Optimal operational factors for nitrite accumulation in batch reactors

The environmental factors that affected the accumulation of nitrite in nitrifying reactors were investigated using a mixed culture. A batch reactor with 50 mg-N/l of ammonia was used. The pH, temperature and dissolved oxygen concentration were varied. The concentration of unionized free ammonia also changed with the oxidation of ammonia and the variation of pH and temperature. The accumulation of nitrite was affected sensitively by pH and temperature. A higher nitrite concentration was observed at pH 8-9 or temperature around 30 °C. The dissolved oxygen also affected, giving the highest nitrite accumulation at around 1.5 mg/l. These were the favoredconditions for nitrite production. The free ammonia concentration influenced thenitrite accumulation also, by inhibiting nitrite oxidation. The inhibition becameapparent at a concentration of approximately 4 mg/l or above, but insignificant atbelow 1 mg/l. Thus, simultaneously high free ammonia concentration and maximumspecific ammonia-oxidation rate (above 15 × 10^-3 mg-N/mg-VSSh)were needed for a significant nitrite accumulation. When the two conditions were met, thenthe highest accumulation was observed when the ratio of the maximum specific oxidationrate of ammonia to the maximum specific oxidation rate of nitrite (k_a/k_n) was highest.Under the optimal operating conditions of pH 8, 30 °C and 1.5 mg/l of dissolvedoxygen, as much as 77% of the removed ammonia accumulated in nitrite.     

Determination of the decay rate of nitrifying bacteria

The growth and decay of nitrifying organisms determines the amount of nitrifying bacteria in activated sludge systems. The growth rate of the nitrifying organisms is reasonable, well defined, and studied, while the decay rate is still rather uncertain. Experiments in previous studies were over periods up to 14 days and obtained results were not confirmed. Contradicting decay rates of nitrifiers in different bacterial communities is reported. No differentiation between ammonia and nitrite oxidizers was made. Therefore, in this studyper day the decay rate of the nitrifying organisms was studied. The starvation condition (aerobic, anoxic, or anaerobic), temperature, type of bacterial community, and the presence of higher organisms are the main aspects that were investigated. A simple and reliable method (adapted from previous studies) for determining the decay rate of nitrifying organisms under different starvation conditions and different temperatures was developed. The test procedure has been used for determining the decay rate of ammonium and nitrite oxidizing bacteria in an enriched nitrifying culture and in activated sludge. The test was successfully applied at starvation periods up to 30 days. The decay rate of the enriched culture of nitrifiers was very low compared to values for nitrifiers in activated sludge. The decay rate of the nitrifiers in activated sludge was found to be to 0.2, 0.1, and 0.06 per day for aerobic, anoxic, and anaerobic conditions, respectively. The decay rate of ammonia oxidizers and nitrite oxidizers was the same at the corresponding conditions.     

The effect of hydroxylamine on the activity and aggregate structure of autotrophic nitrifying bioreactor cultures

Addition of hydroxylamine (NH2OH) to autotrophic biomass in nitrifying bioreactors affected the activity, physical structure, and microbial ecology of nitrifying aggregates. When NH2OH is added to nitrifying cultures in 6-h batch experiments, the initial NH3-N uptake rates were physiologically accelerated by a factor of 1.4-13. NH2OH addition caused a 20-40% decrease in the median aggregate size, broadened the shape of the aggregate size distribution by up to 230%, and caused some of the microcolonies to appear slightly more dispersed. Longer term NH2OH addition in fed batch bioreactors decreased the median aggregate size, broadened the aggregate size distribution, and decreased NH3-N removal from >90% to values ranging between 75% and 17%. This altered performance is explained by quantitative fluorescence in situ hybridization (FISH) results that show inhibition of nitrifying populations, and by qPCR results showing that the copy numbers of amoA and nxrA genes gradually decreased by up to an order-of-magnitude. Longer term NH2OH addition damaged the active biomass. This research clarifies the effect of NH2OH on nitrification and demonstrates the need to incorporate NH2OH-related dynamics of the nitrifying biomass into mathematical models, accounting for both ecophysiological and structural responses.     

