Maximum Oxidation Rate Research Articles

Inhibitory effects of sulfur compounds on methane oxidation by a methane-oxidizing consortium

Kinetic and enzymatic inhibition experiments were performed to investigate the effects of methanethiol (MT) and hydrogen sulfide (H2S) on methane oxidation by a methane-oxidizing consortium. In the coexistence of MT and H2S, the oxidation of methane was delayed until MT and H2S were completely degraded. MT and H2S could be degraded, both with and without methane. The kinetic analysis revealed that the methane-oxidizing consortium showed a maximum methane oxidation rate (Vmax) of 3.7 mmol g-dry cell weight (DCW)(-1) h(-1) and a saturation constant (Km) of 184.1 μM. MT and H2S show competitive inhibition on methane oxidation, with inhibition values (Ki) of 1504.8 and 359.8 μM, respectively. MT was primary removed by particulate methane monooxygenases (pMMO) of the consortium, while H2S was degraded by the other microorganisms or enzymes in the consortium. DNA and mRNA transcript levels of the pmoA gene expressions were decreased to ∼10(6) and 10(3)pmoA gene copy number g-DCW(-1) after MT and H2S degradation, respectively; however, both the amount of the DNA and mRNA transcript recovered their initial levels of ∼10(7) and 10(5)pmoA gene copy number g-DCW(-1) after methane oxidation, respectively. The gene expression results indicate that the pmoA gene could be rapidly reproducible after methane oxidation. This study provides comprehensive information of kinetic interactions between methane and sulfur compounds.

Preparation and characterization of C/SiO2/SiC aerogels based on novolac/silica hybrid hyperporous materials

Novolac/silica hybrid gels (N/SiO2) are synthesized using the sol–gel polymerization method under a solvent-vapor saturated atmosphere, followed by an ambient-pressure drying technique. Moreover, prepared N/SiO2 aerogels are converted to carbon/silica (C/SiO2) and carbon/silica/silicon carbide (C/SiO2/SiC) nanocomposite aerogels through pyrolysis and carbothermal reduction at 800 and 1500°C, respectively. X-ray diffraction studies reveal the formation of graphite, cristobalite and β-SiC portions in the structure of prepared C/SiO2/SiC aerogels. Mercury porosimetry and scanning electron microscopy results demonstrate that the structural characteristics of fabricated nanocomposite aerogels retained after heat treatment steps. Thermogravimetric analysis and compressive strength measurements are used to investigate thermal and mechanical properties of prepared aerogels, respectively. The maximum oxidation rate temperature increased from 588°C for carbon aerogel to about 750°C for C/SiO2/SiC aerogels. The thermal conductivity coefficient of C/SiO2 and C/SiO2/SiC aerogels at room temperature are about 0.058 and 0.121 (Wm−1K−1), respectively. Compressive strength of C/SiO2/SiC aerogels is in the range of 1.8–2.3MPa. This is very impressive as the compressive strength of novolac/silica aerogels is in the range of 0.2–1.4MPa.

Thermal oxidation and degradation of poly-3-hydroxybutyrate nonwoven materials

Studies of the thermal degradation of poly-3-hydroxybutyrate samples in the presence and absence of oxygen demonstrate that, in the first case, the degradation begins sooner, but the decomposition temperature (maximum of degradation peak) changes only slightly for two different types of samples. It is shown that the activation energy for the thermal degradation of samples without access of oxygen is higher. According to the oxygen uptake curves at T = 150°C and an oxygen pressure of p = 600 Torr, the longest induction period is observed for film samples, whereas the maximum rate of oxidation, for fine nonwoven fiber samples. The kinetics of water uptake is investigated, which shows that the thermophysical characteristics of the samples alter after exposure to an aquatic environment.

Activity and thermal stability of Pt/Ce0.64Mn0.16R0.2Ox (R = Al, Zr, La, or Y) for soot and NO oxidation

