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 145 records · Page 8Linked to original sources
PubMed2003

[Study on ability of nitrification in a subsurface constructed wetland system treating sewage].

The nitrification ability of different layers in a subsurface constructed wetland treating sewage was measured. The experiment results showed that the ability of nitrification was decreased along the direction of water flow in the subsurface wetland. The constants of ammonia oxidation rate and nitrite oxidation rate in the slag layer on the bottom were 1.99-6.89 mg.(h.kg)-1 and 1.14-5.22 mg.(h.kg)-1 respectively, but in the soil layer on the top were 0.53-0.89 mg.(h.kg)-1 and 0.96-1.39 mg.(h.kg)-1 respectively. So the ability of nitrification in the layer of slag was better than the layer of soil obviously, and it showed that the nitrification was mainly happened in the slag layer.

Ammonia↗
PubMed2004

The presence of ammonium facilitates nitrite reduction under PHB driven simultaneous nitrification and denitrification.

For economic and efficient nitrogen removal from wastewater treatment plants via simultaneous nitrification and denitrification the nitrification process should stop at the level of nitrite such that nitrite rather than nitrate becomes the substrate for denitrification. This study aims to contribute to the understanding of the conditions that are necessary to improve nitrite reduction over nitrite oxidation. Laboratory sequencing batch reactors (SBRs) were operated with synthetic wastewater containing acetate as COD and ammonium as the nitrogen source. Computer controlled operation of the reactors allowed reproducible simultaneous nitrification and denitrification (SND). The oxygen supply was kept precisely at a low level of 0.5 mgL(-1) and bacterial PHB was the only electron donor available for denitrification. During SND little nitrite or nitrate accumulated (< 20% total N), indicating that the reducing processes were almost as fast as the production of nitrite and nitrate from nitrification. Nitrite spiking tests were performed to investigate the fate of nitrite under different oxidation (0.1-1.5 mgL(-1) of dissolved oxygen) and reduction conditions. High levels of reducing power were provided by allowing the cells to build up to 2.5 mM of PHB. Nitrite added was preferentially oxidised to nitrate rather than reduced even when dissolved oxygen was low and reducing power (PHB) was excessively high. However, the presence of ammonium enabled significant reduction of nitrite under low oxygen conditions. This is consistent with previous observations in SBR where aerobic nitrite and nitrate reduction occurred only as long as ammonium was present. As soon as ammonium was depleted, the rate of denitrification decreased significantly. The significance of the observed strongly stimulating effect of ammonium on nitrite reduction under SND conditions is discussed and potential consequences for SBR operation are suggested.

Acetates↗
PubMed2005

[Nitrification and denitrification in the integrated vertical flow constructed wetlands].

Nitrification and denitrification in the different layers of the integrated vertical flow constructed wetlands (IVCW) are studied. The results show the constants rate of nitrification and denitrification in the strata of IVCW were 0.01 - 6.35microg x (gxd)-1 and 3.37 - 4.19microg x (gxd)-1 respectively. The most probable number (MPN) method are employed to determine the number and distribution of nitrifying and denitrifying bacteria in the strata of the system. The results show that the numbers of nitrifying and denitrifying bacteria were 7.5 x 10(3) - 1.1 x 10(5) MPN x g(-1) and 7.5 x 10(6) - 1.1 x 10 MPN x g(-1) respectively. The positive correlation between bacteria and their action was obvious (r = 0.9661, p < 0.001, r = 0.7722, p < 0.025). It is also observed that the number of nitrifying bacteria and nitrification rate was decreased along the direction of the water in the IVCW, while denitrifying bacteria and denitrification rate was increased. And there was the significant negative correlation between nitrification and denitrification rate(r = -0.9776, p < 0.001).

Biodegradation, Environmental↗
PubMed1990

[Examination of sewage for nitrification inhibitors with the help of a simple and accessible bioassay].

The biotest presented permits the investigation of sewage as for the presence of nitrification-inhibiting substances. A waste-water sample has to be aerated together with activated sludge for 5 h. The concentration of ammonia and nitrate will be analysed at the beginning and the end of the test. The intensity of nitrification can be detected comparing the increase of nitrate in the sewage sample with a control. In order to verify the reliance of the test the effect of different parameters on the test system like pH, BOD of the sludge, content of ammonia, nitrite and nitrate and different sewage-relevant compounds were investigated. The biotest was successfully applied in order to find out the inhibition of nitrification in a communal purification plant. An emission of nitrification inhibiting substances was determined by screening of the supplies of the purification plant.

