Nitrite Production Rate Research Articles

Partial nitritation treatment of underground brine waste with high ammonium and salt content

Underground brine waste containing high concentrations of ammonium and with a salinity of 3% is usually generated during the production of methane gas and iodine in the gas field of Chiba Prefecture, Japan. In this study, one swim-bed reactor, packed with a novel acrylic fiber biomass carrier (Biofringe), was applied to the partial nitritation treatment of this kind of underground brine waste. A stable nitrite production rate of 1.6 kg NO(2)-N m(-3) d(-1) was obtained under a nitrogen loading rate of 3.0 kg-N m(-3) d(-1), at a pH of 7.5 and a temperature of 25 degrees C. Nitrate production was negligible and the effluent NO(2)-N/NO(x)-N ratio was above 98% due to the successful inhibition of nitrite-oxidizing bacterial activity. Free ammonia was considered to be the main factor for inhibiting the activity of nitrite-oxidizing bacteria. A microbial community shift was demonstrated by 16S rRNA analysis, and it was shown that the ammonium-oxidizing bacteria became the predominant species after successful nitrite accumulation was observed.

High-rate partial nitrification performance of high ammonium containing wastewater under low temperatures

In this study, a swim-bed reactor was used for partial nitrification treatment of magnesium ammonium phosphate precipitation process treated effluent of methane fermentation digester liquor. Even without temperature, DO, and pH control, the maximum nitrite production rate of 2.66 kg NO 2–N/m 3/d was achieved under a nitrogen loading rate of 5.45 kg N/m 3/d at 18 °C and a nitrite production rate of 0.22 kg NO 2–N/m 3/d was still attained at a nitrogen loading rate of 0.48 kg N/m 3/d even the operational temperature decreased to 8 °C. The average effluent NO 2–N/(NO 2 + NO 3–N) ratio reached 95.4% during the entire experimental period. The mean particle size of suspended sludge increased from 260 to 450 μm and the microscopic observation confirmed the formation of dense-flocs. The results indicated that there were two regimes for ammonium oxidation, one at 20–30 °C and the other at 10–20 °C. Scanning electron microscopic observation and FISH analysis demonstrated that ammonium-oxidizing bacteria were the dominant microorganisms and were considered to be responsible for the satisfactory partial nitrification performance.

Partial nitrification treatment for high ammonium wastewater from magnesium ammonium phosphate process of methane fermentation digester liquor

This study investigated partial nitrification treatment of methane fermentation digester liquor effluent from magnesium ammonium phosphate precipitation process in a swim-bed reactor. The reactor was operated at a temperature of 35 degrees C and pH between 7.5 and 7.8. Partial nitrification was achieved at the onset of the experiments even though conventional activated sludge was used as seed sludge. The maximum nitrite production rate was 1.0 kg NO(2)-N/m(3)/d at a nitrogen loading rate of 2.0 kg-N/m(3)/d. The average effluent NO(2)-N/NH(4)-N ratio and the effluent NO(3)-N concentration were 1.04+/-0.34 and 5.7 mg/l, respectively, during the stable experiment periods. After 150 days of operation, the sludge volume index value decreased to 15 ml/g and the mean particle size of suspended sludge increased by approximately 3 times from 80 to 260 mum. Comparison of mineral analysis between the seed sludge and the partial nitrification sludge demonstrated that the mineral content of the latter increased approximately three-fold in comparison to that of the former. High Ca concentration was considered to be closely related to dense floc formation and superior settleability of the sludge. Both DGGE and DNA clone analysis verified that there were significant microbiological differences between the samples taken at different time periods. Nitrosomonas was confirmed to be the predominant species after stable partial nitrification performance was obtained. The overall results of this study validated our previous results that swim-bed reactor technology could be successfully used as a pre-treatment technology for anammox treatment.