In this study, Al2O3, ZrO2, La2O3, and Y2O3 were separately introduced into Pt/CeO2-MnOx catalyst to improve the thermal stability of catalysts and obtain a better soot and NO oxidation activity after thermal treatment. CeO2-MnOx-ROx (R=Al, La, Y, or Zr) mixed oxides were prepared by a co-precipitation method. The catalysts were characterized by XRD, BET, H2-TPR, CO chemisorption, XPS, TG analysis, soot–TPO, and NO–TPO. It is found that the introduction of Rn+ into CeO2-MnOx markedly increases the thermal stability of the catalysts for soot and NO oxidation, remaining a better catalytic oxidation activity. On the one hand, after high-temperature aging, for the modified catalyst Pt/CeMnROx, the ignition temperature of soot oxidation (Ti) and maximal soot oxidation rate temperature (Tm) increase by 30–50°C and 4–32°C, respectively, whereas Al3+-modified catalyst shows the best thermal stability. On the other hand, due to a key role of NO2 as a strong oxidizing agent in soot oxidation process, the NO oxidation activity is often considered as an important aspect. This work shows that Rn+-modified catalysts display a better stability on NO oxidation activity after aging. Some factors leading to the thermal deactivation of catalysts are also discussed in this paper.

Preparation and NOx-assisted soot oxidation activity of a CuO–CeO2 mixed oxide catalyst

A CuO–CeO2 mixed oxide catalyst is synthesized via the urea-nitrate combustion method. The catalytic activity in the reaction of NOx-assisted soot oxidation is evaluated with a TG/DTG technique. The sample Cu1Ce9 possesses the lowest temperature (Tm=383°C) of the maximum soot oxidation rate and the largest specific surface area (65.1m2/g) among the samples examined. The XRD results show that the fluorite-type CeO2 exists in all the samples forming a solid solution with CuO. Crystalline copper oxide phases are not detectable if the Cu/(Cu+Ce) atomic ratio is lower than 0.25. The activity and NOx-TPD results prove that NO2 formed from NO and the nitrate species play crucial roles for soot oxidation in NOx atmosphere. Kinetic parameters, such as the activation energy and reaction order, corresponding to the oxidation of soot are calculated with a differential method.

Severely obese adolescent girls rely earlier on carbohydrates during walking than normal-weight matched girls

The purpose of this study was to determine the substrate oxidation rate and the exercise intensity at which maximal lipid oxidation and ventilatory threshold (VT) occur in obese (BMI: 36.6 ± 6.3 kg · m−2) and normal-weight adolescent girls (BMI: 18.7 ± 1.6 kg · m−2) aged 14–18 years. Substrate oxidation rate was determined by gas exchange using an incremental field test involving walking. Body composition was assessed by bioelectrical impedance. Carbohydrate oxidation rates were significantly higher in obese than in normal-weight girls at speeds ranging from 4 to 6 km · h−1 (P < 0.05), whereas no significant differences were observed between groups regarding lipid oxidation rates. The crossover point of substrate utilisation and the VT were significantly lower in obese than in normal-weight adolescents (P < 0.05). Maximal lipid oxidation rate was observed at 46 ± 15 and 53 ± 15 %EO2max in obese and normal-weight adolescents, respectively. At these intensities, the Lipoxmax was significantly lower in obese than in normal-weight girls (6.7 ± 2.3 versus 8.9 ± 3.5 mg · min−1 · kg−1 FFM, P < 0.05, 95% CI: −3.7 to −0.7, d = −0.74). The present results have implications in designing interventions to promote lipid oxidation and energy expenditure during walking in severely obese adolescent girls.

Influence of pH and pH adjustment conditions on photocatalytic oxidation of aqueous ammonia under airflow over Pt-loaded TiO2

The influence of pH and pH adjustment conditions on the photocatalytic oxidation of aqueous ammonia in the presence of Pt-TiO2 under airflow was investigated as a possible treatment for ammonia-containing wastewater. Ammonia oxidation proceeded only under alkaline conditions, and the maximum initial oxidation rate was obtained at pH∼10. The pH of the reaction suspension decreased with the formation of nitrite and nitrate species, stopping completely when the pH fell below 7 for reactions in which the initial pH (pHi) was adjusted within the range 8.7–11.3 using NaOH(aq). The rate of ammonia oxidation was higher when NaOH(aq) was used to adjust the pHi than that achieved using Na2CO3–NaHCO3 buffer solution at the same pH. The maximum ammonia adsorption on Pt-TiO2 (measured under dark conditions) was obtained at pH 10 and the amount of ammonia adsorbed when the pHi was adjusted with NaOH(aq) was higher than that achieved using the Na2CO3–NaHCO3 buffer solution at the same pH; thus, the amount of adsorbed ammonia strongly affected the oxidation rate. Although the selectivity for the sum of the undesired products, nitrite and nitrate was high when the ammonia concentration was low (e.g., 5mM), the selectivity decreased as the initial ammonia concentration increased for each pH and pH adjustment condition. Suppression of the selectivity was evident when the pHi was adjusted to 10 with NaOH(aq). The selectivity was affected by the changes in the density of N-containing species on the photocatalyst surface as the pH and pH adjustment conditions were varied.

