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1.
A lab-scale sequencing batch reactor was operated with alternating anoxic/aerobic conditions for nitrogen removal. Flocs and granules co-existed in the same reactor, with distinct aggregate structure and size, for over 180 days of reactor operation. Process data showed complete nitrogen removal, with temporary nitrite accumulation before full depletion of ammonia in the aerobic phase. Microbial quantification of the biomass by fluorescence in situ hybridisation showed that granules contained most of the nitrite-oxidising bacteria (NOB) whereas the ammonium-oxidising bacteria (AOB) seemed to be more abundant in the flocs. This was supported by microsensor measurements, which showed a higher potential of NO 2− uptake than NH 4 uptake in the granules. The segregation is possibly linked to the different growth rates of the two types of nitrifiers and the reactor operational conditions, which produced different sludge retention time for flocs and granules. The apparent physical separation of AOB and NOB in two growth forms could potentially affect mass transfer of NO 2− from AOB to NOB, but the data presented here shows that it did not impact negatively on the overall nitrogen removal. 相似文献
2.
Laboratory-scale experiments were conducted to examine the N 2O emission during the denitrification process. For each of the 6 runs carried out, synthetic effluent was fed in a 10 l batch mixed liquor to investigate the effect of nitrite on N 2O emission and Helium was continuously bubbled through the reactor at constant rate (0.12 l/min) to favour N 2O transfer and detection. An increasing COD/NO 3−-N influent ratio from 3 to 7 was firstly applied (runs 1–3). Secondly, NO 2− pulse additions were performed during run 4 and 5 (10 and 20 mg N/l, respectively). Finally, the reactor was fed with influent containing both NO 2− and NO 3−. We showed that N 2O emission was detected shortly after NO 2− accumulation, few minutes after the substrate feeding. The highest emission occurred at the lower COD/NO 3−-N ratio (=3) and at the higher NO 2− addition (20 mg N/l). In addition, the higher nitrogen conversion to N 2O gas (14.4%) was obtained with an influent containing initially both NO 2− and NO 3−. Our results suggest a direct effect of the NO 2− concentration on the N 2O emission. We have also confirmed the inhibitory effect of NO 2− concentration on N 2O reduction. 相似文献
3.
The perchlorate (ClO 4−)-respiring organism, strain perc1ace, can grow using nitrate (NO 3−) as a terminal electron acceptor. In resting cell suspensions, NO 3− grown cells reduced ClO 4−, and ClO 4− grown cells reduced NO 3−. Activity assays showed that nitrate reductase (NR) activity was 1.31 μmol min −1 (mg protein) −1 in ClO 4− grown cells, and perchlorate reductase (PR) activity was 4.24 μmol min −1 (mg protein) −1 in NO 3− grown cells. PR activity was detected within the periplasmic space, with activities as high as 14 μmol min −1 (mg protein) −1. The NR had a pH optimum of 9.0 while the PR had an optimum of 8.0. This study suggests that separate terminal reductases are present in strain perclace to reduce NO 3− and ClO 4−. 相似文献
4.
A procedure is described for preparing particles from cells of Micrococcus denitrificans which were broken osmotically after treatment with lysozyme. 1. 1. The preparations catalysed ATP synthesis coupled to O2 uptake or NO3− reduction. With NADH or succinate as the electron donors the P:O ratios were about 1.5 and 0.5, respectively; and the P:NO3− ratios were about 0.9 and 0.06, respectively. 2. 2. Addition of ADP or Pi to the reaction mixture increased the rates of NADH-dependent O2 uptake and NO3− reduction. Addition of 1 mM 2,4-dinitrophenol, which inhibited phosphorylation by 50–60%, increased the basal rates of electron transport. 3. 3. Evidence derived from spectrophotometry and from the differential inhibition by antimycin A of O2 and NO3− reduction leads to the conclusion that the nitrate reductase interacted with the respiratory chain in the region of the b-type cytochrome, and that the c-type cytochrome present was not involved in the reduction of NO3− to NO2−.
Abbreviations: TMPD; tetramethyl-p-phenylenediamine 相似文献
5.
