Conditions Of High Oxygen Concentrations Research Articles

Nitrogen and phosphorus removal by GAOs and PAOs using nitrate and limited oxygen as electron acceptors simultaneously and the impact of external carbon source in the anoxic phase

In this study, the effects of both limited oxygen gradient supplies (0, 0.1–0.3, and 0.3–0.5 mg/L) and nitrate as electron acceptors and an external carbon source in the anoxic phase on nitrogen and phosphorus removal and microbial community structures were investigated. The results demonstrated that more than 90% of the NO3–-N and P removal efficiencies were achieved under limited oxygen conditions (0.1–0.5 mg/L). Improved NH4+-N removal and anaerobic COD uptake were achieved under conditions of high oxygen concentrations. The genera of Dechloromonas (DPAOs) and norank _ f _ Bacteroidetes BD2–2 (PAOs) performed P removal without and with oxygen in the reactor, respectively. The genera of Defluviicoccus and Candidatus Competibacter (GAOs) were mainly responsible for NO3–-N removal in all phases. It indicated that the GAOs and PAOs were responsible for NO3–-N and P removal with a relationship of cooperation besides the competition to carbon source. When there was an external COD in the anoxic phase, the COD and NO3–-N could be removed by the genera of Azospira and Thauera thanks to the heterotrophic denitrification. However, the P removal efficiency decreased as the vicious circle that external COD deteriorated the anoxic P removal and polyhydroxyalkanoates (PHAs) consumption, leading to the decrease of the following anaerobic P release and PHAs synthesis, and more remaining COD. Thus, the anaerobic-anoxic-nitrifying (A2N) process was suggested to be a promising approach for nutrition removal, considering the negative effects of anoxic external COD. Moreover, the formation of granular sludge was promoted under limited oxygen conditions.

Laser ignition and combustion characteristics of micro- and nano-sized boron under different atmospheres and pressures

Boron (B) has potential applications in energetic materials as additive fuel. In order to understand the combustion mechanism of B with various scales, the ignition and combustion characteristics of micro- and nano-sized B under different pressures (0.4 MPa, 0.8 MPa and 1.2 MPa) and atmospheres (60% O2 + 40% N2, 80% O2 + 20% N2 and 100% O2) were studied by a laser ignition and combustion experimental system. The evolution images and specialized parameters of ignition and combustion under different conditions were obtained, and the effects of atmosphere and pressure on the ignition and combustion characteristics of micro- and nano-sized B were discussed. Meanwhile, the crystal structure and morphology of condensed combustion products were observed by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM), and then the compositions in micro-areas were analyzed by energy dispersive X-ray spectroscopy (EDX). The results show that, the burning of micro-sized B is relatively slow, while the burning of nano-sized B is intensified, and a deflagration-like phenomenon is observed for nano-sized B in pure oxygen with pressures of 0.8 and 1.2 MPa. The ignition delay time, combustion time and maximum flame temperature of nano-sized B are smaller than those of micro-sized B, while the maximum characteristic spectral intensity of nano-sized B is stronger. Besides, B2O3, B6O and BN exist in condensed combustion products of micro-sized B, but only B2O3 is detected for nano-sized B, and products agglomerating is observed for nano-sized B. In general, nano-sized B has significant advantages than micro-sized B in the ignition and combustion characteristics, especially under conditions of high oxygen concentrations and high pressures.

Benefit of pulsation in soft corals

Soft corals of the family Xeniidae exhibit a unique, rhythmic pulsation of their tentacles (Movie S1), first noted by Lamarck nearly 200 y ago. However, the adaptive benefit of this perpetual, energetically costly motion is poorly understood. Using in situ underwater particle image velocimetry, we found that the pulsation motions thrust water upward and enhance mixing across the coral-water boundary layer. The induced upward motion effectively prevents refiltration of water by neighboring polyps, while the intensification of mixing, together with the upward flow, greatly enhances the coral's photosynthesis. A series of controlled laboratory experiments with the common xeniid coral Heteroxenia fuscescens showed that the net photosynthesis rate during pulsation was up to an order of magnitude higher than during the coral's resting, nonpulsating state. This enhancement diminished when the concentration of oxygen in the ambient water was artificially raised, indicating that the enhancement of photosynthesis was due to a greater efflux of oxygen from the coral tissues. By lowering the internal oxygen concentration, pulsation alleviates the problem of reduced affinity of ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) to CO2 under conditions of high oxygen concentrations. The photosynthesis-respiration ratio of the pulsating H. fuscescens was markedly higher than the ratios reported for nonpulsating soft and stony corals. Although pulsation is commonly used for locomotion and filtration in marine mobile animals, its occurrence in sessile (bottom-attached) species is limited to members of the ancient phylum Cnidaria, where it is used to accelerate water and enhance physiological processes.

