled the growth and the specific nitrifying activity decreased. Pyruvate and oxaloacetate increased the specific nitrifying activity six- to eightfold compared with the other organic acids examined, but the key enzyme activities in the glyoxylate cycle were not increased. Acetate, glyoxylate, and malonate did not increase the specific nitrifying activity, but they increased the enzyme activities. These results imply that the involvement of acetate metabolism in the heterotrophic nitrification is unlikely.

Acetates↗
PubMed2006

Nitrous oxide nitrification and denitrification 15N enrichment factors from Amazon forest soils.

The isotopic signatures of 15N and 18O in N2O emitted from tropical soils vary both spatially and temporally, leading to large uncertainty in the overall tropical source signature and thereby limiting the utility of isotopes in constraining the global N2O budget. Determining the reasons for spatial and temporal variations in isotope signatures requires that we know the isotope enrichment factors for nitrification and denitrification, the two processes that produce N2O in soils. We have devised a method for measuring these enrichment factors using soil incubation experiments and report results from this method for three rain forest soils collected in the Brazilian Amazon: soil with differing sand and clay content from the Tapajos National Forest (TNF) near Santarém, Pará, and Nova Vida Farm, Rondônia. The 15N enrichment factors for nitrification and denitrification differ with soil texture and site: -111 per thousand +/- 12 per thousand and -31 per thousand +/- 11 per thousand for a clay-rich Oxisol (TNF), -102 per thousand +/- 5 per thousand and -45 per thousand +/- 5 per thousand for a sandier Ultisol (TNF), and -10.4 per thousand +/- 3.5 per thousand (enrichment factor for denitrification) for another Ultisol (Nova Vida) soil, respectively. We also show that the isotopomer site preference (delta15Nalpha - delta15Nbeta, where alpha indicates the central nitrogen atom and beta the terminal nitrogen atom in N2O) may allow differentiation between processes of production and consumption of N2O and can potentially be used to determine the contributions of nitrification and denitrification. The site preferences for nitrification and denitrification from the TNF-Ultisol incubated soils are: 4.2 per thousand +/- 8.4 per thousand and 31.6 per thousand +/- 8.1 per thousand, respectively. Thus, nitrifying and denitrifying bacteria populations under the conditions of our study exhibit significantly different 15N site preference fingerprints. Our data set strongly suggests that N2O isotopomers can be used in concert with traditional N2O stable isotope measurements as constraints to differentiate microbial N2O processes in soil and will contribute to interpretations of the isotopic site preference N2O values found in the free troposphere.

Brazil↗
PubMed2001

Potential nitrification rate as a tool for screening toxicity in metal-contaminated soils.

A potential nitrification rate test (PNR) was used to identify metal toxicity in field-contaminated soils. The test was applied to metal salt-spiked soils, to 27 uncontaminated soils, and to 15 soils that are contaminated by former metal smelting activities. Four agricultural soils (pH 4.5-6.6) were spiked with various rates of CdCl2 (0-200 mg Cd/kg dry wt) or ZnCl2 (0-3,000 mg Cd/kg dry wt) and were equilibrated more than nine months prior to testing. The soil Zn EC50s of the PNR were between 150 and 350 mg Zn/kg dry weight. No continuous decrease of the nitrification with increasing Cd application was observed. The nitrification rate was reduced by between 50 and 80% at the highest Cd application in all soils. The PNRs of 27 uncontaminated soils varied widely (0-21 mg N/kg/d), but most of this variability is explained by soil pH (R2 = 0.77). The PNRs of the 15 contaminated soils were 0 to 44% of the values predicted for an uncontaminated soil at corresponding pH. Significant toxicity in field-contaminated soils was identified if the PNR was outside the 95% prediction interval of the PNR for an uncontaminated soil at corresponding pH and was found in seven soils. These soils contain 160 to 34,000 mg Zn/kg dry weight and 5 to 104 mg Cd/kg dry weight and had a pH >5.7. No toxicity could be detected below pH 5.6, where even a zero PNR value is within the 95% prediction interval of uncontaminated soils. It is concluded that the nitrification is sensitive to metal stress but that its power as a soil bioassay is low because of the high variability of the endpoint between uncontaminated soils. The ecological significance of the assay is discussed.

Environmental Monitoring↗
PubMed2006

High-rate nitrification using aerobic granular sludge.