Origin,causes and effects of increased nitrite concentrations in aquatic environments

Literature frequently mentions increasednitrite concentrations along with itsinhibitory effect towards bacteria and aquaticlife. Nitrite accumulation has been studied fordecades, and although numerous causal factorshave already been commented on in literature,the mechanism of nitrite accumulation is notalways clear. From the broad range ofparameters and environmental factors reviewedin this paper, it is obvious that the causesand consequences of nitrite accumulation arenot yet completely understood. Among others,pH, dissolved oxygen, volatile fatty acids,phosphate and reactor operation have been foundto play a role in nitrite accumulation, whichresults from differential inhibition ordisruption of the linkage of the differentsteps in both nitrification anddenitrification. In the case of nitrification, thisdifferential inhibition could lead to thedisplacement or unlinking of the ammoniaoxidisers and nitrite oxidisers. In this paper,the idea is formulated that the nitrifierpopulation forms a role model for the totalmicrobial community. Increased nitriteconcentrations would in this aspect not onlysignal a disruption of nitrifiers, but possiblyalso of the total configuration of themicrobial community.     

利用烟道气培养产烃葡萄藻的可行性研究

对烟道气培养产烃葡萄藻的可行性进行了研究,重点考察了SO2和NOx的水溶形态对葡萄藻的影响。结果表明,亚硫酸氢盐浓度低于0．8mmol／L时,对葡萄藻生长没有明显抑制作用,可以提供葡萄藻生长的硫源,但高浓度(大于2mmol／L)时抑制细胞生长;当亚硝酸盐浓度小于8mmol／L时,可以作为葡萄藻生长的唯一氮源,亚硝酸盐的去除主要是由微藻利用所致。当起始浓度为2mmol／L和4mmol／L时,亚硝酸盐的去除率分别为100％和99．7％。     

Concurrent nitrite oxidation and aerobic denitrification in activated sludge exposed to volatile fatty acids

The goal of this research was to investigate the simultaneous occurrence of nitrification and denitrification by activated sludge exposed to volatile fatty acids (VFAs) during aerobic wastewater treatment using a single-stage reactor. A mixture of VFAs was spiked directly into a continuous-stirred tank reactor (CSTR) to assess subsequent impacts on nitrite removal, nitrate formation, CO(2) fixation, total bacterial density, and dominant nitrite oxidizing bacteria (NOB) concentration (i.e., Nitrospira). The activity of the periplasmic nitrate reductase (NAP) enzyme and the presence of nap gene were also measured. A rapid decrease in the nitrate formation rate (>70% reduction) was measured for activated sludge exposed to VFAs; however, the nitrite removal rate was not reduced. The total bacterial density and Nitrospira concentration remained essentially constant; therefore, the reduction in nitrate formation rate was likely not due to heterotrophic uptake of nitrogen or to a decrease in the dominant NOB population. Additionally, VFA exposure did not impact microbial CO(2) fixation efficiency. The activity of NAP enzyme increased in the presence of VFAs suggesting that nitrate produced as a consequence of nitrite oxidation was likely further reduced to gaseous denitrification products via catalysis by NAP. Little, if any, nitrogen was discharged in the aqueous effluent of the CSTR after exposure to VFAs demonstrating that activated sludge treatment yielded compounds other than those typically produced solely by nitrification.     

Effects of temperature on simultaneous nitrification and denitrification via nitrite in a sequencing batch biofilm reactor

A laboratory scale experiment was described in this paper to enhance biological nitrogen removal by simultaneous nitrification and denitrification (SND) via nitrite with a sequencing batch biofilm reactor (SBBR). Under conditions of total nitrogen (TN) about 30 mg/L and pH ranged 7.15–7.62, synthetic wastewater was cyclically operated within the reactor for 110 days. Optimal operation conditions were established to obtain consistently high TN removal rate and nitrite accumulation ratio, which included an optimal temperature of 31 °C and an aeration time of 5 h under the air flow of 50 L/h. Stable nitrite accumulation could be realized under different temperatures and the nitrite accumulation ratio increased with an increase of temperature from 15 to 35 °C. The highest TN removal rate (91.9%) was at 31 °C with DO ranged 3–4 mg/L. Process control could be achieved by observing changes in DO and pH to judge the end-point of oxidation of ammonia and SND.     