High-rate nitrogen removal from livestock manure digester liquor by combined partial nitritation–anammox process

In this study, combination of a partial nitritation reactor, using immobilized polyethylene glycol (PEG) gel carriers, and a continuous stirred granular anammox reactor was investigated for nitrogen removal from livestock manure digester liquor. Successful nitrite accumulation in the partial nitritation reactor was observed as the nitrite production rate reached 2.1 kg-N/m(3)/day under aerobic nitrogen loading rate of 3.8 kg-N/m(3)/day. Simultaneously, relatively high free ammonia concentrations (average 50 mg-NH(3)/l) depressed the activity of nitrite oxidizing bacteria with nitrate concentration never exceeding 3% of TN concentration in the effluent of the partial nitritation reactor (maximum 35.2 mg/l). High nitrogen removal rates were achieved in the granular anammox reactor with the highest removal rate being 3.12 kg-N/m(3)/day under anaerobic nitrogen loading rate of 4.1 kg-N/m(3)/day. Recalcitrant organic compounds in the digester liquor did not impair anammox reaction and the SS accumulation in the granular anammox reactor was minimal. The results of this study demonstrated that partial nitritation-anammox combination has the potential to successfully remove nitrogen from livestock manure digester liquor.

Ammonia cometabolism and product inhibition vary considerably among species of methanotrophic bacteria

Ecological studies have indicated that relative abundances of Gammaproteobacteria methanotrophs (Gamma-MOB) vs. Alphaproteobacteria methanotrophs (Alpha-MOB) in nitrogen (N) impacted soils are dictated in part by their abilities to tolerate inhibitory effects of ammonium and nitrite. In particular, ammonia is a cometabolic substrate and competitive inhibitor of methane monooxygenase. The rates of ammonia and hydroxylamine oxidation and inhibition of methane-oxidizing activity by ammonium and nitrite were compared among two Gamma-MOB and two Alpha-MOB to determine whether methanotrophs of the same class shared similar physiological profiles. Each isolate exhibited unique K(m(app)) for ammonia and V(max) for nitrite production with or without reductant (methane or sodium formate). The rates of nitrite production from hydroxylamine followed similar trends to rates of ammonia oxidation, indicating that hydroxylamine-oxidizing enzymes were central participants in the ammonia-oxidizing pathway. Methylomonas methanica was incapable of either ammonia or hydroxylamine oxidation. A broad range of sensitivities to ammonium and nitrite inhibition were measured with little consistency between isolates of the same class. The results indicate that physiological responses, and perhaps environmental adaptations, to N compounds are organism specific for methanotrophs.

Effect of Dexamethasone on the Production of Nitric Oxide in Trabecular Meshwork Cells

Purpose: To investigate the effects of dexamethasone (DEX) on the production of nitric oxide (NO) and its enzymatic synthetic pathway in cultured human trabecular meshwork (HTM) cells. Methods: Primarily cultured HTM cells were exposed to 0, 10, 100, 1000 nM of DEX for 3 days. In addition, 100 sepiapterin, 100 ascorbic acid, and 10 methotrexate were co-exposed to DEX. The cellular survival and nitrite production rates were assessed by MTT assay and Griess assay, respectively. Results: DEX did not significantly affect the survival of cultured HTM cells. DEX decreased the NO production in a dosedependent manner. With co-exposure of DEX, ascorbic acid nullified the DEX-induced decrease of NO production. Sepiapterin and methotrexate did not affect DEX-induced decrease of NO production. Conclusions: DEX decreased NO production in HTM cells and the de novo pathway of tetrahydrobiopterin may be involved. This decrease may raise intraocular pressure by decreasing trabecular outflow.

