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Use of in-vitro experimental results to model in-situ experiments: bio-denitrification under geological disposal conditions.

Masuda K, Murakami H, Kurimoto Y, Kato O, Kato K, Honda A - Springerplus (2013)

Bottom Line: Among them, reduction by metal compounds and microorganisms seems to be important in the underground repository.Nitrates were reduced almost to N2 gas in the existence of super plasticizer.In the case of humic acids, although nitrates were reduced, the rate was much lower and, in this case, dead organism was used as an electron donor instead of humic acids.

View Article: PubMed Central - PubMed

Affiliation: Kobelco Research Institute Inc, 1-5-5, Takatsuka-dai, Nishi-ku, Kobe, Hyogo, Japan.

ABSTRACT
Some of the low level radioactive wastes from reprocessing of spent nuclear fuels contain nitrates. Nitrates can be present in the form of soluble salts and can be reduced by various reactions. Among them, reduction by metal compounds and microorganisms seems to be important in the underground repository. Reduction by microorganism is more important in near field area than inside the repository because high pH and extremely high salt concentration would prevent microorganism activities. In the near field, pH is more moderate (pH is around 8) and salt concentration is lower. However, the electron donor may be limited there and it might be the control factor for microorganism's denitrification activities. In this study, in-vitro experiments of the nitrate reduction reaction were conducted using model organic materials purported to exist in underground conditions relevant to geological disposal. Two kinds of organic materials were selected. A super plasticizer was selected as being representative of the geological disposal system and humic acid was selected as being representative of pre-existing organic materials in the bedrock. Nitrates were reduced almost to N2 gas in the existence of super plasticizer. In the case of humic acids, although nitrates were reduced, the rate was much lower and, in this case, dead organism was used as an electron donor instead of humic acids. A reaction model was developed based on the in-vitro experiments and verified by running simulations against data obtained from in-situ experiments using actual groundwaters and microorganisms. The simulation showed a good correlation with the experimental data and contributes to the understanding of microbially mediated denitrification in geological disposal systems.

No MeSH data available.


Related in: MedlinePlus

Variation of nitrogen species and microorganism in the presence of humic acid as an electron donor (Run8-11). Initial humic acid concentrations are 0 (small black circles and dotted line), 10 (black marks), 100 (gray marks) and 1000 (white marks) mg/dm3. Other initial conditions are the same: initial concentrations of NO3– and microorganism (Azoarcus tolulyticus) were 50 mmol/dm3and 1000 mg/dm3, respectively. Lines are shown to help identify the general trends shown by the data.
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Fig5: Variation of nitrogen species and microorganism in the presence of humic acid as an electron donor (Run8-11). Initial humic acid concentrations are 0 (small black circles and dotted line), 10 (black marks), 100 (gray marks) and 1000 (white marks) mg/dm3. Other initial conditions are the same: initial concentrations of NO3– and microorganism (Azoarcus tolulyticus) were 50 mmol/dm3and 1000 mg/dm3, respectively. Lines are shown to help identify the general trends shown by the data.

Mentions: In series C (Runs 8–11), tests were carried out using humic acids with A. tolulyticus as the microorganism. Run 8 was a blank test without humic acids and Runs 9–11 were with different concentrations of humic acids. There was no significant difference in the NO3– reduction reaction and the growth of microorganisms between the blank (Run 8) and those with humic acids (Runs 9–11) (Figure 5). In each case, the concentration of microorganisms after eleven days decreased below one tenth of the initial value. By contrast, the activity of A. tolulyticus was confirmed in the experiments in series D (Runs 12 and 13) (Figure 6). In this series, glucose was used in Run 12 because it is easily decomposable in comparison with the humic acid used in Run 13. As shown in Figure 6, NO3– was reduced within two days in the presence of glucose, significantly faster than in the presence of humic acids. This result indicates that A. tolulyticus can adequately reduce NO3– in the presence of easily decomposable organics. It was therefore concluded that no significant denitrification using humic acids could be observed and might be due to a lack of decomposable organics initially introduced. This lack of initial decomposable organics could be a consequence of a dissolved portion of dead microorganisms acting as electron donors instead of the humic acids.Figure 5


Use of in-vitro experimental results to model in-situ experiments: bio-denitrification under geological disposal conditions.