The performance of nitrifying granules, which had been produced in an aerobic upflow fluidised bed (AUFB) reactor, was investigated in various types of ammonia-containing wastewaters. When pure oxygen was supplied to the AUFB reactor with a synthetic wastewater containing a high concentration of ammonia (500 g-N/m3), the ammonia removal rate reached 16.7 kg-N/m3/day with a sustained ammonia removal efficiency of more than 80%. The nitrifying granules possessing a high settling ability could be retained with a high density (approximately 10,000 g-MLSS/m3) in a continuous stirring tank reactor (CSTR) even under a short hydraulic retention time (44 min), which enabled a high-rate and stable nitrification for an inorganic wastewater containing low concentrations of ammonia (50 g-N/m3). Moreover, the nitrifying granules exhibited sufficient performance in the nitrification of real industrial wastewater containing high concentrations of ammonia (1000-1400 g-N/m3) and salinity (1.2-2.2%), which was discharged from metal-refinery processes. When the nitrifying granules were used in cooperation with activated sludge to treat domestic wastewater containing organic pollutants as well as ammonia, they fully contributed to nitrification even though a part of activated sludge adhered onto the granule surfaces to form biofilms. These results show the wide applicability of nitrifying granules to various cases in the nitrification step of wastewater treatment plants.

Ammonia↗
PubMed2006

Multistage wastewater treatment using separated storage driven denitrification and nitrification biofilms.

The feasibility of combining a previously reported storage driven denitrification biofilm, where 80% of influent acetate can be converted to poly-beta-hydroxybutyrate (PHB), with a suitable nitrification reactor, either submerged or trickling filter design, to achieve complete biological nitrogen removal was tested. The reactor system showed the potential of complete biological nitrogen removal of waste streams with a C/N ratio as low as 3.93 kg COD/kg N-NH3 at an overall nitrogen removal rate of 1.1 mmole NH3/L/h. While the efficiency and the rates of nitrogen removal were higher than what is observed in traditional or simultaneous nitrification and denitrification (SND) systems, there were two problems that require further development: (a) the incomplete draining of the reactor caused ammonia retention and release in the effluent, limiting the overall N-removal and (b) pH drifts in the nitrification step slowed down the rate of nitrification if not corrected by appropriate pH adjustment or buffering.

Ammonia↗
PubMed1997

[Isolation of bacteria which could perform nitrification and denitrification simultaneously by gene probe].

The bacteria which could perform nitrification and denitrification simultaneously from nitrogen containing wastes in Taiwan were isolated by using the probes made from random DNA fragments of Thiosphaera pantotropha. Two isolates were identified and named Alcaligenes faecalis subsp. faecalis strain 1 and strain 2 respectively. The effects on nitrification and denitrification by different medium pH, oxygen content, addition of different electron donors or inhibitors were studied. The isolates not only could perform nitrification, but also denitrification even in the presence of oxygen. Potassium cyanide could inhibit denitrification; hydrazine and hydroxyamine could inhibit nitrification. Alcaligenes faecalis subsp. faecalis strain 2 shows better denitrification.

Alcaligenes↗
PubMed2000

Heterotrophic nitrification by a thermophilic Bacillus species as influenced by different culture conditions.

The nitrification activity of a thermophilic heterotrophic bacterium, Bacillus MS30 isolated from a deep-sea hydrothermal vent, was studied under various growth conditions. Nitrification was estimated from the nitrogen balance calculations in the culture media. The results showed that this isolate actively nitrified in culture conditions similar to those prevailing in hydrothermal sites. Therefore, its ecological significance was considered. In standard aerobic conditions, MS30 produced nitrite from ammonia and acetate (1.13 mumol NO2-.mg-1 dry wt), but nitrate was never produced, and a low nitrite reduction was often observed. Higher nitrification activities were observed in defined optimal conditions (simple carbon substrate, 65 degrees C, pH 7.5, and 15 g sea salts.L-1). In addition, discrepancies between the optima for growth and nitrification were observed, showing the ability of MS30 to adapt to changing environmental conditions typical of hydrothermal sites.

Ammonia↗
PubMed2001

Impact of seeding with nitrifying bacteria on nitrification process efficiency.