Glutamate Mediates Hyperoxia-Induced Newborn Rat Lung Injury through N-Methyl-D-Aspartate Receptors

Our laboratory found that the N-methyl-D-aspartate receptor (NMDAR) antagonist, MK-801, was able to decrease hyperoxia-induced lung damage. To further search for direct evidence of glutamate and its NMDARs participating in hyperoxia-induced lung injury, the amount of glutamate in the bronchoalveolar lavage fluid and the expression of NMDAR 2D in lung tissue were tracked in newborn rats that were exposed to 95% oxygen for 1, 3, and 7 days. The protective effect of MK-801 was then observed at different hyperoxia exposure times. As demonstrated by RT-PCR, NMDAR 2D expression was much higher in hyperoxia exposure on the third and the seventh days than in the air control group. The levels of glutamate in the bronchoalveolar lavage fluid on the first and third days of hyperoxia exposure were significantly higher than in the air control group. MK-801 alleviated lung injury and inflammatory reaction induced by 95% O(2) for 3 and 7 days. These results indicate that large amounts of endogenous glutamate from the lungs were released, and its NMDAR were expressed strongly under conditions of high oxygen concentration. We conclude that the endogenous glutamate mediated newborn rat lung damage induced by hyperoxia through NMDARs.

Effects of light intensity, oxygen concentration, and carbon dioxide concentration on photosynthesis in algae

The effects of various combinations of light intensity, oxygen concentration, and CO2 concentration on photosynthesis and growth in several algal types were studied. The results suggest the following. (1) Different algae show different responses to high oxygen concentrations and high light intensities. (2) Inhibition of photosynthesis (CO2 fixation and growth), if seen, increases with increasing oxygen concentration and with increasing light intensity (at light intensities greater than saturation). (3) The inhibition of net photosynthesis observed cannot be attributed to high light intensity alone. (4) The inhibition cannot be attributed to increased rates of excretion of organic materials under conditions of high oxygen concentration and high light intensity. (5) Increased concentrations of CO2 can decrease the effect of high oxygen and light in some algae. (6) The decrease in net photosynthesis observed is probably the result of photorespiration. (7) The effect of light intensity, oxygen concentration, or CO2 concentration on algal photosynthesis should not be studied without considering the effect of the other factors. Some implications of these results, as related to primary productivity measurements, are also discussed.

Diffusion studies in viscous media

The rate constants of quenching of the triplet state of naphthalene by α -iodonaphthalene, t -butyl hydroperoxide and oxygen have been studied in several solvents as a function of viscosity and temperature. The diffusion controlled rate constants for α -iodonaphthalene in hydroxylic media agree with those predicted by the equation k calc. = 8 RT /2000 ƞ ( ƞ being viscosity). This is interpreted as evidence for the validity of the Stokes‒Einstein expression, Stoke’s law with ‘slip’ (i. e. coefficient of sliding friction zero) being used for diffusing species comparable in size to the molecules comprising the medium. In liquid paraffin/ n -hexane mixtures, the ratio k obs : k calc. became progressively larger as the proportion of liquid paraffin n -hexane was increased and in 100% liquid paraffin the ratio was 4·5. This is interpreted as being due to breakdown of the Stokes‒Einstein expression in cases where the diffusing species is small compared with the molecules of the solvent. The observed rate constant for quenching by oxygen is also anomalously high, being over 100 times greater than predicted under conditions of high oxygen concentration and high solvent viscosity.