Masuda K, Murakami H, Kurimoto Y, Kato O, Kato K, Honda A - Springerplus (2013)

Variation of nitrogen species and microorganism in the presence of humic acid as an electron donor (Run8-11). Initial humic acid concentrations are 0 (small black circles and dotted line), 10 (black marks), 100 (gray marks) and 1000 (white marks) mg/dm3. Other initial conditions are the same: initial concentrations of NO3– and microorganism (Azoarcus tolulyticus) were 50 mmol/dm3and 1000 mg/dm3, respectively. Lines are shown to help identify the general trends shown by the data.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3755790&req=5

Fig5: Variation of nitrogen species and microorganism in the presence of humic acid as an electron donor (Run8-11). Initial humic acid concentrations are 0 (small black circles and dotted line), 10 (black marks), 100 (gray marks) and 1000 (white marks) mg/dm3. Other initial conditions are the same: initial concentrations of NO3– and microorganism (Azoarcus tolulyticus) were 50 mmol/dm3and 1000 mg/dm3, respectively. Lines are shown to help identify the general trends shown by the data.
Mentions: In series C (Runs 8–11), tests were carried out using humic acids with A. tolulyticus as the microorganism. Run 8 was a blank test without humic acids and Runs 9–11 were with different concentrations of humic acids. There was no significant difference in the NO3– reduction reaction and the growth of microorganisms between the blank (Run 8) and those with humic acids (Runs 9–11) (Figure 5). In each case, the concentration of microorganisms after eleven days decreased below one tenth of the initial value. By contrast, the activity of A. tolulyticus was confirmed in the experiments in series D (Runs 12 and 13) (Figure 6). In this series, glucose was used in Run 12 because it is easily decomposable in comparison with the humic acid used in Run 13. As shown in Figure 6, NO3– was reduced within two days in the presence of glucose, significantly faster than in the presence of humic acids. This result indicates that A. tolulyticus can adequately reduce NO3– in the presence of easily decomposable organics. It was therefore concluded that no significant denitrification using humic acids could be observed and might be due to a lack of decomposable organics initially introduced. This lack of initial decomposable organics could be a consequence of a dissolved portion of dead microorganisms acting as electron donors instead of the humic acids.Figure 5

Bottom Line: Among them, reduction by metal compounds and microorganisms seems to be important in the underground repository.Nitrates were reduced almost to N2 gas in the existence of super plasticizer.In the case of humic acids, although nitrates were reduced, the rate was much lower and, in this case, dead organism was used as an electron donor instead of humic acids.

View Article: PubMed Central - PubMed

Affiliation: Kobelco Research Institute Inc, 1-5-5, Takatsuka-dai, Nishi-ku, Kobe, Hyogo, Japan.

ABSTRACT
Some of the low level radioactive wastes from reprocessing of spent nuclear fuels contain nitrates. Nitrates can be present in the form of soluble salts and can be reduced by various reactions. Among them, reduction by metal compounds and microorganisms seems to be important in the underground repository. Reduction by microorganism is more important in near field area than inside the repository because high pH and extremely high salt concentration would prevent microorganism activities. In the near field, pH is more moderate (pH is around 8) and salt concentration is lower. However, the electron donor may be limited there and it might be the control factor for microorganism's denitrification activities. In this study, in-vitro experiments of the nitrate reduction reaction were conducted using model organic materials purported to exist in underground conditions relevant to geological disposal. Two kinds of organic materials were selected. A super plasticizer was selected as being representative of the geological disposal system and humic acid was selected as being representative of pre-existing organic materials in the bedrock. Nitrates were reduced almost to N2 gas in the existence of super plasticizer. In the case of humic acids, although nitrates were reduced, the rate was much lower and, in this case, dead organism was used as an electron donor instead of humic acids. A reaction model was developed based on the in-vitro experiments and verified by running simulations against data obtained from in-situ experiments using actual groundwaters and microorganisms. The simulation showed a good correlation with the experimental data and contributes to the understanding of microbially mediated denitrification in geological disposal systems.

No MeSH data available.


Related in: MedlinePlus