A novel nutrient removal/waste heat utilization process was simulated using semicontinuous cultures of the thermophilic cyanobacterium Fischerella. Dissolved inorganic carbon (DIC)-enriched cultures, maintained with 10 mg l −1 daily productivity, diurnally varying temperature (from 55°C to 26–28°C), a 12:12 light cycle (200 μE sec −1 m −2) and 50% biomass recycling into heated effluent at the beginning of each light period, removed > 95% of NO 3− + NO 2−−N, 71% of NH 3-N, 82% of PO 43− −P, and 70% of total P from effluent water samples containing approximately 400 μg l −1 combined N and 60 μg l −1 P. Nutrient removal was not severely impaired by an altered temperature gradient, doubled light intensity, or DIC limitation. Recycling 75% of the biomass at the end of each light period resulted in unimpaired NO 3− + NO 2− removal, 38–45% P removal and no net NH 3 removal. Diurnally varying P removal, averaging 50–60%, and nearly constant > 80% N removal, are therefore projected for a full-scale process with continuous biomass recycling. 相似文献
6.
The concentrations of suspended solids, nitrogen (NH 4+, NO 3−, NO 2−), phosphorus (total phosphorus, PO 4−3) and silicate were measured in water ebbing from seagrass-covered tidal mudflats and from adjacent ungrassed mudflats in Western Port, Victoria, Australia. Ebb water was collected on six occasions during January and February (summer) and once during July (winter). From both types of mudflats the concentrations of suspended solids, phosphorus and silicate increased during the last hour of ebb tide with maxima in concentrations reached 0.5 to 1 h before slack water ebb. During the last 1.5–2.5 h of ebb tide the suspended solids, phosphorus and silicate concentrations were higher in water ebbing from denuded mudflats than from seagrass-covered mudflats. The concentration of nitrogen remained low in water ebbing from both types of mudflats during the day, but increased significantly during a night-time ebb; light-dependent biological uptake of nitrogen is implicated. It is suggested that denudation of seagrass-covered tidal mudflats would lead to increased efflux of suspended solids, phosphorus and silicate from sediments to overlying water. 相似文献
7.
1. The nitrite oxidase particles obtained by sonic oscillation of Nitrobacter agilis cells also possessed appreciable formate oxidase activity, ranging from about 25 to 50% of the nitrite oxidase activity depending upon the N. agilis strain. Both activities distributed themselves in the same pattern and proportions during differential centrifugation, and resided solely in the pellet resulting from high-speed centrifugation. 2. Difference spectra of formate-reduced particles or intact cells demonstrated the presence of cytochromes of the c- and a-types like those of the NO2−-reduced material. Under anaerobic conditions NO3− or fumarate acted as an alternate electron acceptor in place of O2 in formate oxidation. Under aerobic conditions increasing NO3− concentrations resulted in (a) an increased role of NO3− as a terminal electron acceptor compared to O2, (b) a greater total enzymatic transfer of electrons from formate than if O2 were the sole electron acceptor, and (c) a partial inhibition of O2 uptake suggestive of a competition for electrons by the two acceptors. The formate oxidase system failed to catalyze consistently the transfer of electrons to either added mammalian cytochrome c or Fe(CN)63−. The marked sensitivity of the system to certain inhibitors implicated cytochrome oxidase as an integral part of the formate oxidase. The system was also inhibited significantly by a variety of chelating agents, indicating a metal component in the formate dehydrogenase or early portion of the electron transfer sequence. 3. The stoichiometry of the formate oxidase system was shown to approach the theoretical value of 2 moles of CO2 evolved per mole of O2 or per 2 moles of formate consumed. 4. To a limited extent, phosphorylation occurred concomittantly with the oxidation of formate in the presence of the cell-free particulate system. 相似文献
8.