Nitrite Accumulation from Swine Wastewater in a Sequencing Batch Reactor

Shortcut biological nitrogen removal is a process based on nitrification and denitrification via nitrite, rather than nitrate, so both the aeration needed in nitrification and the organic carbon required by denitrifiers can be reduced. This research investigated the possibility of accumulating nitrite in swine wastewater treated in an activated sludge sequencing batch reactor (SBR). The SBR was operated under hydraulic retention times (HRTs) of 3 days and 1.5 days for one month. Ammonium loadings were increased from 0.04 to 0.7 kg NH4-N m-3 d-1. The nitrite/nitrate ratio (NO2/NO3) in the effluent lay mainly within the range of 3 to 4, generating an effluent with 13% to 23% NH4-N, 15% to 21% NO3-N, and 56% to 72% NO2-N. Lower HRT means larger daily feeding volume, which is always preferred if the same treatment efficiency can be obtained. Our results showed that HRT did not affect the composition of effluent nitrogenous compounds, so a longer feeding time would lead to a greater nitrite production rate. Since either or both free ammonia (FA) and free nitrous acid (FNA) were always present at inhibitory levels in the system, a nitrite-dominant effluent could thus be produced from the SBR used in this study with swine wastewater, regardless of the HRT used. The cycle comparison between the two modes with different HRTs with the same ammonium loading rate, 0.058 g NH4+ g-1 MLSS (mixed liquid suspended solid) per day, shows that there is not much difference with regard to the whole nitritation process, which is characterized by continuous conversion of loaded ammonium to nitrite and nitrate in the aerobic feeding period and no further conversion after the loading was terminated, resulting in relatively stable levels for all three nitrogen components in the entire cycle.

Genome-wide transcriptional responses of Nitrosomonas europaea to zinc

Nitrosomonas europaea, a Gram-negative obligate chemolithoautotroph, participates in global nitrogen cycling by carrying out nitrification and derives energy for growth through oxidation of ammonia. In this work, the physiological, proteomic, and transcriptional responses of N. europaea to zinc stress were studied. The nitrite production rate and ammonia-dependent oxygen uptake rate of the cells exposed to 3.4 microM ZnCl2 decreased about 61 and 69% within 30 min, respectively. Two proteins were notably up regulated in zinc treatment and the mRNA levels of their encoding genes started to increase by 1 h after the addition of zinc. A total of 27 genes were up regulated and 30 genes were down regulated. Up-regulated genes included mercury resistance genes (merTPCAD), inorganic ion transport genes, oxidative stress genes, toxin-antitoxin genes, and two-component signal transduction systems genes. merTPCAD was the highest up-regulated operon (46-fold). Down-regulated genes included the RubisCO operon (cbbO), biosynthesis (mrsA), and amino acid transporter.

Potential nitrate removal in a coastal freshwater sediment (Haringvliet Lake, The Netherlands) and response to salinization

Nitrogen transformations and their response to salinization were studied in bottom sediment of a coastal freshwater lake (Haringvliet Lake, The Netherlands). The lake was formed as the result of a river impoundment along the south-western coast of the Netherlands, and is currently targeted for restoration of estuarine conditions. Nitrate porewater profiles indicate complete removal of NO 3 - within the upper few millimeters of sediment. Rapid NO 3 - consumption is consistent with the high potential rates of nitrate reduction (up to 200 nmol N cm −3 h −1) measured with flow-through reactors (FTRs) on intact sediment slices. Acetylene-block FTR experiments indicate that complete denitrification accounts for approximately half of the nitrate reducing activity. The remaining NO 3 - reduction is due to incomplete denitrification and alternative reaction pathways, most likely dissimilatory nitrate reduction to NH 4 + (DNRA). Results of FTR experiments further indicate that increasing bottom water salinity may lead to a transient release of NH 4 + and dissolved organic carbon from the sediment, and enhance the rates of nitrate reduction and nitrite production. Increased salinity may thus, at least temporarily, increase the efflux of NH 4 + from the sediment to the surface water. This work shows that salinity affects the relative importance of denitrification compared to alternative nitrate reduction pathways, limiting the ability of denitrification to remove bioavailable nitrogen from aquatic ecosystems.

Bacterial Flavodoxins Support Nitric Oxide Production by Bacillus subtilis Nitric-oxide Synthase