Seeding of nitrifying bacteria into the activated sludge process was studied both theoretically and experimentally. A simple model was developed for prediction of the effects of seeding of nitrifying bacteria from a separate stage into the activated sludge process. The purpose of seeding is to improve the treatment results and the process stability as well as to decrease the volume requirements of the process. Pilot plant studies were carried out at the Uppsala municipal wastewater treatment plant in order to evaluate the effects of seeding. One line was supplied with supernatant from dewatering of digested sludge and the nitrification process gave an activated sludge with a high fraction of nitrifying bacteria, suitable for seeding. The other line was supplied with pre-precipitated wastewater and with the excess sludge from the line treating the supernatant. The experimental results showed that nitrification could be obtained at sludge ages that would otherwise preclude nitrification. Performance relationships for the system developed, based on laboratory and on-line measurements were studied and are presented. The studies show that seeding may decrease the necessary volume needs for a stable nitrification process and that the effects could be predicted by use of a simple model.

Bacteria↗
PubMed2001

Increasing the fertilizer value of palm oil mill sludge: bioaugmentation in nitrification.

Malaysia is essentially an agricultural country and her major polluting effluents have been from agro-based industries of which palm oil and rubber industries together contribute about 80% of the industrial pollution. Palm oil sludge, commonly referred to, as palm oil mill effluent (POME) is brown slurry composed of 4-5% solids, mainly organic, 0.5-1% residual oil, and about 95% water. The effluent also contains high concentrations of organic nitrogen. The technique for the treatment of POME is basically biological, consisting of pond systems, where the organic nitrogen is converted to ammonia, which is subsequently transformed to nitrate, in a process called nitrification. A 15-month monitoring program of a pond system (combined anaerobic, facultative, and aerobic ponds in series) confirmed studies by other authors and POME operators that nitrification in a pond system demands relatively long hydraulic retention time (HRT), which is not easily achieved, due to high production capacity of most factories. Bioaugmentation of POME with mixed culture of nitrifiers (ammonia and nitrite oxidizers) has been identified as an effective tool not only for enhancing nitrification of POME but also for improving quality of POME as source of liquid nitrogen fertilizer for use in the agricultural sector, especially in oil palm plantations. Nitrate is readily absorbable by most plants, although some plants are able to absorb nitrogen in the form of ammoniun. In this study, up to 60% reduction in HRT (or up to 20% reduction in potential land requirement) was achieved when bioaugmentation of POME was carried out with the aim of achieving full nitrification.

Agriculture↗
PubMed2002

[Using a two-stage SBR process for removal of organics and nitrification-denitrification via nitrite].

High efficiency removal of organics and nitrogen by using a two-stage SBR process was introduced in this paper. Most of organics was removed in the first stage SBR reactor(SBR1) under the aerobic condition. Subsequently the second stage SBR reactor(SBR2) firstly operated under the aerabic condition for simultaneous nitrification and removal of a small amount of residual organics. Nitrification was controlled to the nitrite-type nitrification. Then denitrification happened in SBR2 under the anoxic condition. The petrochemical industry wastewater was used as external carbon sources in the denitrification. The experimental results indicated that in a two-stage SBR system, two kinds of biomass with the different function existed in the different reactors, which was beneficial to improve the treatment efficiency. The effluent COD reduced again because SBR2 removed COD which was left in SBR1 effluent. It resisted the disturbance of the high organic loading to nitrification. Consequently, as compared to a single SBR process, a two-stage SBR not only improved the treatment efficiency, but also saved the energy cost.

Industrial Waste↗
PubMed2002

Two stage activated sludge plants--influence of different operational modes on sludge bulking and nitrification.

Conventional two stage activated sludge plants often lack sufficient nutrient removal performance due to substrate limitation for denitrification in the second stage. For the extension of the Vienna Main WWTP a two stage concept has been developed and tested by means of a pilot plant (scale 1:10.000). The new concept enables the operation of two different modes: In BYPASS-mode a portion of the primary clarifier effluent is fed directly to the second stage; the HYBRID-mode includes the exchange of mixed liquor between the two stages; over the course of the pilot plant investigations it turned out that nutrient removal is strongly increased in comparison to conventional two stage mode, but the two modes of operation lead to different results with regard to the sludge quality and the nitrification performance. BYPASS mode yields a higher SVI in both stages and a lower nitrification performance in comparison to HYBRID mode. This is caused by the negative influence of the primary effluent on the biocoenosis of the second stage. Additionally, the reduced sludge loading of the first stage in this mode results in a higher sludge age which favours the growth of filaments (Microthrix and Nocardia). In HYBRID-mode the higher load of the first stage results in a lower sludge age, fatty components are metabolized and incorporated in the sludge, thus, the growth of filaments is significantly reduced. Additionally, nitrification inhibiting substances are degraded in the first stage, which results in a higher nitrification performance in the second stage.

Actinobacteria↗