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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

Comparison of nitrate utilization and nitrogen gas evolved with and without super plasticizer as an electron donor in 1.0 mmol/dm3of nitrate solutions and 1000 mg/dm3of activated sludge as the microorganism. Run 2 was carried out with the electron donor and Run1 was carried out without the electron donor (blank). 2N2 is used for amount of N2 evolved in order to directly compare the mass balance with NO3-.Lines are shown to help identify the general trends shown by the data.
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Fig1: Comparison of nitrate utilization and nitrogen gas evolved with and without super plasticizer as an electron donor in 1.0 mmol/dm3of nitrate solutions and 1000 mg/dm3of activated sludge as the microorganism. Run 2 was carried out with the electron donor and Run1 was carried out without the electron donor (blank). 2N2 is used for amount of N2 evolved in order to directly compare the mass balance with NO3-.Lines are shown to help identify the general trends shown by the data.

Mentions: In series A, Run 1 was run as a blank and Run 2 contained super plasticizer in order to elucidate the potential of super plasticizer as an electron donor on the behavior of NO3– reduction using activated sludge as the microorganism. The temporal changes in the composition of nitrogen compounds in Run 1 and Run 2 are shown in Figure 1. Although NO3– was consumed in the blank test (Run 1), more NO3– was reduced to produce more N2 by the presence of super plasticizers (Run 2). The consumption of NO3– in the blank test will be discussed in more detail later. The material balance of nitrogen classified according to species (NO3–, NO2–, NH3, N2 or solid phase [Nsolid]) is shown in Figure 2. Nsolid was calculated from nitrogen contents of the solid fraction. In the Figure 2, 2N2 was used for direct comparison in atomic nitrogen base. In Run 2, NO3– initially accounted for all nitrogen not in the solid phase. The production of NH3 and the appearance of NO2– was limited to the first 6 days of reaction. Consequently, the NO3– decrease could be broadly correlated with the production of N2.Figure 1


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)

Comparison of nitrate utilization and nitrogen gas evolved with and without super plasticizer as an electron donor in 1.0 mmol/dm3of nitrate solutions and 1000 mg/dm3of activated sludge as the microorganism. Run 2 was carried out with the electron donor and Run1 was carried out without the electron donor (blank). 2N2 is used for amount of N2 evolved in order to directly compare the mass balance with NO3-.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

Fig1: Comparison of nitrate utilization and nitrogen gas evolved with and without super plasticizer as an electron donor in 1.0 mmol/dm3of nitrate solutions and 1000 mg/dm3of activated sludge as the microorganism. Run 2 was carried out with the electron donor and Run1 was carried out without the electron donor (blank). 2N2 is used for amount of N2 evolved in order to directly compare the mass balance with NO3-.Lines are shown to help identify the general trends shown by the data.
Mentions: In series A, Run 1 was run as a blank and Run 2 contained super plasticizer in order to elucidate the potential of super plasticizer as an electron donor on the behavior of NO3– reduction using activated sludge as the microorganism. The temporal changes in the composition of nitrogen compounds in Run 1 and Run 2 are shown in Figure 1. Although NO3– was consumed in the blank test (Run 1), more NO3– was reduced to produce more N2 by the presence of super plasticizers (Run 2). The consumption of NO3– in the blank test will be discussed in more detail later. The material balance of nitrogen classified according to species (NO3–, NO2–, NH3, N2 or solid phase [Nsolid]) is shown in Figure 2. Nsolid was calculated from nitrogen contents of the solid fraction. In the Figure 2, 2N2 was used for direct comparison in atomic nitrogen base. In Run 2, NO3– initially accounted for all nitrogen not in the solid phase. The production of NH3 and the appearance of NO2– was limited to the first 6 days of reaction. Consequently, the NO3– decrease could be broadly correlated with the production of N2.Figure 1

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