Unlike animal nitric-oxide synthases (NOSs), the bacterial NOS enzymes have no attached flavoprotein domain to reduce their heme and so must rely on unknown bacterial proteins for electrons. We tested the ability of two Bacillus subtilis flavodoxins (YkuN and YkuP) to support catalysis by purified B. subtilis NOS (bsNOS). When an NADPH-utilizing bacterial flavodoxin reductase (FLDR) was added to reduce YkuP or YkuN, both supported NO synthesis from either L-arginine or N-hydroxyarginine and supported a linear nitrite accumulation over a 30-min reaction period. Rates of nitrite production were directly dependent on the ratio of YkuN or YkuP to bsNOS. However, the V/Km value for YkuN (5.2 x 10(5)) was about 20 times greater than that of YkuP (2.6 x 10(4)), indicating YkuN is more efficient in supporting bsNOS catalysis. YkuN that was either photo-reduced or prereduced by FLDR transferred an electron to the bsNOS ferric heme at rates similar to those measured for heme reduction in the animal NOSs. YkuN supported a similar NO synthesis activity by a different bacterial NOS (Deinococcus radiodurans) but not by any of the three mammalian NOS oxygenase domains nor by an insect NOS oxygenase domain. Our results establish YkuN as a kinetically competent redox partner for bsNOS and suggest that FLDR/flavodoxin proteins could function physiologically to support catalysis by bacterial NOSs.

Stoichiometric and kinetic characterisation of Nitrosomonas sp. in mixed culture by decoupling the growth and energy generation processes

A novel method that relies on the decoupling of the energy production and biosynthesis processes was used to characterise the maintenance, cell lysis and growth processes of Nitrosomonas sp. A Nitrosomonas culture was enriched in a sequencing batch reactor (SBR) with ammonium as the sole energy source. Fluorescent in situ hybridization (FISH) showed that Nitrosomonas bound to the NEU probe constituted 82% of the bacterial population, while no other known ammonium or nitrite oxidizing bacteria were detected. Batch tests were carried out under conditions that both ammonium and CO2 were in excess, and in the absence of one of these two substrates. The oxygen uptake rate and nitrite production rate were measured during these batch tests. The results obtained from these batch tests, along with the SBR performance data, allowed the determination of the maintenance coefficient and the in situ cell lysis rate, as well as the maximum specific growth rate of the Nitrosomonas culture. It is shown that, during normal growth, the Nitrosomonas culture spends approximately 65% of the energy generated for maintenance. The maintenance coefficient was determined to be 0.14-0.16 mgN mgCOD(biomass)(-1)h(-1), and was shown to be independent of the specific growth rate. The in situ lysis rate and the maximum specific growth rate of the Nitrosomonas culture were determined to be 0.26 and 1.0 day(-1) (0.043 h(-1)), respectively, under aerobic conditions at 30 degrees C and pH 7.

Evaluation of bacterial nitrate reduction in the human oral cavity

It is hypothesized that the enterosalivary nitrate circulation encourages nitrate reducing bacteria to reside within the oral cavity. Nitrite production may then limit the growth of acidogenic bacteria as a result of the production of antimicrobial oxides of nitrogen, including nitric oxide. This study was carried out with 10 subjects to characterize oral nitrate reduction and identify the bacteria responsible. Nitrate reduction varied between individuals (mean 85.4 +/- 15.9 nmol nitrite min(-1) with 10 ml 1 mm KNO(3) mouth wash) and was found to be concentrated at the rear of the tongue dorsal surface. Nitrate reductase positive isolates identified, using 16S rDNA sequencing, from the tongue comprised Veillonella atypica (34%), Veillonella dispar (24%), Actinomyces odontolyticus (21%), Actinomyces naeslundii (2%), Rothia mucilaginosa (10%), Rothia dentocariosa (3%) and Staphylococcus epidermidis (5%). Nitrite production rates, using intact and permeabilized cells, of the major tongue nitrate reducers were determined in the presence of methyl and benzyl viologen. Under anaerobic conditions in the presence of nitrate, rates in decreasing order were: A. odontolyticus > R. mucilaginosa > R. dentocariosa > V. dispar > V. atypica. In conclusion, Veillonella spp. were found to be the most prevalent taxa isolated and thus may make a major contribution to nitrate reduction in the oral cavity.

