Journal of Radioanalytical and Nuclear Chemistry

, Volume 297, Issue 1, pp 71–78

Remediation of soil/concrete contaminated with uranium and radium by biological method

Authors

    • Korea Atomic Energy Research Institute
  • Seung-Su Kim
    • Korea Atomic Energy Research Institute
  • Hye-Min Park
    • Korea Atomic Energy Research Institute
  • Won-Suk Kim
    • Korea Atomic Energy Research Institute
  • Uk-Ryang Park
    • Korea Atomic Energy Research Institute
  • Jei-Kwon Moon
    • Korea Atomic Energy Research Institute
Article

DOI: 10.1007/s10967-012-2321-x

Cite this article as:
Kim, G., Kim, S., Park, H. et al. J Radioanal Nucl Chem (2013) 297: 71. doi:10.1007/s10967-012-2321-x

Abstract

Biological method was studied for remediation of soil/concrete contaminated with uranium and radium. Optimum experiment conditions for mixing ratios of penatron and soil, and the pH of soil was obtained through several bioremediations with soil contaminated with uranium and radium. It was found that an optimum mixing ratio of penatron for bioremediation of uranium soil was 1 %. Also, the optimum pH condition for bioremediation of soil contaminated with uranium and radium was 7.5. The removal efficiencies of uranium and radium from higher concentration of soil were rather reduced in comparison with those from lower concentration of soil. Meanwhile, the removal of uranium and radium in concrete by bioremediation is possible but the removal rate from concrete was slower than that from soil. The removal efficiencies of uranium and radium from soil under injection of 1 % penatron at pH 7.5 for 120 days were 81.2 and 81.6 %, respectively, and the removal efficiencies of uranium and radium from concrete under the same condition were 63.0 and 45.2 %, respectively. Beyond 30 days, removal rates of uranium and radium from soil and concrete by bioremediation was very slow.

Keywords

BioremediationPenatronUraniumRadiumSoilConcrete

Introduction

Most nuclear facility sites have been contaminated by the leakage of radioactive waste-solution due to corrosion of the waste-solution tanks and connection pipes by their long-term operation set up the underground around nuclear facilities. For the reduction of radioactive waste volume, a method to remediate large volumes of radioactive soil needed to be developed. Up to now, soil washing methods have studied how to remediate soil contaminated with uranium, radium, cobalt, cesium, etc., [1, 2], but they have had low removal efficiency of nuclides from soils and they generates large volumes of waste-solution. Therefore, recently biological methods have been studied as an alternative new technology for soil remediation. The biological method can reduce the volume of waste-solution and the construction cost and operation cost of soil remediation equipment. The biological method uses microorganisms to reduce, eliminate, contain, or transform contaminants present in soils into benign products.

A number of studies have demonstrated the enzymatically catalyzed precipitation of insoluble phases of uranium by the microbial reduction process [36]. In addition to this reductive bioprecipitation process, insoluble mineral forms of radionuclides and metals can also be immobilized through interactions between microbially produced sulfide [7, 8] and phosphate [911] or through bacterial iron oxidation in a process termed biomineralization [12]. In contrast to microbial reductive precipitation, which requires anaerobic conditions, biomineralization can occur aerobically, making this process a possible remediation strategy for radionuclides in contaminated groundwater and oxygenated subsurface zones.

Analyses of the microbial community dominated within the groundwater also indicated a shift from a community dominated by organisms known to reduce sulfate, i.e., Desulfobacteraceae [13]. The results stress the importance of maintaining metal reduction within the subsurface or encouraging the growth and activity of sulfate-reducing bacteria capable of U(VI) reduction. Acetate-oxidizing sulfate-reduction bacteria have not been shown to reduce U(VI), although there is ample evidence that lactate-oxidizing sulfate-reducing bacteria are able to reduce U(IV) using lactate or hydrogen as electron donors [14, 15]. Thus addition of these electron donors to the sub-surface may stimulate U(VI) reduction in situ. Also, carbonate addition enhanced U solubilization, whereas pyrite addition essentially slowed the initial U solution [16].

In this study, penatron, that is an organic enzyme bacterial system, was mixed with soil contaminated with uranium/radium. Optimum conditions for mixing ratios of penatron and soil, and the pH of soil was determined through several bioremediation experiments with soil contaminated with uranium/radium. Also, under optimum experiment conditions, the removal efficiencies of soil and concrete according to lapsed time were measured for feasibility analysis of soil and concrete bioremediations.