Impact of oxygen transport properties on polypropylene thermal oxidation, part 1: Effect of oxygen solubility

ABSTRACTA general kinetic model is proposed to describe the polypropylene thermal oxidation of thin polypropylene films in a wide range of temperatures (from 60 to 200°C) and oxygen partial pressures (from 0.02 to 5 MPa) using a single set of parameters. This model was calibrated with several series of experimental data including analyses of primary (hydroperoxides) and secondary oxidation products (carbonyl species), and subsequent changes in macromolecular properties (average molecular masses). It predicts the experimental data previously published in the literature in terms of induction times and maximal oxidation rates. The variability of the oxygen solubility coefficient allows to explain the scattering of induction times and oxidation rates among the whole iPP family, but also the dependence of this latter quantity with oxygen partial pressure. This variability is presumably due to iPP polymorphism in the temperature range where oxygen permeability is commonly measured. It is concluded that the kinetic model can be used to study the direct effect of iPP morphology on its thermal oxidation kinetics (chemistry of oxidation). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41441.

Effects of yttrium ion on formation mechanism of ZrO2-Y2O3 ceramic coatings formed by plasma electrolytic oxidation on Al-12Si alloy

ZrO2-Y2O3 ceramic coating was produced by plasma electrolytic oxidation (PEO) on ZAlSil2Cu3Ni2 alloy. The microstructure and phase composition of the coating were investigated by SEM and XRD. The results show that adding an appropriate amount of yttrium ion can improve the growing rate of ceramic coating at different oxidation stages and decrease arc voltage. The thickness of ZrO2-Y2O3 coating is 16 μm thicker than that of ZrO2 coating and the maximum oxidation rate improves by 0.6 μm/min. In addition, the arc voltage decreases from 227 to 172 V. It can be seen that the rate of oxidation firstly increases to some extent and then decreases with the content of yttrium ion increasing. The growth rate reaches the maximum while the content of yttrium ion is 0.05 g·L−1. The maximum thickness is 90 μm.Compared to ZrO2 coating, the micropores of ZrO2-Y2O3 coating are less and the ceramic layer is repeatedly deposited by ZrO2 and Y2O3 ceramic particles. Meanwhile, the binding force between coating and substrate is better and the coating is uniform and compact. The ceramic layer is mainly composed of c-Y0.15Zr0.85O1.93□0.07, m-ZrO2, α-Al2O3, γ-Al2O3 and Y2O3. It is indicated that ZrO2 has been fully stabilized by yttrium ion through the formation of solid solution.

Structure and catalytic property of CeO2-ZrO2-Fe2O3 mixed oxide catalysts for diesel soot combustion: Effect of preparation method

A series of Ce0.5Fe0.30Zr0.20O2 catalysts were prepared by different methods (co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrothermal method) and characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) and H2-TPR measurements. Potential of the catalysts in the soot oxidation was evaluated in a temperature-programmed oxidation (TPO) apparatus. The results showed that all the Fe3+ and Zr4+ were incorporated into ceria lattice to form a pure Ce-Fe-Zr-O solid solution for the co-precipitation sample, but two kinds of Fe phases existed in the Ce-Fe-Zr-O catalysts prepared by other methods: Fe3+ incorporated into CeO2 lattice and dispersed Fe2O3 clusters. The free Fe2O3 clusters could improve the activity of catalysts for soot oxidation comparing with the pure Ce-Fe-Zr-O solid solution owing to the synergetic effect between free Fe2O3 and surface oxygen vacancies. In addition, the activity of catalysts strongly relied on the surface reducibility of free Fe2O3 particles. Holding both abundant free Fe2O3 particles and high oxygen vacancy concentration, the hydrothermal Ce0.5Fe0.3Zr0.2O2 catalyst presented the lowest Ti (251 °C, ignition temperature of soot oxidation) and Tm (310 °C, maximum oxidation rate temperature) for soot combustion (with tight-contact between soot and catalysts) among the five samples. Even after aging at 800 °C for 10 h, the Ti and Tm were still relatively low, at 273 and 361 °C, respectively, indicating high catalytic stability.