Difficulties in maintaining long-term partial nitritation of ammonium-rich sludge digester liquids in a moving-bed biofilm reactor (MBBR)

Nitrogen can be eliminated effectively from sludge digester effluents by anaerobic ammonium oxidation (anammox), but 55-60% of the ammonium must first be oxidized to nitrite. Although a continuous flow stirred tank reactor (CSTR) with suspended biomass could be used, its hydraulic dilution rate is limited to 0.8-1 d(-1) (30 degrees C). Higher specific nitrite production rates can be achieved by sludge retention, as shown here for a moving-bed biofilm reactor (MBBR) with Kaldnes carriers on laboratory and pilot scales. The maximum nitrite production rate amounted to 2.7 gNO2-Nm(-2)d(-1) (3 gO2m(-3)d(-1), 30.5 degrees C), thus doubling the dilution rate compared to CSTR operation with suspended biomass for a supernatant with 700 gNH4-Nm(-3). Whenever the available alkalinity was fully consumed, an optimal amount of nitrite was produced. However, a significant amount of nitrate was produced after 11 months of operation, making the effluent unsuitable for anaerobic ammonium oxidation. Because the sludge retention time (SRT) is relatively long in biofilm systems, slow growth of nitrite oxidizers occurs. None of the selection criteria applied - a high ammonium loading rate, high free ammonia or low oxygen concentration - led to selective suppression of nitrite oxidation. A CSTR or SBR with suspended biomass is consequently recommended for full-scale operation.

Characterization of the magnitude and kinetics of xanthine oxidase-catalyzed nitrate reduction: evaluation of its role in nitrite and nitric oxide generation in anoxic tissues.

In addition to nitric oxide (NO) generation from specific NO synthases, NO is also formed during anoxia from nitrite reduction, and xanthine oxidase (XO) catalyzes this process. While in tissues and blood high nitrate levels are present, questions remain regarding whether nitrate is also a source of NO and if XO-mediated nitrate reduction can be an important source of NO in biological systems. To characterize the kinetics, magnitude, and mechanism of XO-mediated nitrate reduction under anaerobic conditions, EPR, chemiluminescence NO-analyzer, and NO-electrode studies were performed. Typical XO reducing substrates, xanthine, NADH, and 2,3-dihydroxybenz-aldehyde, triggered nitrate reduction to nitrite and NO. The rate of nitrite production followed Michaelis-Menten kinetics, while NO generation rates increased linearly following the accumulation of nitrite, suggesting stepwise-reduction of nitrate to nitrite then to NO. The molybdenum-binding XO inhibitor, oxypurinol, inhibited both nitrite and NO production, indicating that nitrate reduction occurs at the molybdenum site. At higher xanthine concentrations, partial inhibition was seen, suggesting formation of a substrate-bound reduced enzyme complex with xanthine blocking the molybdenum site. The pH dependence of nitrite and NO formation indicate that XO-mediated nitrate reduction occurs via an acid-catalyzed mechanism. With conditions occurring during ischemia, myocardial xanthine oxidoreductase and nitrate levels were determined to generate up to 20 microM nitrite within 10-20 min that can be further reduced to NO with rates comparable to those of maximally activated NOS. Thus, XOR catalyzed nitrate reduction to nitrite and NO occurs and can be an important source of NO production in ischemic tissues.

GL&V says Eimco integration 75% complete

A pilot-scale bioslurry system was used to test the treatment of soils highly contaminated with 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT). The treatment scheme involved a soil-washing process followed by two sequential aerobic slurry reactors augmented with 2,4-DNT- and 2,6-DNT-mineralizing bacteria. Test soils were obtained from two former army ammunition plants, the Volunteer Army Ammunition Plant (VAAP, Chattanooga, TN) and the Badger Army Ammunition Plant (BAAP, Baraboo, WI). Soil washing was used to minimize operational problems in slurry reactors associated with large particulates. The Eimco slurry reactors were operated in a draw-and-fill mode for 3 months and were monitored for the biodegradation of 2,4-DNT and 2,6-DNT, nitrite production, NaOH consumption, and oxygen uptake rate. Results show that soil washing was very effective for the removal of sands and the recovery of soil fines containing 2,4-DNT and 2,6-DNT. Bioslurry reactors offered rapid and nearly complete degradation of both DNT isomers, but require real time monitoring to avoid long lag periods upon refeeding. Results found a significant discrepancy between the measured DNT concentrations and calculated DNT concentrations in the slurry reactors because of solids profiles in the slurry reactors and the presence of floating crystal of DNTs. Based on the actual amount of dinitrotoluene degradation, nitrite release, NaOH consumption, and oxygen uptake were close to the theoretical stoichiometric coefficients of complete DNT mineralization. Such stoichiometric relationships were not achieved if the calculation was based on the measured DNT concentrations due to the heterogeneity of DNT in the reactor. Results indicate that nitrite release, NaOH consumption, and oxygen uptake rates provide a fast assessment of 2,4-DNT degradation and microbial activity in a slurry reactor, but could not be extended to a second reactor in series where the degradation of a much lower concentration of 2,6-DNT degradation was achieved.