Ammonia↗
PubMed1985

Influence of the herbicides Goltix and Sencor on nitrification process in two soils.

The effects of two herbicides, Sencor and Goltix, on nitrification in two soils were studied using a mixed culture of nitrifying bacteria. Sencor (10 ppm, 50 ppm, and 100 ppm) has no inhibitory influence on nitrification. In the presence of 50 ppm and 100 ppm Goltix the nitrification process is not affected but in the presence of 500 ppm Goltix ammonium oxidation is considerably retarded. In sandy loam field soil (pH 7.1) the retarding effect was more pronounced than in silty loamy sand (pH 7.8) of meadow. 500 ppm Goltix has a more lasting inhibitory effect on ammonium oxidation than some commercially available nitrification inhibitors.

Ammonia↗
PubMedDate not supplied

High nitrite buildup during nitrification in a rotating disk reactor.

Incomplete nitrification with high nitrite accumulation has three practical advantages: lower oxygen consumption, less need for organics for denitrification, and lower sludge production during denitrification. Nitrification leading to high nitrite formation was experimentally studied in a continuous single rotating disk reactor (RDR) and compared to a modeled continuous completely stirred tank reactor (CSTR). The results of this model show that to accumulate nitrite greater than 50% at oxygen levels higher than 3.5 mg O2/L, pH levels higher than 8.5 and 9.0 are required for a CSTR with and without cell washout, respectively. For a CSTR without cell washout at pH 7 and 1 mg O2/L, it was predicted that a nitrite accumulation less than 5% could be reached. Conversely, for a partially submerged continuous RDR without any additional aeration supply (already at pH 7 and 1.3 mg O2/L), high nitrite accumulation (more than 75%) was achieved and the influence of pH from 7 to 9 was not significant. This difference is believed to be caused by mass transfer. In addition, nitrification was observed to occur under oxygen transport limitation for a totally submerged continuous RDR.

Bioreactors↗
PubMed2003

Simultaneous nitrification and denitrification using stored substrate (PHB) as the electron donor in an SBR.

The potential for PHB (poly-beta-hydroxybutyrate) to serve as the electron donor for effective simultaneous nitrification and denitrification (SND) was investigated in a 2-L sequencing batch reactor (SBR) using a mixed culture and acetate as the organic substrate. During the feast period (i.e., acetate present), heterotrophic respiration activity was high and nitrification was prevented due to the inability of nitrifying bacteria to compete with heterotrophs for oxygen. Once acetate was depleted the oxidation rate of PHB was up to 6 times slower than that of soluble acetate and nitrification could proceed due to the decreased competition for oxygen. The slow nature of PHB degradation meant that it was an effective substrate for SND, as it was oxidised at a similar rate to ammonium and was therefore available for SND throughout the entire aerobic period. The percentage of nitrogen removed via SND increased at lower DO concentrations during the famine period, with up to 78% SND achieved at a DO concentration of 0.5 mg L(-1). However, the increased percentage of SND at a low DO concentration was compromised by a 2-times slower rate of nitrogen removal. A moderate DO concentration of 1 mg L(-1) was optimal for both SND efficiency (61%) and rate (4.4 mmol N x Cmol x(-1) x h(-1)). Electron flux analysis showed that the period of highest SND activity occurred during the first hour of the aerobic famine period, when the specific oxygen uptake rate (SOUR) was highest. It is postulated that a high SOUR due to NH(4) (+) and PHB oxidation decreases oxygen penetration into the floc, creating larger zones for anoxic denitrification. The accumulation of nitrate towards the end of the SND period showed that SND was finally limited by the rate of denitrification. As PHB degradation was found to follow first-order kinetics (df(PHB)/dt = -0.19 x f(PHB)), higher PHB concentrations would be expected to drive SND faster by increasing the availability rate of reducing power and reducing penetration of oxygen into the floc, due to the corresponding increased SOUR. Process control techniques to accumulate higher internal PHB concentrations to improve PHB-driven SND are discussed.

Aerobiosis↗
PubMed2003

Effect of oxygen concentration on nitrification and denitrification in single activated sludge flocs.