Two irrigation systems were used to compare nitrogen uptake efficiency in citrus trees and to evaluate the NO 3− runoff in «Navelina» orange trees [ Citrus sinensis (L.) Osbeck] on Carrizo citrange rootstock ( Citrus sinensis × Poncirus trifoliata Raf.). These were fertilized with 125 g N as labelled K 15NO 3 and grown outdoors in containers filled with a sand-loamy soil. Two groups of 3 trees received this N dose either in five equally split applications by a flooding irrigation system or in 66 applications by drip. Trees were harvested at the end of the vegetative cycle (December) and the isotopic ratios of 15N/ 14N were measured in the soil-plant system. The N uptake efficiency of the whole tree was higher with drip irrigation (75 percnt;) than with flooding system (64 percnt;). In the 0-90 cm soil profile, the N immobilized in the organic fraction was similar for both irrigation methods (around 13 percnt;), whereas the N retained as NO 3− was 1 percnt; of the N applied under drip and 10 percnt; under flooding. In the last case, most of NO 3− remained under root system and it could be lost to leaching either by heavy rainfalls or excessive water applications. These results showed that a drip irrigation system was more efficient for improving water use and N uptake from fertilizer, in addition to potentially reduced leaching losses. 相似文献
9.
A fed-batch process was developed for high cell density culture of the diatom Nitzschia laevis for enhanced production of eicosapentaenoic acid (EPA). Firstly, among the various medium components, glucose (Glu) was identified as the limiting substrate while nitrate (NO 3−), tryptone (Tr) and yeast extract (Ye) were found to promote cell growth by enhancing specific growth rate. Therefore, these components were considered essential and were included in the feed medium for subsequent fed-batch cultivation. With the optimized ratio of NO 3−:Tr:Ye being 1:2.6:1.3 (by weight), the relative proportions of glucose to the nitrogen sources in the feed were investigated. The optimal ratios of Glu:NO 3− for specific growth rate and EPA productivity were both determined to be 32:1 (by weight). Finally, based on the residual glucose concentration in the culture, a continuous medium feeding strategy for fed-batch fermenter cultivation was developed, with which, the maximal cell dry weight and EPA yield obtained were 22.1 g l −1 and 695 mg l −1, respectively, which were great improvements over those of batch cultures. 相似文献
10.
A field study measured the rate of soil mineral N supply and its effects on plant biomass and N accumulation in a 13-year-old, naturally regenerating, calcareous grassland. Gross rates of N mineralisation (2 μg g −1 day −1, i.e. 0.69 kg ha −1 day −1), assessed using 15N pool dilution, were at the lower end of the range previously reported for grasslands. Weekly additions of liquid N fertiliser ([NH 4] 2SO 4, NH 4NO 3 or KNO 3) and, to a lesser extent the addition of water, increased plant growth substantially, demonstrating that the primary constraint to plant growth was low N availability. In plants that had received NO 3−, the activity of the inducible enzyme nitrate reductase in shoots initially increased in proportion to the amount of NO 3− supplied. However, as above-ground herbage accumulated, nitrate reductase activity declined to similar low levels in all treatments, despite the continuance of the constant NO 3− additions. The decline in NR specific activity reflected declining tissue NO 3− concentrations, although total plant NRA may have remained constant during the period of study. The study has shown that plant growth is limited by low N mineralisation rates and indeed the soil is a sink for much added N. Low water availability provides an additional constraint on N mineralisation in this calcareous grassland soil. Any disturbances in the N cycle which increase the availability of mineral N will result in a substantial increase in plant growth within this ecosystem. 相似文献
11.