Evidence that RDX biodegradation by Rhodococcus strain DN22 is plasmid-borne and involves a cytochrome p-450.

To investigate the biodegradation of the explosive compound RDX in Rhodococcus strain DN22, a bacterium previously isolated for its ability to grow on RDX as sole nitrogen source. Analysis of the rates of RDX degradation and nitrite production indicated that 2 mol nitrite were produced per mole RDX degraded. Cells of strain DN22 had the highest activity against RDX during the exponential phase and low activity in the stationary phase. Nitrite production from RDX was inhibited by metyrapone, menadione, piperonyl butoxide, n-octylamine and carbon monoxide and inducible by pyrrolidine, pyridine and atrazine. Acridine orange treatment yielded RDX-minus derivatives of strain DN22 at a curing rate of 1.5% and all of the cured derivatives had lost a large plasmid. RDX biodegradation in strain DN22 appears to involve a plasmid-encoded cytochrome p-450 enzyme. Plasmid-borne RDX degradation genes could potentially be transferred between bacteria. Our research into RDX metabolism in strain DN22 will facilitate future applications of this bacterium for bioremediation.

Modeling Enhanced In Situ Denitrification in Groundwater

A two-dimensional numerical solute transport model was developed for simulating an enhanced in situ denitrification experi- ment performed in a nitrate-contaminated aquifer on Cape Cod, Massachusetts. In this experiment, formate ~HCOO 2 ! was injected for a period of 26 days into the carbon-limited aquifer to stimulate denitrification. Calibration of the vertical-profile site model was demon- strated through error analysis and comparison with formate, nitrate, and nitrite concentration data monitored along a transect of three multilevel groundwater sampling wells for 75 days after initial injection. Formate utilization rates were approximately 142 and 38 mM/day for nitrate and nitrite reduction, respectively. Nitrate and nitrite utilization rates were approximately 29 and 8 mM/day, respectively. Nitrate utilization rates under enhanced conditions were 1 order of magnitude greater than previously reported naturally occurring rates. The nitrite production rate was approximately 29 mM/day. Persistence of nitrite was attributed to a combination of factors, including electron donor ~formate! limitation late in the experiment, preferential utilization of nitrate as an electron acceptor, and greater nitrite production relative to nitrite utilization.

Seasonal variations in uptake and in situ regeneration of nitrogen in mangrove waters

Seasonal changes of uptake of nitrogenous nutrients (NH4+, NO3−, NO2−, and urea) and regeneration (NH4+ and NO2− production) in the plankton fraction of a mangrove ecosystem on the west coast of India were investigated. Nitrate was the major fraction of assimilable N (72%), followed by NH4+ (16%), NO2− (6%), and urea (6%). Changes of nutrient concentrations followed clear seasonal cycles and were mainly regulated by in situ biological processes. The plankton took up NO3− and NH4+ in more or less equal proportions (39 and 44% respectively), followed by urea (11%) and NO2− (6%). Seasonal patterns of uptake were distinct, with a dominance of NO3− and NO uptake in the postmonsoon, followed by a dominance of NH4+ and urea uptake in the premonsoon. The high and prolonged use of NO3− at the beginning of the productive season was due to a strong allochthonous supply of NO3−, dominance of microplankton, and low NH4+ regeneration rates. Heterotrophs may take up all four nutrients and could account for half of the annual total N uptake. Ammonium and NO2− regeneration rates were among the highest known from nearshore waters and showed clear seasonal patterns. Production and use of NH4+ were closely coupled. Nitrite production rates were related to NH4+ production rates in a rectangular‐hyperbolic fit. Nitrogen balance analyses showed that proximity to mangrove vegetation enhanced the flux rates, noninclusion of nitrification may lead to an overestimation of new production by 30%, and regeneration in the plankton fraction provided about 40% more N than was assimilated.