Non-Isothermal Method for Charactering the Oxidation Resistance Property of SiAlON Materials

The oxidation resistance of SiAlONs is one important property. In our work we present a test method to characterize its anti-oxidation property with the non-isothermal oxidation process using Thermo Gravimetric Analyzer (TGA). The oxidation starting temperature (Ts), maximum oxidation rate temperature (Tm) and the value of the oxidation weight gain per unit area (Ga) are three key parameters to describe the antioxidant properties of the material. Experimental results prove this test method is easy and reasonable and it will be developed as the national standard of China.

The Gibbs Free Energy Threshold for the Invasion of a Microbial Population Under Kinetic Constraints

Possible chemotrophic metabolism at a site of interest is controlled not only by the catabolic energy expressed as the Gibbs energy of reaction (ΔrG) but also by the kinetic constraints due to the availability of electron acceptors and donors. We introduced graphical and stochastic approaches for determining the ΔrG threshold required to support a microbial population with a specific catabolic strategy under kinetic constraints. Invasibility as an indicator of the present reproductive ability of a microbial population was evaluated by simultaneously calculating ΔrG for the catabolic reaction and the microbial catalytic rate. For example, the neutrophilic iron-oxidizing bacteria's invasibility was calculated by randomly choosing the Fe2+ and O2 concentrations between 10−8 and 10−2 mol L−1, and pH between 4 and 8, to determine the ΔrG threshold for invasion. Parameters were estimated from batch experiments of neutrophilic iron-oxidizing bacteria reported in previous studies. Under the given conditions, the stochastic approach predicted that the neutrophilic iron-oxidizing bacteria can always invade a system in which the ΔrG for Fe oxidation is below −90 kJ mol Fe−1, can occasionally invade if ΔrG is between −45 and −90 kJ mol Fe−1, and can never invade if ΔrG is above −45 kJ mol Fe−1. The ΔrG threshold for invasion is sifted by the growth yield coefficient, the loss rate of cells, the maximum cell-specific Fe oxidation rate constant, and the temperature. The ΔrG threshold for invasion may be unable to rigorously predict the stable dominance of microbial metabolism, but can provide a rough indication for the possible microbial metabolism under current conditions.

Ceria Prepared by Flame Spray Pyrolysis as an Efficient Catalyst for Oxidation of Diesel Soot

Ceria has been prepared by flame spray pyrolysis and tested for activity in catalytic soot oxidation. In tight contact with soot the oxidation activity (measured in terms of the temperature of maximal oxidation rate, Tmax) of the flame made ceria is among the highest reported for CeO2. This can to a significant degree be ascribed to the large surface area achieved with the flame spray pyrolysis method. The importance of the inherent soot reactivity for the catalytic oxidation was studied using various soot samples, and the reactivity of the soot was found to have a significant impact, as the Tmax-value for oxidation in tight contact with a catalyst scaled linearly with the Tmax-value in non-catalytic soot oxidation. The Tmax-value in non-catalytic soot oxidation was in turn observed to scale linearly with the H/C ratio of the carbonaceous materials.

De novo synthesis of brominated dioxins and furans.

On the basis of laboratory experiments with model mixtures (active carbon+CuBr2 at different loads), this work studies the formation of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) by de novo synthesis. For the different samples, the temperature of the maximum carbon oxidation rate was determined by thermogravimetric analysis, and a kinetic model was proposed for the degradation of the materials in an oxidizing atmosphere (synthetic air). The effect of the addition of different amounts of CuBr2 was studied, finding that its presence accelerates the degradation of the carbonaceous structure in the presence of oxygen. The thermal degradation of the samples in air is satisfactorily described by a first-order single-reaction model. In addition, combustion runs of one of the mixtures (consisting of activated carbon+50 wt % CuBr2, pyrolyzed at 700 °C) were performed in a quartz horizontal laboratory furnace. The analysis of the emissions and the solid residue proved the formation of brominated dioxins and furans at 300, 400, and 500 °C, with a maximum yield at 300 °C (91.7 ng/g of total PBDD/Fs) and a higher bromination degree with increasing temperature.