Enhanced nitrite build-up in proportion to increasing alklinity/NH4+ ratio of influent in biofilm reactor

When the alkalinity/NH₄ ⁺ratio increased from 4.1 to 9.4, the ammonium removal rate increased from 45 to 90 mg NO_x-N l^–1 h^–1. An increase in alkalinity/NH₄ ⁺ratio was a major reason for higher pH and free ammonia (FA) concentration in the reactor. The high concentration of FA showed a selective inhibition for Nitrobacter, which caused enhanced nitrite build-up in a biofilm reactor.     

Enzymology of the oxidation of ammonia to nitrite by bacteria

The enzymes which catalyze the oxidation of ammonia to nitrite by autotrophic bacteria are reviewed. A comparison is made with enzymes which catalyze the same reactions in methylotrophs and organotrophic heterotrophic bacteria.     

美味牛肝菌降低泡菜中亚硝酸盐含量的研究

亚硝酸盐是泡菜发酵过程中产生的一种有害的副产物。首次发现美味牛肝菌Boletus edulis子实体能显著降低泡菜中亚硝酸盐的含量。在实验组原料中加入新鲜美味牛肝菌子实体时,发酵第4天亚硝酸盐含量可降低97.1%。当泡菜中冷冻保藏的美味牛肝菌子实体的加入量分别为10%、20%、30%、40% 和50%时,发酵第4天对应的亚硝酸盐含量比不加美味牛肝菌的对照分别降低了20.9%、51.6%、93.9%、96.1% 和96.9%。发酵第6天开始亚硝酸盐含量降低百分比逐渐减小,发酵10d以上实验组和对照组中亚硝酸盐含量趋于一致,但此时的泡菜酸度增加、质量降低。此外,新鲜的和冷冻的美味牛肝菌子实体降低泡菜中亚硝酸盐的活性最高,常温晾干的活性次之,高温烘干的美味牛肝菌子实体没有降低亚硝酸盐的活性。     

Effect of pH and nitrite concentration on nitrite oxidation rate

The effect of pH and nitrite concentration on the activity of the nitrite oxidizing bacteria (NOB) in an activated sludge reactor has been determined by means of laboratory batch experiments based on respirometric techniques. The bacterial activity was measured at different pH and at different total nitrite concentrations (TNO?). The experimental results showed that the nitrite oxidation rate (NOR) depends on the TNO? concentration independently of the free nitrous acid (FNA) concentration, so FNA cannot be considered as the real substrate for NOB. NOB were strongly affected by low pH values (no activity was detected at pH 6.5) but no inhibition was observed at high pH values (activity was nearly the same for the pH range 7.5-9.95). A kinetic expression for nitrite oxidation process including switch functions to model the effect of TNO? concentration and pH inhibition is proposed. Substrate half saturation constant and pH inhibition constants have been obtained.     

Distinctive microbial ecology and biokinetics of autotrophic ammonia and nitrite oxidation in a partial nitrification bioreactor

Biological nitrogen removal (BNR) based on partial nitrification and denitrification via nitrite is a cost-effective alternate to conventional nitrification and denitrification (via nitrate). The goal of this study was to investigate the microbial ecology, biokinetics, and stability of partial nitrification. Stable long-term partial nitrification resulting in 82.1 +/- 17.2% ammonia oxidation, primarily to nitrite (77.3 +/- 19.5% of the ammonia oxidized) was achieved in a lab-scale bioreactor by operation at a pH, dissolved oxygen and solids retention time of 7.5 +/- 0.1, 1.54 +/- 0.87 mg O(2)/L, and 3.0 days, respectively. Bioreactor ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) populations were most closely related to Nitrosomonas europaea and Nitrobacter spp., respectively. The AOB population fraction varied in the range 61 +/- 45% and was much higher than the NOB fraction, 0.71 +/- 1.1%. Using direct measures of bacterial concentrations in conjunction with independent activity measures and mass balances, the maximum specific growth rate (micro(max)), specific decay (b) and observed biomass yield coefficients (Y(obs)) for AOB were 1.08 +/- 1.03 day(-1), 0.32 +/- 0.34 day(-1), and 0.15 +/- 0.06 mg biomass COD/mg N oxidized, respectively. Corresponding micro(max), b, and Y(obs) values for NOB were 2.6 +/- 2.05 day(-1), 1.7 +/- 1.9 day(-1), and 0.04 +/- 0.02 mg biomass COD/mg N oxidized, respectively. The results of this study demonstrate that the highly selective partial nitrification operating conditions enriched for a narrow diversity of rapidly growing AOB and NOB populations unlike conventional BNR reactors, which host a broader diversity of nitrifying bacteria. Further, direct measures of microbial abundance enabled not only elucidation of mixed community microbial ecology but also estimation of key engineering parameters describing bioreactor systems supporting these communities.     