Materials and methods

Laboratory tests and ex-situ bioremediation applications have shown that microorganisms can change the valence, or oxidation state, of radionuclides by using them as electron acceptors. In some cases, the solubility of the altered species decreases and the contaminant is immobilized in situ, e.g., precipitated into an insoluble salt in the sediment. In other cases, the opposite occurs-the solubility of the altered species increases, increasing the mobility of the contaminant and allowing it to more easily be flushed from the environment. Both of kinds of transformations present opportunities—either to lock them in place, or to accelerate their removal. Microorganisms can do much more than biotransform contaminants. They can also influence contaminant, or by altering the form of organic compounds that influence radionuclide and metal mobility (Fig. 1). A significant number of field studies and successful use of bioremediation strategies for radionuclides have occurred recently [17].
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Fig. 1

Three possible non-reducing mechanisms of bacterial influence on U(VI) geochemistry

Radioactive soil/concrete parameter measurement

The soils around a uranium conversion facility in Korea Atomic Energy Research Institute were sampled. Table 1 shows the soil hydraulic properties. Bulk density of the soil was 1.52 g/cm3, porosity was 41.4 %, and the hydraulic conductivity is 5.3 × 10−4 cm/s. And Table 2 shows the concrete hydraulic properties. Bulk density of the soil was 1.66 g/cm3, porosity was 39.5 %, and the hydraulic conductivity is 7.4 × 10−4 cm/s. Figure 2 shows the particle size distribution of the radioactive soil stored in a nuclear facility. An average particle size of the radioactive soil is 0.6 mm, which contains many minute particles. The main nuclide of the radioactive soil is uranium and radium, and this radioactive soil has been stored in 200 l drums in a storage facility. Figures 2 and 3 show the radioactivity concentration according to the soil/concrete particle size. Figure 4 shows radioactivity concentration according to the particle size. The smaller the size of the soil particle was, the higher its radioactivity concentration was.
Table 1

Hydraulic properties of soil contaminated with uranium around nuclear facilities

Parameter

Value

Bulk density (g/cm3)

1.52

Porosity (%)

41.4

Hydraulic conductivity (cm/s)

5.3 × 10−4

Water content (%)

27.5

pH

5.6

Table 2

Hydraulic properties of crushed concrete contaminated with uranium around nuclear facilities

Parameter

Value

Bulk density (g/cm3)

1.66

Porosity (%)

39.5

Hydraulic conductivity (cm/s)

7.4 × 10−4

pH

12.6

https://static-content.springer.com/image/art%3A10.1007%2Fs10967-012-2321-x/MediaObjects/10967_2012_2321_Fig2_HTML.gif
Fig. 2

Accumulated weight percent versus soil particle size

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Fig. 3

Accumulated weight percent versus concrete particle size

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Fig. 4

Radioactivity concentration according to the particle size

Bioremediation experiment

Four hundred grams of soil/concrete contaminated with uranium/radium was put in a 500 ml beaker. Several beaker samples were made to obtain optimum experimental conditions for bioremediation. The soil/concrete was mixed with penatron [manufactured by Maz-zee S.A. International (San Diego, CA)], i.e., organic enzyme bacterial system and anti-stress biological soil activators by aid to activate and to supply essential nutrients by activating microorganism metabolism. The components of penatron are spirostant (20 %). pargenin (15.62 %), sarsapogenin (15.53 %), sarsaponin (10 %), humic acid (10 %), so on. And then the mixed soil/concrete was put in an incubator for bioremediation at 25 °C as shown in Fig. 5. Twenty grams of soil/concrete was extracted from the beaker per 15–30 days, which was put on sieve of 0.075 mm and was washed with distilled water for removal of bacterial cells including uranium/radium from the soil and concrete. The washed soil/concrete was dried and its radioactive concentration was measured by multi-channel analyzer (MCA) as shown in Fig. 6. The removal efficiencies of uranium and radium from the soil/concrete were calculated by a ratio of concentration of the remediated soil/concrete versus concentration of the original soil/concrete, respectively. The original uranium/radium concentration was measured by MCA with a standard tube of 50 cc, QCY48 (Amersham), manufactured by KRISS (Korea Reach Institute Standards and Sciences). MCA operates in pulse height analyzer mode. The scintillation counter measures the pulse height distribution from a gamma ray source. The amplitude of an incoming analog pulse is digitized by analog digital converter (ADC) and the digital value is used as the address of a memory location that is incremented. Thus the screen display of number of counts versus channel number is really a histogram of the number of counts versus pulse height, i.e., a pulse height spectrum. The time required to measure the radioactivity concentration of a soil/concrete sample by MCA was estimated to be 5–10 h.
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Fig. 5

Incubator for bioremediation in constant temperature

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Fig. 6

Multi-channel analyzer (MCA) for radioactive concentration measurement

An optimum mixing ratio of penatron

To obtain an optimum mixing ratio of penatron, 100 g of distilled water was poured in three 500 ml beakers, respectively, and penatron was added in three beakers by 0.5 % (i.e., penatron: soil = 2 g: 400 g), 1 and 2 % as a weight ratio of penatron and soil, respectively. Next, the penatron solution in the beaker was mixed with 400 g of soil. The removal efficiencies of uranium/radium from different mixed soil were analyzed through three bioremediation experiments for 30 days, respectively.