Simultaneous nitrification and denitrification (SND) was investigated in the single aeration tank of a municipal wastewater treatment plant. Microelectrode measurements and batch experiments were performed to test for the presence of SND. Microelectrodes recorded the presence of O(2) concentration gradients in individual activated sludge flocs. When the O(2) concentration in the bulk liquid was <45 microM, anoxic zones were detected within flocs with a larger diameter (approximately 3000 microm). The O(2) penetration depth in the floc was found to be dependent on the O(2) concentration in the bulk liquid. Nitrification was restricted to the oxic zones, whereas denitrification occurred mainly in the anoxic zones. The nitrification rate of the activated sludge increased with increasing O(2) concentration in the bulk liquid, up to 40 microM, and remained constant thereafter. SND was observed in the aerated activated sludge when O(2) concentration was in the range of 10 to 35 microM.

Biodegradation, Environmental↗
PubMed2003

Simultaneous nitrification, denitrification, and phosphorus removal in a lab-scale sequencing batch reactor.

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic-enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the energy and COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen (DO) concentration (0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification, and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHAs), accompanied by phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to <0.5 mg/L by the end of the cycle. Ammonia was also oxidized during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis showed that the final denitrification product was mainly nitrous oxide (N(2)O), not N(2). Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms (DGAOs), rather than denitrifying polyphosphate-accumulating organisms (DPAOs), were responsible for the denitrification activity.

Acetic Acid↗
PubMed2001

Use of a novel nitrification inhibitor to reduce nitrous oxide emission from (15)N-labelled dairy slurry injected into soil.

Recent recommendations for environmentally sound use of liquid animal manure often include injection of slurry into soil. Two of the most important undesired side effects, ammonia (NH(3)) volatilisation and odour emissions, are usually significantly reduced by slurry injection. On the other hand, because of the higher amount of nitrogen (N) remaining in soil, the risk of nitrate (NO(3)(-)) leaching and nitrous oxide (N(2)O) emissions is increased. Thus, the reduction of local effects caused by NH(3) deposition, e.g. N enrichment and soil acidification, may be at the cost of large-scale effects such as ozone depletion and global warming as a result of emitted N(2)O. In this context, nitrification inhibitors can contribute significantly to a reduction in NO(3)(-) leaching and N(2)O production. A field experiment was carried out at IGER, North Wyke, which aimed to evaluate the effect of the new nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP/ENTEC). For this experiment, (15)N enriched dairy slurry was used and the isotopic label in soil N as well as in N(2)O were studied. After slurry injection into the grassland soil in August 2000, the major emissions of N(2)O occurred during the first ten days. As expected, high N(2)O emission rates and (15)N content of the emissions were concentrated on the slurry injection slots, showing a steep decrease towards the untreated centre-point between slurry injection slots. The nitrification inhibitor DMPP proved to be very efficient in reducing N(2)O emissions. At a rate of 2 kg DMPP ha(-1), the total amount of N(2)O emitted was reduced by 32%, when compared with slurry injection without DMPP. The isotopic label of the emitted N(2)O showed that during the 22-day experimental period, emissions from the slurry N pool were strongly reduced by DMPP from 0.93 kg N(2)O-N ha(-1) (-DMPP) to 0.50 kg N(2)O-N ha(-1) (+DMPP), while only a minor effect on emissions from the soil N pool was observed (0.69 to 0.60 kg N(2)O-N ha(-1); -DMPP, +DMPP, respectively).

Algorithms↗
PubMed1995

The toxicity of substituted phenols in the nitrification inhibition test and luminescent bacteria test.

The nitrification inhibition test and the luminescent bacteria test were used to determine the inhibiting effect of different phenolic compounds. The chlorinated phenols demonstrated an increased toxicity in the nitrification inhibition test, which was much more sensitive to these compounds than other bacterial toxicity tests. In practice, the nitrification inhibition test was very useful for estimating the toxicity of chemical compounds to nitrifying bacteria, but the test is not recommended for the assessment of general bacterial toxicity. In comparison to other bacterial toxicity tests, the luminescent bacteria test also proved to be very sensitive. Due to its character, which measures a certain physiological parameter, this test system could be used as a screening tool for possible inhibitory effects to bacteria, although positive results should be confirmed by other bacterial toxicity tests.