Nitrogen dioxide (NO 2•) is a key biological oxidant. It can be derived from peroxynitrite via the interaction of nitric oxide with superoxide, from nitrite with peroxidases, or from autoxidation of nitric oxide. In this study, submicromolar concentrations of NO 2• were generated in < 1 μs using pulse radiolysis, and the kinetics of scavenging NO 2• by glutathione, cysteine, or uric acid were monitored by spectrophotometry. The formation of the urate radical was observed directly, while the production of the oxidizing radical obtained on reaction of NO 2• with the thiols (the thiyl radical) was monitored via oxidation of 2,2′-azino-bis-(3-ethylthiazoline-6-sulfonic acid). At pH 7.4, rate constants for reaction of NO 2• with glutathione, cysteine, and urate were estimated as 2 × 10 7, 5 × 10 7, and 2 × 10 7 M −1 s −1, respectively. The variation of these rate constants with pH indicated that thiolate reacted much faster than undissociated thiol. The dissociation of urate also accelerated reaction with NO 2• at pH > 8. The thiyl radical from GSH reacted with urate with a rate constant of 3 × 10 7 M −1 s −1. The implications of these values are: (i) the lifetime of NO 2• in cytosol is < 10 μs; (ii) thiols are the dominant ‘sink’ for NO 2• in cells/tissue, whereas urate is also a major scavenger in plasma; (iii) the diffusion distance of NO 2• is 0.2 μm in the cytoplasm and < 0.8 μm in plasma; (iv) urate protects GSH against depletion on oxidative challenge from NO 2•; and (v) reactions between NO 2• and thiols/urate severely limit the likelihood of reaction of NO 2• with NO• to form N 2O 3 in the cytoplasm. 相似文献
12.
The concentration of nitrite (NO 2−) increases under inflammatory conditions. However, the physiological role of nitrite is so far controversial discussed: it was reported that effects of HOCl (an important inflammation mediator) on phospholipids (PL) may be enhanced but also reduced in the presence of nitrite. In this paper a simple model system was used: unsaturated phosphatidylcholine (PC) vesicles were treated with HOCl in the presence of varying NaNO2 concentrations and the yield of reaction products was determined by MALDI-TOF MS: the extent of chlorohydrin generation was significantly reduced in the presence of NaNO2 because HOCl is consumed by the oxidation of NO2− to NO3−. Similar results were obtained when HOCl was generated by the myeloperoxidase (MPO)/H2O2/Cl− system or the experiments were carried out in the presence of a simple peptide. It is concluded that the transient products of the reaction between HOCl and NO2− do not have a sufficient reactivity to modify PL. 相似文献
13.
1. Difference spectra, at room and liquid N 2 temperatures, of S 2O 42−-, and NO 2−-reduced intact cells and cell-free preparations of Nitrobacter agilis demonstrated the presence of cytochromes of the c- and a-types. Reduction of cytochromes by succinate, and to a limited extent, by NADPH also occurred, provided KCN (0.1 mM) was also present. 2. A particulate, heat-labile nitrite oxidase having an absolute requirement for O2 was prepared from N. agilis cells using sonic oscillation and differential centrifugation. The particles also possessed NADH oxidase, succinoxidase, formate oxidase and traces of NADPH oxidase activity. The stoichiometry of the nitrite oxidase reaction approached the theoretical value of 2 moles of NO2− consumed per mole of O2 consumed. The pH optimum of the nitrite oxidase system shifted to progressively more alkaline values as the NO2− concentration was increased, changing from a pH value of 6.8 at 0.6 mM KNO2 to pH 8.0 at 0.01 M KNO2 with apparent Km's of 0.2 and 1.2 mM NO2−, respectively. Computations of the HNO2 concentrations present under the above conditions showed an approx. 500-fold greater affinity for HNO2 which was independent of pH, suggesting the involvement of HNO2 as both a substrate and an inhibitor (at higher concentrations) of the nitrite oxidase system. The marked inhibition by NaN3, NaCN and Na2S, as well the light-reversible inhibition by CO, indicated the presence of cytochrome oxidase which was subsequently characterized. NO2− proved to be a competitive inhibitor of the nitrite oxidase system. 3. The particulate preparation also possessed a heat-labile nitrite-cytochrome c reductase activity which was energy independent and routinely measured under anaerobic conditions. As in the case of nitrite oxidase, the affinity of the enzyme for NO3− increased as the pH was lowered, but the pH optimum remained unaffected. In terms of calculated HNO2 concentration an approximately constant Km of about 0.2 μM was estimated at the several pH's examined. The inhibition by NO3− was shown to be competitive. The marked sensitivity of the reductase to several metal-binding agents implicated a metal component in the electron transport chain at the site prior to cytochrome c. 4. The membrane-like composition of the nitrite oxidase system is indicated. 相似文献
14.