The effect of bioremediation according to pH change

To obtain the optimum pH of the soil for bioremediation, the soil contaminated with uranium/radium in three beakers were adjusted to pH 6.0, 7.5, and 8.5 with NaOH and HNO3, respectively. The effect of bioremediation according to pH change was analyzed by measuring the removal efficiencies of uranium and radium from soil with pH 6.0, 7.5, and 8.5 according to lapsed time, respectively.

The effect of bioremediation according to change of initial uranium and radium concentrations of soil

The effect of bioremediation according to change of initial uranium and radium concentrations of soil was analyzed through several bioremediation experiments with different initial uranium and radium concentrations of soils.

Feasibility analysis of concrete bioremediation

For feasibility analysis of concrete bioremediations, bioremediation experiments for the removal of uranium and radium from concrete under optimum experiment conditions obtained through previous bioremediation experiments were carried out.

The removal efficiencies of uranium and radium from soil and concrete according to lapsed time

For feasibility analysis of soil and concrete bioremediations, the removal efficiencies of soil and concrete according to lapsed time were measured under an obtained optimum experiment conditions. The uranium and radium concentrations in soil were measured by MCA.

Results and discussion

To estimate the feasibility of bioremediation methods for soils contaminated with uranium and radium, several bioremediation experiments were carried out and the results are as follows:

An optimum mixing ratio of penatron

An optimum mixing ratio of penatron was obtained through bioremediation experiments for soil contaminated with uranium/radium. Figure 7 shows uranium concentration according to lapsed time under different injection ratio of penatron. On injection of 0.5 % penatron, the uranium in soil was removed by 45.8 % for 30 days. On injection of 1 % penatron, the uranium in soil was removed by 76.4 % for 30 days. And on injection of 2 % penatron, the uranium in soil was removed by 62.7 % for 30 days. That is, on injection of beyond 2 % penatron, the removal efficiency of uranium from soil was reduced. Therefore it was found that an optimum mixing ratio of penatron for bioremediation of uranium soil was 1 %.
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Fig. 7

Uranium concentration according to lapsed time under different injection ratio of penatron

Figure 8 shows radium concentration according to lapsed time under different injection ratio of penatron. On injection of 0.5 % penatron, the radium in soil was removed by 71.2 % for 30 days. On injection of 1 % penatron, the radium in soil was removed by 74.0 % for 30 days. And on injection of 2 % penatron, the radium in soil was removed by 73.9 % for 30 days. Therefore it was found that an optimum mixing ratio of penatron for bioremediation of radium soil was 1 %.
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Fig. 8

Radium concentration according to lapsed time under different injection ratio of penatron

The effect of bioremediation according to pH change

The optimum pH for soil contaminated with uranium and radium was obtained through several bioremediation experiments with different pH soils. Figure 9 shows uranium concentration according to lapsed time under different pH conditions. In the pH 6.0 soil, the uranium was removed by 77.0 % for 30 days. In the pH 7.5 soil, the uranium was removed by 79.2 % for 30 days. In the pH 8.5 soil, the uranium was removed by 66.0 % for 30 days. That is, in soil with the pH greater than 7.5, the removal efficiency of uranium from soil was reduced. Therefore it was found that the optimum pH condition for bioremediation of uranium soil was 7.5.
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Fig. 9

Uranium concentration according to lapsed time under different pH conditions

Figure 10 shows radium concentration according to lapsed time under different pH conditions. In the pH 6.0 soil, the radium was removed by 70.3 % for 30 days. In the pH 7.5 of soil, the radium in soil was removed by 73.2 % for 30 days. And in the pH 8.5 of soil, the radium in soil was removed by 67.8 % for 30 days. That is, in soil with the pH greater than 7.5, the removal efficiency of radium from soil was rather reduced. Therefore it was found that the optimum pH condition for bioremediation of radium soil was 7.5.
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Fig. 10

Radium concentration according to lapsed time under different pH conditions

The effect of bioremediation according to change of initial concentration of soil

