Tolerance of Theora fragilis(Bivalvia: Semelidae) to Low Concentrations of Dissolved Oxygen.

Based on the Jihogntan reservoir’s monitoring data from 2006 to 2009, eutrophication of Jihongtan reservoir was assessed. The result showed that the nutrition level of the Jihongtan reservoir was middle in recent years. The average concentration of chlorophyll-a(Chla) was higher in summer and autumn than in spring and winter. The correlation between concentration of Chla and some environmental factors was studied by statistical method, and seasonal variation of Chla and the extent of eutrophication were also analyzed. The results showed that the correlations between Chla and total nitrogen(TN), dissolved oxygen(DO) and transparency were significantly negative, and that between Chla and total phosphorus(TP), temperature(T) and potassium permanganate index(COD Mn) were significantly positive. The growth of phytoplankton was promoted by TP and TN at low concentrations, and inhibited by TN at high concentrations.

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Geochemistry of contrasting stream types, Taylor Valley, Antarctica

Geological Society of America Bulletin ◽

10.1130/b35479.1 ◽

2020 ◽

Vol 133 (1-2) ◽

pp. 425-448

Author(s):

Russell S. Harmon ◽

Deborah L. Leslie ◽

W. Berry Lyons ◽

Kathleen A. Welch ◽

Diane M. McKnight

Keyword(s):

Dissolved Oxygen ◽

Austral Summer ◽

Mineral Dissolution ◽

Silicate Mineral ◽

Cation Composition ◽

Taylor Valley ◽

Low Concentrations ◽

Hyporheic Zones ◽

Dry Valley ◽

Geochemical Fingerprint

Abstract The McMurdo Dry Valley region is the largest ice-free area of Antarctica. Ephemeral streams flow here during the austral summer, transporting glacial meltwater to perennially ice-covered, closed basin lakes. The chemistry of 24 Taylor Valley streams was examined over the two-decade period of monitoring from 1993 to 2014, and the geochemical behavior of two streams of contrasting physical and biological character was monitored across the seven weeks of the 2010–2011 flow season. Four species dominate stream solute budgets: HCO3–, Ca2+, Na+, and Cl–, with SO42–, Mg2+, and K+ present in significantly lesser proportions. All streams contain dissolved silica at low concentrations. Across Taylor Valley, streams are characterized by their consistent anionic geochemical fingerprint of HCO3 > Cl > SO4, but there is a split in cation composition between 14 streams with Ca > Na > Mg > K and 10 streams with Na > Ca > Mg > K. Andersen Creek is a first-order proglacial stream representative of the 13 short streams that flow <1.5 km from source to gage. Von Guerard is representative of 11 long streams 2–7 km in length characterized by extensive hyporheic zones. Both streams exhibit a strong daily cycle for solute load, temperature, dissolved oxygen, and pH, which vary in proportion to discharge. A well-expressed diurnal co-variation of pH with dissolved oxygen is observed for both streams that reflects different types of biological control. The relative consistency of Von Guerard composition over the summer flow season reflects chemostatic regulation, where water in transient storage introduced during times of high streamflow has an extended opportunity for water-sediment interaction, silicate mineral dissolution, and pore-water exchange.

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Influence of denitrification reactor retention time distribution (RTD) on dissolved oxygen control and nitrogen removal efficiency

Water Science & Technology ◽

10.2166/wst.2015.188 ◽

2015 ◽

Vol 72 (1) ◽

pp. 45-51 ◽

Cited By ~ 14

Author(s):

Massimo Raboni ◽

Renato Gavasci ◽

Paolo Viotti

Keyword(s):

Dissolved Oxygen ◽

Removal Efficiency ◽

Nitrogen Removal ◽

Plug Flow ◽

Oxygen Control ◽

Low Concentrations ◽

Dissolved Oxygen Control ◽

Denitrification Reactor ◽

Do Concentration ◽

Mixed Reactor

Abstract Low concentrations of dissolved oxygen (DO) are usually found in biological anoxic pre-denitrification reactors, causing a reduction in nitrogen removal efficiency. Therefore, the reduction of DO in such reactors is fundamental for achieving good nutrient removal. The article shows the results of an experimental study carried out to evaluate the effect of the anoxic reactor hydrodynamic model on both residual DO concentration and nitrogen removal efficiency. In particular, two hydrodynamic models were considered: the single completely mixed reactor and a series of four reactors that resemble plug-flow behaviour. The latter prove to be more effective in oxygen consumption, allowing a lower residual DO concentration than the former. The series of reactors also achieves better specific denitrification rates and higher denitrification efficiency. Moreover, the denitrification food to microrganism (F:M) ratio (F:MDEN) demonstrates a relevant synergic action in both controlling residual DO and improving the denitrification performance.