Ammonium Sulfate↗
PubMed1979

Effect of soil microstructure on the relationship between the intensity of nitrification and soil moisture.

The relationship between the logarithm of nitrification intensity and moisture (expressed as pF) did not have an ideal linear course in structural soils in which pores of a certain size predominated. When increasing the incubation moisture it could be observed that the intensity of nitrification decreases at pF 3.5-4.4 and increases again on further increasing the incubation moisture. The detected anomaly was observed when applying moistures corresponding to peaks of derivation pF-curves. It can be assumed that the relationship between the intensity of nitrification and moisture is modified by soil microstructure; therefore, this relationship was studied in more detail in the present communication.

Bacteria↗
PubMed2006

Biological nitrogen removal with nitrification and denitrification via nitrite pathway.

Presently, the wastewater treatment practices can be significantly improved through the introduction of new microbial treatment technologies. To meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of ammonium from wastewater have to be implemented. Partial nitrification to nitrite was reported to be technically feasible and economically favorable, especially when wastewater with high ammonium concentrations or low C/N ratios is treated. For successful implementation of the technology, the critical point is how to maintain partial nitrification of ammonium to nitrite. Partial nitrification can be obtained by selectively inhibiting nitrite oxidizing bacteria through appropriate regulation of the system's DO concentration, microbial SRT, pH, temperature, substrate concentration and load, operational and aeration pattern, and inhibitor. The review addressed the microbiology, its consequences for their application, the current status regarding application, and the future developments.

Bacteria↗
PubMed2004

Improved simultaneous nitrification and denitrification in a single reactor by using two different immobilization carriers with specific oxygen transfer characteristics.

To maximize nitrogen utilization rates during nitrification and denitrification in a simultaneous reaction for direct nitrogen removal from ammonia-nitrogen in a single reactor, two different carriers were applied that immobilized nitrifiers and denitrifiers separately. With the optimized DO concentration and mixing ratio of immobilization carriers, ammonium-nitrogen was successfully removed as designed until the middle phase of treatment where nitrogen removal rate was higher than 83% of the theoretical value, although an imbalance between nitrification and denitrification occurred at a later phase of treatment where residual nitrate-nitrogen concentration was less than 2 mg/l. The new approach using two different carriers to immobilize nitrifiers and denitrifiers separately was proved useful for controlling both nitrification and denitrification rates, enabling the utilization of maximum treatment ability of both nitrifiers and denitrifiers in a single reactor for direct nitrogen removal from ammonium-nitrogen.

Acrylic Resins↗
PubMed2006

Factors affecting nitrous oxide production: a comparison of biological nitrogen removal processes with partial and complete nitrification.

Nitrous oxide (N(2)O) emission from biological nitrogen removal (BNR) processes has recently received more research attention. In this study, two lab-scale BNR systems were used to investigate the effects of various operating parameters including the carbon to nitrogen (C/N) ratio, ammonia loading, and the hydraulic retention time on N(2)O production. The first system was operated in a conventional BNR mode known as the Ludzack-Ettinger (LE) process, consisting of complete denitrification and nitrification reactors, while the second one was operated in a shortcut BNR (SBNR) mode employing partial nitrification and shortcut denitrification, which requires less oxygen and carbon sources. As the C/N ratio was decreased, a significant increase in N(2)O production was observed only in the anoxic reactor of the LE process, indicating that N(2)O was released as an intermediate of the denitrification reaction under the carbon-limited condition. However, the SBNR process did not produce significant N(2)O even at the lowest C/N ratio of 0.5. When the SBNR process was subjected to increasing concentrations of ammonia, N(2)O production from the aerobic reactor was rapidly increased. Furthermore, the increasing production of N(2)O was observed mostly in the aerobic reactor of the SBNR process with a decline in hydraulic retention time. These experimental findings indicated that the increase in N(2)O production was closely related to the accumulation of free ammonia, which was caused by an abrupt increase of the ammonium loading. Consequently, the partial nitrification was more susceptible to shock loading conditions, resulting in a high production of N(2)O, although the SBNR process was more efficient with respect to nitrogen removals as well as carbon and oxygen requirements.

Ammonia↗
PubMed2005

Effect of temperature and free ammonia on nitrification and nitrite accumulation in landfill leachate and analysis of its nitrifying bacterial community by FISH.

