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

1994 ◽  
Vol 30 (6) ◽  
pp. 91-100 ◽  
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.

Inhibitors of Tyrosinase

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.

Investigation of Fluoride Tolerance in Acidithiobacillus ferrooxidans

2017 ◽  
Vol 262 ◽  
pp. 452-455
Author(s):  
Jie Meng Tao ◽  
Li Yuan Ma ◽  
Chong Qin ◽  
Hua Qun Yin ◽  
Yi Li Liang ◽  
...  
Keyword(s):  
Acidithiobacillus Ferrooxidans ◽  
Reduction Potential ◽  
Fluoride Concentration ◽  
Ferric Ions ◽  
Fluoride Ions ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Low Concentrations ◽  
Ion Species ◽  
Delayed Time

Anionic ion species occur in gangue minerals and impact the bioleaching efficiency even at low concentrations. Recently, the detrimental influence of fluoride ions on bioleaching microorganisms has caused great attention in research. However, the tolerance mechanisms of bioleaching microorganisms for fluoride are still unclear. In order to reveal fluoride tolerance, culture experiments with different concentrations of fluoride and ferrous iron-grown Acidithiobacillus ferrooxidans were carried out. The results showed that oxidation-reduction potential, oxidation capacity of iron and cell density were all negatively correlated to the fluoride concentration. The growth of A. ferrooxidans showed a longer delayed time and a slower growth rate when fluoride concentration increased. The fluoride tolerance for A. ferrooxidans could be attributed to the generated ferric ions from ferrous oxidation. Ferric ions reacted with HF to decrease the concentration of F- and finally reduced the toxicity of fluoride on A. ferrooxidans.

Improving the sensitivity of the activated sludge respiration inhibition test and verifying the results using an oxidation-reduction potential electrode

2016 ◽  
Vol 75 (2) ◽  
pp. 247-254 ◽  
Author(s):  
F. Friedrichs ◽  
K. U. Rudolph ◽  
Bich Hanh Nguyen ◽  
D. Meinardi ◽  
W. Genthe ◽  
...  
Keyword(s):  
Activated Sludge ◽  
Oxygen Sensor ◽  
Reduction Potential ◽  
Treatment Plant ◽  
Inhibition Test ◽  
Synthetic Wastewater ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Potential Electrode ◽  
Nutrient Solutions

The inhibition of activated sludge respiration is one of the most important parameters for monitoring wastewater toxicity. The main objective of this study was to improve respiration inhibition testing in order to protect the biological degradation within the aerobic process in a wastewater treatment plant more efficiently. In order to influence the sensitivity of the testing bacteria, two different nutrient solutions were selected for biological testing, synthetic wastewater according to ISO 8192 and NaAc (sodium acetate). The effects of the nutrient solutions on heavy metal speciation and their respiration inhibition were investigated. The toxicants Zn(II), Cu(II), Cr(VI) and 3,5 DCP (3,5-dichlorophenol) were used as standards to determine toxicities and to study the influence of nutrient solutions. Results have shown that NaAc as a nutrient solution sensitized the respiration inhibition test up to a factor of 7.7. Furthermore, an oxidation reduction potential electrode can be used as an alternative tool to verify the results obtained with an oxygen sensor.

Sign in / Sign up

Export Citation Format

Share Document