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Inhibitors of Tyrosinase

Journal of Experimental Biology ◽

10.1242/jeb.32.3.468 ◽

1955 ◽

Vol 32 (3) ◽

pp. 468-484

Author(s):

M. G. M. PRYOR

Keyword(s):

Methylene Blue ◽

Dissolved Oxygen ◽

Inhibitory Effect ◽

Tyrosinase Activity ◽

Aromatic Substrate ◽

Oxidation Reduction ◽

Oxidation Reduction Potential ◽

Low Concentrations ◽

Sulphydryl Groups

1. It has been reported that if Drosophila larvae are ground to a fine paste with sand, the homogenate shows little tyrosinase activity, but that if the larvae are allowed to blacken in chloroform vapour before grinding, activity is increased. 2. This has been interpreted as showing the effect of an intracellular inhibitor, set free by rupturing the cells, but destroyed by chloroform. This inhibitor has been identified by previous authors as a dehydrogenase. 3. It is here suggested that the lack of activity of Drosophila extracts prepared with sand is due to destruction of tyrosinase as it oxidizes naturally occurring aromatic substrates. 4. It is shown that tyrosinase is destroyed by oxidizing the aromatic substrate present in the cuticle of Calliphora larvae, or by very low concentrations of homocatechol. 5. The aromatic substrate of Calliphora larvae is concentrated in the cuticle, and would be set free by fine grinding. 6. Drosophila or Calliphora larvae yield a more active extract when ground with sand than when simply crushed, provided that they are tested soon after grinding. 7. The tyrosinase activity of such extracts is not increased by chloroform or methanol. 8. The compound between o-quinones and amino-acids is capable of oxidizing ascorbic acid or excess amino-acid without the aid of an enzyme, and of simultaneously reducing methylene blue. 9. This reaction, rather than the activity of dehydrogenases, is probably responsible for most of the ability of damaged insect tissue to bleach methylene blue. 10. The blood of insects normally contains dissolved oxygen in equilibrium with the air. 11. The reaction involved in the blackening of insect blood may consume all the dissolved oxygen. 12. Previous observations on fluctuations in the oxidation-reduction potential of the blood of Calliphora larvae with age are probably due to changes in the rate at which oxygen is consumed by the blood after it is shed. 13. There does not therefore appear to be any valid evidence that tyrosinase is inhibited in vivo by the action of dehydrogenases. The absence of tyrosinase activity in undamaged tissue is probably due to the structure of the cytoplasm, which keeps enzyme and substrate apart. 14. Instances of the inhibition of tyrosinase reported in Crustacea and Echinodermata seem to be susceptible of the same explanation as in insects. 15. The supposed inhibitory effect of sulphydryl groups reported for vertebrate melanophores is shown to be due to the combination of sulphydryl groups with o-quinones, which prevents the formation of melanins.

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Colorimetric Determination of Low Concentrations of Dissolved Oxygen in Water

Analytical Chemistry ◽

10.1021/ac60105a011 ◽

1955 ◽

Vol 27 (9) ◽

pp. 1401-1404 ◽

Cited By ~ 9

Author(s):

L. S. Buchoff ◽

N. M Ingber ◽

J. H. Brady

Keyword(s):

Dissolved Oxygen ◽

Colorimetric Determination ◽

Low Concentrations

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Characteristics of Low-Oxygen Oxidation Ditch with Improved Nitrogen Removal

Water ◽

10.3390/w13243603 ◽

2021 ◽

Vol 13 (24) ◽

pp. 3603

Author(s):

Elena Gogina ◽

Igor Gulshin

Keyword(s):