Mixed microphytobenthos communities, manipulated in two different ways in the laboratory (semi-natural and sediment-stripped), were examined for their response to dissolved free amino acids (DFAA) and nitrate (NO 3−). The semi-natural manipulation involved only the removal of macrofauna; and the sediment-stripped community used microfauna and flora that were separated from natural sediment and re-established on clean sediment, that is, certain indigenous nutrient sources were removed. Using sediment collected on two different occasions, two sets of experiments were made (3 and 4 week), under different light conditions. The response by the communities to the added nitrogen was measured as biomass (Chl a) and primary production. The stimulus from the DFAA addition on microphytobenthos biomass and primary production was similar to or higher than that from NO 3−. A conclusively positive effect from the nitrogen additions could be measured only in the sediment-stripped community. Compared to the semi-natural community, the sediment-stripped community responded faster to the added DFAA. When light was limiting, biomass and production by the sediment-stripped community was enhanced by the N additions, in particular by the DFAA addition. Results suggest that an efficient recycling of nitrogen allows generally nitrogen-poor sandy sediments to sustain high microphytobenthos productivity, thereby retaining nitrogen within the system. 相似文献
15.
In this study, we analysed the nitrifying microbial community (ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB)) within three different aerobic granular sludge treatment systems as well as within one flocculent sludge system. Granular samples were taken from one pilot plant run on municipal wastewater as well as from two lab-scale reactors. Fluorescent in situ hybridization (FISH) and quantitative PCR (qPCR) showed that Nitrobacter was the dominant NOB in acetate-fed aerobic granules. In the conventional system, both Nitrospira and Nitrobacter were present in similar amounts. Remarkably, the NOB/AOB ratio in aerobic granular sludge was elevated but not in the conventional treatment plant suggesting that the growth of Nitrobacter within aerobic granular sludge, in particular, was partly uncoupled from the lithotrophic nitrite supply from AOB. This was supported by activity measurements which showed an approximately threefold higher nitrite oxidizing capacity than ammonium oxidizing capacity. Based on these findings, two hypotheses were considered: either Nitrobacter grew mixotrophically by acetate-dependent dissimilatory nitrate reduction (ping-pong effect) or a nitrite oxidation/nitrate reduction loop (nitrite loop) occurred in which denitrifiers reduced nitrate to nitrite supplying additional nitrite for the NOB apart from the AOB. 相似文献
16.
The effects of external carbon source (both type and concentration) and empty bed contact time (EBCT) on denitrification efficiency during simultaneous heterotrophic and sulfur-utilizing autotrophic denitrification were evaluated. Continuous experiments were conducted with up-flow mode sulfur packed bed reactors (SPBRs) fed with nitrified leachate containing 700–900 mg/l NO 3−–N. The fraction of NO 3−–N removed by heterotrophic denitrification (HDNR fraction) for alkalinity production to balance the alkalinity consumption by autotrophic denitrification varied with the type of external carbon source. When methanol or sodium acetate was added at HDNR fraction values of 60 and 44%, respectively, 100% denitrification was achieved without alkalinity addition. However, glucose required a HDNR fraction value of 70% for complete denitrification and denitrification was not complete when molasses was used at a HDNR fraction value of 70%. The EBCT and volumetric loading rate at which 100% denitrification efficiency could be achieved were 6.76 h and 2.84 kg NO 3−–N/m 3 day, respectively. The maximum nitrogen removal rate was 5.05 kg NO 3−–N/m 3 day observed with 89% removal efficiency. At short HRT, a clogging problem was observed near the bottom of the SPBR with excess growth of heterotrophic denitrifiers and gas accumulation within the pores of the SPBR. This problem may be eliminated by back-washing or by separating heterotrophic denitrification from sulfur-utilizing denitrification. 相似文献
17.