Enhanced soot combustion over partially substituted hydrotalcite-drived mixed oxide catalysts CoMgAlLaO

A series of hydrotalcite-derived multicomponent oxide catalysts Co2.5Mg0.5Al1–x%Lax%O (denoted as CMALax, x=0, 5, 8, 10 or 15) with different La contents were synthesized by co-precipitation, and employed for catalytic soot combustion and NOx storage at lean condition. It is found that the La-substituted catalysts are more active than the one without La for soot combustion and NOx storage. Among all the catalysts CMALax, CMALa10 (x=10) exhibits the highest catalytic performance, showing the largest NOx storage capacity (300μmol/g) and the lowest temperature for the maximal soot oxidation rate (Tm=388°C). The results of H2-TPR and O2-TPD indicate that the La-substitution can enhance the redox properties and increase the amount of surface lattice oxygen species of the catalysts. The results of soot combustion kinetics show that the apparent activation energy of CMALa10 is the lowest (92.75kJ/mol). Based upon the catalytic performance and in situ DRIFTS characterization, a nitrate and/or NO2 enhanced soot combustion mechanism over CMALa10 was proposed. It is revealed that at low temperature the stored nitrate can directly promote soot ignition, while at high temperature the NO2 species arising from NO oxidation or nitrate decomposition act as the main active species for soot combustion.

Effects of glycemic control on glucose utilization and mitochondrial respiration during resuscitated murine septic shock.

BackgroundThis study aims to test the hypothesis whether lowering glycemia improves mitochondrial function and thereby attenuates apoptotic cell death during resuscitated murine septic shock.MethodsImmediately and 6 h after cecal ligation and puncture (CLP), mice randomly received either vehicle or the anti-diabetic drug EMD008 (100 μg · g-1). At 15 h post CLP, mice were anesthetized, mechanically ventilated, instrumented and rendered normo- or hyperglycemic (target glycemia 100 ± 20 and 180 ± 50 mg · dL-1, respectively) by infusing stable, non-radioactive isotope-labeled 13C6-glucose. Target hemodynamics was achieved by colloid fluid resuscitation and continuous i.v. noradrenaline, and mechanical ventilation was titrated according to blood gases and pulmonary compliance measurements. Gluconeogenesis and glucose oxidation were derived from blood and expiratory glucose and 13CO2 isotope enrichments, respectively; mathematical modeling allowed analyzing isotope data for glucose uptake as a function of glycemia. Postmortem liver tissue was analyzed for HO-1, AMPK, caspase-3, and Bax (western blotting) expression as well as for mitochondrial respiratory activity (high-resolution respirometry).ResultsHyperglycemia lowered mitochondrial respiratory capacity; EMD008 treatment was associated with increased mitochondrial respiration. Hyperglycemia decreased AMPK phosphorylation, and EMD008 attenuated both this effect as well as the expression of activated caspase-3 and Bax. During hyperglycemia EMD008 increased HO-1 expression. During hyperglycemia, maximal mitochondrial oxidative phosphorylation rate was directly related to HO-1 expression, while it was unrelated to AMPK activation. According to the mathematical modeling, EMD008 increased the slope of glucose uptake plotted as a function of glycemia.ConclusionsDuring resuscitated, polymicrobial, murine septic shock, glycemic control either by reducing glucose infusion rates or EMD008 improved glucose uptake and thereby liver tissue mitochondrial respiratory activity. EMD008 effects were more pronounced during hyperglycemia and coincided with attenuated markers of apoptosis. The effects of glucose control were at least in part due to the up-regulation of HO-1 and activation of AMPK.Electronic supplementary materialThe online version of this article (doi:10.1186/2197-425X-2-19) contains supplementary material, which is available to authorized users.

Anodic ammonia oxidation to nitrogen gas catalyzed by mixed biofilms in bioelectrochemical systems

In this paper we report ammonia oxidation to nitrogen gas using microbes as biocatalyst on the anode, with polarized electrode (+600mV vs. Ag/AgCl) as electron acceptor. In batch experiments, the maximal rate of ammonia-N oxidation by the mixed culture was ∼ 60mgL−1 d−1, and nitrogen gas was the main products in anode compartment. Cyclic voltammetry for testing the electroactivity of the anodic biofilms revealed that an oxidation peak appeared at +600mV (vs. Ag/AgCl), whereas the electrode without biofilms didn’t appear oxidation peak, indicating that the bioanode had good electroactivities for ammonia oxidation. Microbial community analysis of 16S rRNA genes based on high throughput sequencing indicated that the combination of the dominant genera of Nitrosomonas, Comamonas and Paracocus could be important for the electron transfer from ammonia oxidation to anode.