The effect of bioremediation according to change of initial concentration of soil was analyzed through several bioremediation experiments with different uranium/concrete initial concentration of soils. Figure 11 shows uranium concentration according to lapsed time under different initial concentrations. With lower uranium concentrations, the uranium in soil was removed by 80.0 % for 30 days. With higher uranium concentrations, the uranium in soil was removed by 60.5 % for 30 days. That is, under higher uranium concentrations, the removal efficiency of uranium from soil was reduced. The reason was thought to be that bacterium in soil under higher uranium concentration died due to higher radioactivity. Figure 12 shows radium concentration according to lapsed time under different initial concentrations. With lower radium concentrations, the uranium in soil was removed by 73.2 % for 30 days. With higher radium concentration, the radium in soil was removed by 65.5 % for 30 days. Likewise, under higher radium concentrations, the removal efficiency of radium from soil was reduced.
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Fig. 11

Uranium concentration according to lapsed time under different initial concentrations

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Fig. 12

Radium concentration according to lapsed time under different initial concentrations

Feasibility analysis of concrete bioremediation

Bioremediation experiment for the removal of uranium and radium from concrete were carried out under injection of 1 % penatron at pH 7.5. Figure 13 shows uranium and radium radioactivity concentrations in concrete according to lapsed time during bioremediation. The uranium in concrete was removed by 58.2 % for 30 days and the radium in concrete was removed by 58.3 % for 30 days. Meanwhile, Fig. 14 shows a comparison of uranium removal efficiencies in concrete and soil according to lapsed time during bioremediation. The uranium in soil was removed by 79.2 % for 30 days, while the uranium in concrete was removed by 58.23 %. Therefore it was found that the removal of uranium and radium in concrete by bioremediation is possible but the removal rate from concrete was slower than that from soil. The reason was thought to be that the number of bacterium in concrete was smaller than that in soil due to high pH of concrete.
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Fig. 13

Uranium and radium radioactivity concentrations in concrete according to lapsed time during bioremediation

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Fig. 14

A comparison of uranium removal efficiencies in concrete and soil according to lapsed time during bioremediation

The removal efficiencies of uranium and radium from soil and concrete according to lapsed time

Bioremediation experiments for the removal of uranium and radium from concrete and soil were carried out under injection of 1 % penatron at pH 7.5. Figure 15 shows uranium and radium radioactivity concentrations in soil according to lapsed time for 120 days. The uranium in soil was removed by 81.2 % for 120 days and the radium was removed by 81.6 %. Figure 16 shows uranium and radium radioactivity concentrations in concrete according to lapsed time for 120 days. The uranium in concrete was removed by 63.0 % for 120 days and the radium was removed by 45.2 %. Beyond 30 days, removal rates of uranium and radium from soil and concrete by bioremediation was very slow. Therefore, future study to increase removal efficiency by bioremediation beyond 30 days is needed.
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Fig. 15

Uranium and radium radioactivity concentrations in soil according to lapsed time

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Fig. 16

Uranium and radium radioactivity concentrations in concrete according to lapsed time

Meanwhile, the upper result of uranium was compared with previous study results. Rafael et al. [18] investigated that maximum uptakes of uranium by three different bacteria communities were 92, 81, and 76 % from radioactive liquid organic waste for 20 days. The difference with the upper result, 81.2 %, is considered to be because uranium uptake from soil waste by bacteria community is slower and less than that from liquid waste. Also, Cem et al. [19] investigated that uptakes of uranium by bi-functionalized algae–yeast biosorbent were 85–90 % from aqueous solution. The difference is too considered to be due to different wastes, namely, soil waste and aqueous solution waste.

Conclusion

An optimum mixing ratio of penatron was obtained through three bioremediation experiments for soil contaminated with uranium and radium. For injections of greater than 2 % penatron, the removal efficiencies of uranium and radium from soil were rather reduced. Therefore, an optimum mixing ratio of penatron for bioremediation of uranium soil was 1 %. Also, it was found that the optimum pH condition for bioremediation of soil contaminated with uranium and radium was 7.5. The removal efficiencies of uranium and radium from higher concentrations of soil were rather reduced in comparison with those from lower concentrations of soil. Also, the removal of uranium and radium in concrete by bioremediation is possible but the removal rate from concrete was slower than that from soil. Finally, the removal efficiencies of uranium and radium from soil under injections of 1 % penatron at pH 7.5 for 120 days were 81.2, 81.6 %, respectively, and the removal efficiencies of uranium and radium from concrete under the same condition were 63.0, 45.2 %, respectively. Beyond 30 days, removal rates of uranium and radium from soil and concrete by bioremediation was very slow.

Acknowledgments

This work was supported by the Nuclear Research & Development Program of the Korea Science and Engineering Foundation (KOSEF) Grant funded by the South Korean Government (MEST).

Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2012