An iron dioxygenase from Alcaligenes faecalis catalyzing the oxidation of pyruvic oxime to nitrite

Abstract An enzyme which participated in the oxidation of hydroxylamine to nitrite from was partially purified Alcaligenes faecalis , and some of its properties were studied. The enzyme oxidized aerobically pyruvic oxime to nitrite in the presence of hydroxylamine or ascorbate. As molecular oxygen equimolar to nitrite formed was consumed in the enzymatic oxidation of pyruvic oxime to nitrite, the enzyme was thought to be a dioxygenase. It was an iron protein, and a reducing reagent was required to keep the iron in the ferrous state for the action of the enzyme.     

Effect of acute and chronic ammonia and nitrite exposure on oxygen consumption and growth of juvenile big bellied seahorse

Juvenile big bellied seahorse Hippocampus abdominalis were exposed acutely and chronically to elevated ammonia and nitrite {24 h exposure: 0·01, 5·0, 10·1, 14·8 and 19·9 mg l⁻¹ total ammonia-nitrogen [TA-N] and <0·001, 74·4, 99·2 and 123·6 mg l⁻¹ [NO₂-N] nitrite-nitrogen and 35 days exposure: 0·11, 0·55, 1·67 and 3·07 mg l⁻¹ TAN and <0·001, 0·92, 4·67 and 9·10 mg NO₂-N l⁻¹}. Significant ( P <0·001) increases in oxygen consumption rate and ventilation frequency occurred at 14·8, 19·9 mg l⁻¹ TA-N and 99·2, 123·6 mg l⁻¹ NO₂-N for acutely exposed fish. Oxygen consumption rate was significantly ( P <0·05) elevated at 1·67 and 3·07 mg l⁻¹ TA-N in chronically treated fish and ventilation frequency increased significantly ( P <0·05) at 0·55, 1·67, 3·07 mg l⁻¹ TA-N and 4·59, 9·10 mg l⁻¹ NO₂-N. There were no significant differences in growth between controls and ammonia exposed fish. Mortalities occurred at 14·8, 19·9 mg l⁻¹ TA-N.     

Effect of acute sodium nitrite intoxication on some essential biometals in mouse spleen

Background and aimSodium nitrite (NaNO₂) is an inorganic salt with numerous applications in a variety of industries, as well as in medicine. Nevertheless, exposure to high levels of NaNO₂ is toxic for animals and humans. Sodium nitrite intoxication is shown to decrease the activity of major antioxidant defence enzymes which is dependent on the maintenance of specific ion equilibrium. The aim of the present study was to investigate the effect of acute NaNO₂ intoxication on the content of the essential metals iron (Fe), calcium (Ca) and zinc (Zn) in mouse spleen.MethodsMature male ICR mice were divided into four groups and subjected to acute NaNO₂ exposure by a single intraperitoneal injection of 120 mg/kg body weight. Animals in each group were sacrificed at certain time interval after treatment (1 h, 5 h, 1 day and 2 days). Spleens were excised and processed for atomic absorption spectrometry analysis of Fe, Ca and Zn content.ResultsAt the first hour after treatment, a decrease in Fe and Ca levels was observed. One day following NaNO₂ administration, Zn concentration reached its lowest value and Ca levels remained lower, compared to the untreated controls. In contrast, Fe concentration increased on the first and second day after treatment.ConclusionThe results of the present study demonstrate that acute NaNO₂ intoxication provokes changes in the endogenous levels of Fe, Ca and Zn in mouse spleen. These findings suggest disruption of the ionic balance and impact on the activity of antioxidant defence enzymes.     