New insights into the influence of activated carbon surface oxygen groups on H2O2 decomposition and oxidation of pre-adsorbed volatile organic compounds

In this study, the influence of the surface oxygen groups of activated carbons (ACs) on the decomposition of H2O2 and the consequent OH radicals generation is investigated. The oxidation of pre-adsorbed volatile organic compounds by H2O2 is also studied. Four ACs, with low percentage of inorganic matter (<0.2%), similar textural properties but differing in their surface oxygen content were evaluated. The surface oxygen groups of the ACs were characterised by using appropriate characterisation techniques (temperature programmed desorption and X-ray photoelectron spectroscopy). The kinetic curves of H2O2 decomposition were very similar for all the ACs. However, different profiles in the production of OH radicals were observed. OH radicals generation seemed to be promoted by low surface oxygen contents. Oxidation of two volatile organic compounds (VOCs) of different polarity, methyl ethyl ketone (MEK) and toluene, pre-adsorbed onto the ACs was finally investigated. H2O2 was used as oxidising agent. Both VOCs presented similar maximum oxidation rates, around 70%, in spite of their different hydrophobicity. Some evidences are provided supporting that oxidation of pre-adsorbed VOCs can take place in the inner pore structure of the ACs.

Effects of adipose tissue distribution on maximum lipid oxidation rate during exercise in normal-weight women

AimFat mass localization affects lipid metabolism differently at rest and during exercise in overweight and normal-weight subjects. The aim of this study was to investigate the impact of a low vs high ratio of abdominal to lower-body fat mass (index of adipose tissue distribution) on the exercise intensity (Lipoxmax) that elicits the maximum lipid oxidation rate in normal-weight women. MethodsTwenty-one normal-weight women (22.0±0.6 years, 22.3±0.1kg.m−2) were separated into two groups of either a low or high abdominal to lower-body fat mass ratio [L-A/LB (n=11) or H-A/LB (n=10), respectively]. Lipoxmax and maximum lipid oxidation rate (MLOR) were determined during a submaximum incremental exercise test. Abdominal and lower-body fat mass were determined from DXA scans. ResultsThe two groups did not differ in aerobic fitness, total fat mass, or total and localized fat-free mass. Lipoxmax and MLOR were significantly lower in H-A/LB vs L-A/LB women (43±3% VO2maxvs 54±4% VO2max, and 4.8±0.6mgmin−1kg FFM−1vs 8.4±0.9mgmin−1kg FFM−1, respectively; P<0.001). Total and abdominal fat mass measurements were negatively associated with Lipoxmax (r=–0.57 and r=–0.64, respectively; P<0.01) and MLOR [r=–0.63 (P<0.01) and r=–0.76 (P<0.001), respectively]. ConclusionThese findings indicate that, in normal-weight women, a predominantly abdominal fat mass distribution compared with a predominantly peripheral fat mass distribution is associated with a lower capacity to maximize lipid oxidation during exercise, as evidenced by their lower Lipoxmax and MLOR.

Reactor performance and microbial ecology of a nitritation membrane bioreactor

Partial nitritation is an indispensable pretreatment for anaerobic ammonium oxidation process. However, the nitritation is limited by the low growth rates of ammonia-oxidizing bacteria (AOB). In this study, a membrane bioreactor (MBR) was operated for 300 days to assess its nitritation performance and the shift of microbial community. Results showed that the reactor obtained satisfying nitritation after a startup period of 50 days, which finally achieved ammonium conversation rates of about 0.8kgN/m3/d. The apparent half-saturation constant (Km) and maximum ammonium oxidation rate (rmax) of the AOB-enriched culture were determined to be 6.1mgN/L and 1.1kgN/g-VSS/d, respectively. In addition, lower fouling rates were found in the initial operating days that the reactor was fed with lower ammonium loads (day 0–day 150). However, the increased ammonium loads (>0.6kgN/m3/d) in the following 150 days resulted in increases in extracellular polysaccharides, leading to much higher fouling rates. 16S rRNA high-throughput sequencing analysis showed clear changes in the microbial community populations during the MBR operation. Results also showed that ordinary heterotrophic organisms and nitrite-oxidizing bacteria were successively inhibited; finally Nitrosomonas dominated in the nitritation MBR, with relative abundance of 40–46%. Moreover, the AOB-enriched culture was of higher microbial diversity than the seeding sludge. This study could not only improve our understanding of the bacterial community dynamics in nitritation processes, but also provide more alternatives for MBR applications.