Dissolved Oxygen ◽

Activated Sludge ◽

Settling Tank ◽

Reaction Rates ◽

Organic Load ◽

Pcr Analysis ◽

Low Oxygen ◽

Low Concentrations ◽

The Stability ◽

Oxygen Oxidation

This article presents a study on the operational stability of laboratory oxidation ditches, designated for synthetic and real wastewater and operable at low concentrations of dissolved oxygen. The project encompassed the stability monitoring of activated sludge depending on sedimentation characteristics and hydrobiological indicator microorganisms, determining (1) the size of sludge floccules and (2) the main functional groups of microorganisms identified in the course of the PCR analysis and reaction rates, plotted using the Michaelis–Menten enzymatic kinetics for the mixed culture biomass. The most stable system involves a bioreactor featuring dissolved oxygen gradients that range from 1.9 to 0.15 mg/L s, a specific organic load of 0.21 gBOD/g/d and a hydraulic retention time of 12 h. A built-in settling tank allows the consideration of the potential generation of large floccules of activated sludge in oxidation ditches (at least 300 μm) that increase the efficiency of simultaneous nitrification and denitrification. Thus, the obtained reaction rates can be used in calculations and simulations of the operation of oxidation ditches at low concentrations of dissolved oxygen.

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Investigation of oxidizing polymerization processes at high velocities of initiation in technique of laser stereolithography

Science intensive technologies in mechanical engineering ◽

10.12737/21238 ◽

2016 ◽

Vol 1 (9) ◽

pp. 37-41

Author(s):

Илья Малов ◽

Ilya Malov

Keyword(s):

Dissolved Oxygen ◽

Induction Period ◽

Laser Emission ◽

Visible Range ◽

Reaction Products ◽

Track Formation ◽

Low Concentrations ◽

Anti Oxidant ◽

High Concentrations ◽

Laser Stereolithography

The paper deals with the investigation of polymerization processes in acryl compositions which were developed first for stereolithography using a promising photo-initiating laser emission of a visible range. The processes of oxidizing polymerization of a photo-polymerizing composition at very low concentrations of an antioxidant [X] and a concentration of dissolved oxygen [O2] > 10-7 ÷ 10-8 mole/l are considered. It is shown that the appearance of an induction period is typical just of reactions passing in a closed system, and in an open one a reaction passes without an induction period. Under these conditions the reaction products are poly-peroxides of a low-molecular structure. There are also considered the processes of polymerization at the dissolved oxygen concentration [O2] > 10-7 ÷ 10-8 mole/l and at high concentrations of anti-oxidant X. It is determined that after a lapse of time when an oxidant is spent a velocity of oxygen expense increases as a result of which in the layers more remote from the boundary of phase division the composition – air the open system transforms into a closed one. In these layers the rate of oxygen diffusion appeared to be less of the rate of its expense in reactions of monomer oxidation. The investigation results explain the mechanism of a track formation at the irradiation of a photo-polymerizing composition with a laser beam.

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Influence of dissolved oxygen and oxidation–reduction potential on the denitrification rate of activated sludge

Water Science & Technology ◽

10.2166/wst.1994.0256 ◽

1994 ◽

Vol 30 (6) ◽

pp. 91-100 ◽

Cited By ~ 23

Author(s):

Ewa Lie ◽

Thomas Welander

Keyword(s):

Dissolved Oxygen ◽

Activated Sludge ◽

Reduction Potential ◽

Inhibitory Effect ◽

Denitrification Rate ◽

Oxidation Reduction ◽

Oxidation Reduction Potential ◽

Low Concentrations ◽

Denitrification Activity ◽

Do Concentration

The influence of low concentrations of dissolved oxygen (DO) and the oxidation-reduction potential (ORP) on the denitrification activity of activated sludge has been studied in batchwise experiments. The ORP was maintained at different levels by automatic titration with air and the denitrification activity was determined by following the disappearance of nitrate. Oxygen was found to have a negative effect on denitrification even at lower concentrations than can be measured with conventional oxygen probes (<0.1 mg/L). The ORP was found to be a useful indicator of the DO concentration at this low level and the denitrification rate was found to decrease linearly with increasing ORP. However, the effect of the ORP on denitrification differed between sludges from different treatment plants. A linear relationship was also found between the ORP and the DO concentration in the region of measurable DO concentrations. Extrapolation of this straight line into the region where DO was under the detection limit indicated that oxygen exerts an inhibitory effect on denitrification at such low concentrations as a few μg/L.

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