Complete granulation of nitrifying sludge was achieved in a sequencing batch reactor. For the granular sludge, batch experiments
were conducted to characterize the kinetic features of ammonia oxidizers (AOB) and nitrite oxidizers (NOB) in the granules
using the respirometric method. A two-step nitrification model was established to determine the kinetic parameters of both
AOB and NOB. In addition to nitrification reactions, the new model also took into account biomass maintenance and mass transfer
through the granules. The yield coefficient, maximum specific growth rate, and affinity constant for ammonium for AOB were
0.21 g chemical oxygen demand (COD) g −1 N, 0.09 h −1, and 9.1 mg N L −1, respectively, whereas the corresponding values for NOB were 0.05 g COD g −1 N, 0.11 h −1, and 4.85 mg N L −1, respectively. The model developed in this study performed well in simulating the oxygen uptake rate and nitrogen conversion
kinetics and in predicting the oxygen consumption of the AOB and NOB in aerobic granules. 相似文献
18.
Exopolysaccharide production by the marine bacterium Alteromonas sp. strain 1644 was shown to be stimulated by restricted growth conditions and was optimized in nitrogen limited fed-batch cultures. Exopolysaccharides were either partly secreted in the medium or stayed firmly cell-associated. The cell-polysaccharide associations could be destroyed by dialysis against distilled water, allowing polysaccharide purification. The chemical and rheological characterization of this last polysaccharide showed that it was different from the secreted polysaccharide that has been previously described (polysaccharide 1644). At low ionic concentration (below 0.03 M whatever the nature of the ions), solutions of this new polysaccharide had very low viscosities. However, at higher ionic concentration, it formed a gel or exhibited in solution at low polymer concentration an unusually high temperature dependent viscosity. This behaviour was also dependent on the nature of the ions and the following sequences for cations and anions were NH4 + > Mg 2+ > Na + > Li + > K + > TMA + and Br − > NO 3− > SO 42− > Cl − > I − respectively. 相似文献
19.
Single-stage nitritation–anammox combines the growth of aerobic ammonium-oxidizing bacteria (AOB) and anaerobic ammonium oxidizing bacteria (AnAOB) in one reactor. The necessary compromise of their milieu conditions often leads to the growth of nitrite-oxidizing bacteria (NOB). For this study, a sequencing batch reactor (SBR) for nitritation–anammox was operated for 180 days with sewage sludge reject water (removal capacity, 0.4 kg?N?m ?3?day ?1). The growth of NOB was favored by enhanced oxygen supply rather than extended aerobic phases. Suspended-type biomass from this SBR was taken regularly and sieved into three size fractions (all of them <1,000 μm). Batch experiments as well as fluorescence in situ hybridization were performed to study the distribution and activity of AnAOB, AOB, and NOB within those size fractions. Both the measured conversion rates and detected abundances decreased with increasing size fraction. The highest anammox conversion rates (15 g NH 4 +–N per kilogram VSS per hour) and the highest abundances of Brocadia fulgida were found in the medium size fraction (100–315 μm). The batch experiments proved to be accurate tools for the monitoring of multiple processes in the reactor. The results were representative for reactor performance during the 6 months of reactor operation. 相似文献
20.
Nitrification is an important process for nitrogen removal in many wastewater treatment plants, which requires the mutualistic oxidation of ammonia to nitrate by ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). However, this process can be quite unpredictable because both guilds are conditionally sensitive to small changes in operating conditions. Here, dynamics are examined within the NOB guild in two parallel chemostats operated at low and high dilution rates (0.10 and 0.83 day(-1), respectively) during periods of varying nitrification performance. NOB and AOB guild abundances and nitrogen-oxidation efficiency were relatively constant over time in the 0.10 day(-1) reactor; however, the 0.83 day(-1) reactor had two major disturbance episodes that caused destabilization of the NOB guild, which ultimately led to nitrification failure. The first episode caused the extinction of Nitrospira spp. from the system, resulting in chronic incomplete ammonia oxidation and nitrite accumulation. The second episode caused complete loss of nitrification activity, likely resulting from metal toxicity and the previous extinction of Nitrospira spp. from the system. These results exemplify the types of changes that can occur within the NOB guild that result in process impairment or failure, and provide one possible explanation for why nitrification is often unstable at higher dilution rates. 相似文献
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