A thermoluminescence study of the effects of nitrite on photosystem II in spinach thylakoids.

The site of action of nitrite on PS II was investigated by measuring the TL profile of nitrite-treated spinach thylakoid membranes. Three bands were observed in control, which were identified as the Q band (7 degrees C), the B band (24 degrees C) and the C band (57 degrees C). In the presence of 20 mmol/L nitrite, the intensity of the Q band decreased, the B band upshifted to 46 degrees C but the C band disappeared. The suppression of the Q band and the upshift of the B band suggested that nitrite caused inhibition at the water oxidizing complex. The effects of nitrite also remained the same in the presence of chloride. In case of ion-sufficient thylakoid membranes, nitrite decreased the Q band peak intensity and caused an upshift in the B band peak temperature. Nitrite showed similar effects in the presence of DCMU. This suggested that the site of action of nitrite is not at the acceptor side but at the donor side of PS II. The inhibition shown by nitrite has been found to be specific for nitrite anion. No other anions such as formate, fluoride or nitrate, were effective.     

Development and application of a PCR-denaturing gradient gel electrophoresis tool to study the diversity of Nitrobacter-like nxrA sequences in soil

A new PCR-denaturing gel gradient electrophoresis (DGGE) tool based on the functional gene nxrA encoding the catalytic subunit of the nitrite oxidoreductase in nitrite-oxidizing bacteria (NOB) has been developed. The first aim was to determine if the primers could target representatives of NOB genera: Nitrococcus and Nitrospira. The primers successfully amplified nxrA gene sequences from Nitrococcus mobilis, but not from Nitrospira marina. The second aim was to develop a PCR-DGGE tool to characterize NOB community structure on the basis of Nitrobacter-like partial nrxA gene sequences (Nb-nxrA). We tested (1) the ability of this tool to discriminate between Nitrobacter strains, and (2) its ability to reveal changes in the community structure of NOB harbouring Nb-nrxA sequences induced by light grazing or intensive grazing in grassland soils. The DGGE profiles clearly differed between the four Nitrobacter strains tested. Differences in the structure of NOB community were revealed between grazing regimes. Phylogenetic analysis of the sequences corresponding to different DGGE bands showed that Nb-nxrA sequences did not group in management-specific clusters. Most of the nxrA sequences obtained from soils differed from nxrA sequences of NOB strains. Along with existing tools for characterizing the community structure of nitrifiers, this new approach is a significant step forward to performing comprehensive studies on nitrification.     

Modelling the growth of a methanotrophic biofilm: Estimation of parameters and variability

This article discusses the growth of methanotrophic biofilms. Several independent biofilm growths scenarios involving different inocula were examined. Biofilm growth, substrate removal and product formation were monitored throughout the experiments. Based on the oxygen consumption it was concluded that heterotrophs and nitrifiers co-existed with methanotrophs in the biofilm. Heterotrophic biomass grew on soluble polymers formed by the hydrolysis of dead biomass entrapped in the biofilm. Nitrifier populations developed because of the presence of ammonia in the mineral medium. Based on these experimental results, the computer program AQUASIM was used to develop a biological model involving methanotrophs, heterotrophs and nitrifiers. The modelling of six independent growth experiments showed that stoichiometric and kinetic parameters were within the same order of magnitude. Parameter estimation yielded an average maximum growth rate for methanotrophs, μ_m, of 1.5 ± 0.5 d⁻¹, at 20 °C, a decay rate, b_m, of 0.24 ± 0.1 d⁻¹, a half saturation constant, , of 0.06 ± 0.05 mg CH₄/L, and a yield coefficient, , of 0.57 ±: 0.04 g X/g CH₄. In addition, a sensitivity analysis was performed on this model. It indicated that the most influential parameters were those related to the biofilm (i.e. density; solid-volume fraction; thickness). This suggests that in order to improve the model, further research regarding the biofilm structure and composition is needed.