The cause of seasonal failure of a nitrifying municipal landfill leachate treatment plant utilizing a fixed biofilm was investigated by wastewater analyses and batch respirometric tests at every treatment stage. Nitrification of the leachate treatment plant was severely affected by the seasonal temperature variation. High free ammonia (NH3-N) inhibited not only nitrite oxidizing bacteria (NOB) but also ammonia oxidizing bacteria (AOB). In addition, high pH also increased free ammonia concentration to inhibit nitrifying activity especially when the NH4-N level was high. The effects of temperature and free ammonia of landfill leachate on nitrification and nitrite accumulation were investigated with a semi-pilot scale biofilm airlift reactor. Nitrification rate of landfill leachate increased with temperature when free ammonia in the reactor was below the inhibition level for nitrifiers. Leachate was completely nitrified up to a load of 1.5 kg NH4-N m(-3)d(-1) at 28 degrees C. The activity of NOB was inhibited by NH3-N resulting in accumulation of nitrite. NOB activity decreased more than 50% at 0.7 mg NH3-N L(-1). Fluorescence in situ hybridization (FISH) was carried out to analyze the population of AOB and NOB in the nitrite accumulating nitrifying biofilm. NOB were located close to AOB by forming small clusters. A significant fraction of AOB identified by probe Nso1225 specifically also hybridized with the Nitrosomonas specific probe Nsm156. The main NOB were Nitrobacter and Nitrospira which were present in almost equal amounts in the biofilm as identified by simultaneous hybridization with Nitrobacter specific probe Nit3 and Nitrospira specific probe Ntspa662.

Ammonia↗
PubMed2004

Challenges for simultaneous nitrification, denitrification, and phosphorus removal in microbial aggregates: mass transfer limitation and nitrous oxide production.

The microbial community composition and activity was investigated in aggregates from a lab-scale bioreactor, in which nitrification, denitrification and phosphorus removal occurred simultaneously. The biomass was highly enriched for polyphosphate accumulating organisms facilitating complete removal of phosphorus from the bulk liquid; however, some inorganic nitrogen still remained at the end of the reactor cycle. This was ascribed to incomplete coupling of nitrification and denitrification causing NO(3)(-) accumulation. After 2 h of aeration, denitrification was dependent on the activity of nitrifying bacteria facilitating the formation of anoxic zones in the aggregates; hence, denitrification could not occur without simultaneous nitrification towards the end of the reactor cycle. Nitrous oxide was identified as a product of denitrification, when based on stored PHA as carbon source. This observation is of critical importance to the outlook of applying PHA-driven denitrification in activated sludge processes.

Bacteria, Aerobic↗
PubMed2006

Osmotic stress on nitrification in an airlift bioreactor.

The effect of osmotic pressure on nitrification was studied in a lab-scale internal-loop airlift-nitrifying reactor. The reactor slowly adapted to the escalating osmotic pressure during 270 days operation. The conditions were reversed to the initial stage upon full inhibition of the process. Keeping influent ammonium concentration constant at 420 mg N L(-1) and hydraulic retention time at 20.7h, with gradual increase in osmotic pressure from 4.3 to 18.8x10(5) Pa by adding sodium sulphate, the ammonium removal efficiencies of the nitrifying bioreactor were maintained at 93-100%. Further increase in osmotic pressure up to 19.2x10(5) Pa resulted in drop of the ammonium conversion to 69.2%. The osmotic pressure caused abrupt inhibition of nitrification without any alarm and the critical osmotic pressure value causing inhibition remained between 18.8 and 19.2x10(5) Pa. Nitrite oxidizers were found more sensitive to osmotic stress as compared with ammonia oxidizers, leading to nitrite accumulation up to 61.7% in the reactor. The performance of bioreactor recovered gradually upon lowering the osmotic pressure. Scanning and transmission electron microscopy indicated that osmotic stress resulted in simplification of the nitrifying bacterial populations in the activated sludge as the cellular size reduced; the inner membrane became thinner and some unknown inclusions appeared within the cells. The microbial morphology and cellular structure restored upon relieving the osmotic pressure. Addition of potassium relieved the effect of osmotic pressure upon nitrification. Results demonstrate that the nitrifying reactor possesses the potential to treat ammonium-rich brines after acclimatization.

Bioreactors↗