Remediation of dinitrotoluene contaminated soils from former ammunition plants: soil washing efficiency and effective process monitoring in bioslurry reactors

A pilot-scale bioslurry system was used to test the treatment of soils highly contaminated with 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT). The treatment scheme involved a soil-washing process followed by two sequential aerobic slurry reactors augmented with 2,4-DNT- and 2,6-DNT-mineralizing bacteria. Test soils were obtained from two former army ammunition plants, the Volunteer Army Ammunition Plant (VAAP, Chattanooga, TN) and the Badger Army Ammunition Plant (BAAP, Baraboo, WI). Soil washing was used to minimize operational problems in slurry reactors associated with large particulates. The Eimco slurry reactors were operated in a draw-and-fill mode for 3 months and were monitored for the biodegradation of 2,4-DNT and 2,6-DNT, nitrite production, NaOH consumption, and oxygen uptake rate. Results show that soil washing was very effective for the removal of sands and the recovery of soil fines containing 2,4-DNT and 2,6-DNT. Bioslurry reactors offered rapid and nearly complete degradation of both DNT isomers, but require real time monitoring to avoid long lag periods upon refeeding. Results found a significant discrepancy between the measured DNT concentrations and calculated DNT concentrations in the slurry reactors because of solids profiles in the slurry reactors and the presence of floating crystal of DNTs. Based on the actual amount of dinitrotoluene degradation, nitrite release, NaOH consumption, and oxygen uptake were close to the theoretical stoichiometric coefficients of complete DNT mineralization. Such stoichiometric relationships were not achieved if the calculation was based on the measured DNT concentrations due to the heterogeneity of DNT in the reactor. Results indicate that nitrite release, NaOH consumption, and oxygen uptake rates provide a fast assessment of 2,4-DNT degradation and microbial activity in a slurry reactor, but could not be extended to a second reactor in series where the degradation of a much lower concentration of 2,6-DNT degradation was achieved.

Alterations in relaxation to lactate and H(2)O(2) in human placental vessels from gestational diabetic pregnancies.

We determined whether alterations in the mechanism of relaxation to H(2)O(2) potentially contribute to the enhanced prostaglandin-mediated contractile response to H(2)O(2) and posthypoxic reoxygenation seen in human placental vessels of pregnancies with gestational diabetes mellitus (GDM). Isolated placental arteries and veins from GDM and uncomplicated full-term pregnancies were precontracted with prostaglandin F(2alpha) (PO(2) 35-38 Torr) and then exposed to lactate (1-10 mM), arachidonic acid (0.01-10 microM), nitroglycerin (1 nM-1 microM), forskolin (0.01-10 microM), or H(2)O(2) (1 microM-1 mM + 10 microM indomethacin). The rates of tissue H(2)O(2) metabolism by catalase and nitrite production were measured. The relaxation to lactate was reduced in GDM placental arteries and veins by 54-85 and 66-80%, and the relaxation to H(2)O(2) was inhibited by 80-94% in GDM placental veins compared with vessels from uncomplicated full-term pregnancies. H(2)O(2) caused only minimal relaxation of placental arteries. Responses to other relaxing agents were not altered in the GDM placental vessels. Diabetic vessels showed rates of nitrite production that were increased by 113-195% and rates of H(2)O(2) metabolism by catalase that were decreased by 44-61%. The loss of relaxation to H(2)O(2) and lactate (mediated via H(2)O(2)), perhaps as a result of the inhibition of catalase by nitric oxide, may explain the previously reported enhancement of prostaglandin-mediated contractile responses to H(2)O(2) and posthypoxic reoxygenation seen in GDM placental vessels.