Features
1 Remediation technologies applied to contaminated sites in Japan
Tatemasa HIRATA
Department of Environmental Systems,
Faculty of Systems Engineering,
Wakayama University

1. Classification of remediation for contaminated soil
The contamination of soil and groundwater is said to be accumulating incessantly. Unless the contaminants are completely degraded or removed in situ, the pollution state is not solved. As measures for the remediation of soil contamination, various technologies are currently being developed and applied in practical use, including the investigation technique. However, the procedures need more time and bigger budget. Conversely, soil and groundwater remediation has already been materialized as a form of business in Europe and America. As estimated based on the results of the investigation technique and from the remediation records in Japan, it is likely to cost trillions to 10 trillions yen on the market scale.
Innovative remediation technology has been developed centering on the superfund sites, especially in the U.S. The pioneering technology has been introduced to Japan and the technology suitable for local scenario and social economic situation of the country has been developed. Recently, manuals and laws in relation to soil and groundwater contamination have been approved. Simultaneously, they boost the development of technology for the remediation of polluted soil and groundwater.
The occurrence of soil and groundwater pollution varies and depends greatly on the process of soil formation or by different areas. The contaminants follow the course of water movement, which is dependent on the geology or the particular chemical properties of the substances. Therefore, an absolute remediation technology does not exist. Furthermore, a single technology is not enough to treat the same polluted spot from the early to the final stages.
Under such circumstance, the countermeasure technology, which has been utilized for the soil and groundwater contaminated places in Japan, can be classified in general into five elemental technologies shown in Fig. 1. The technology shown in Category A confines contaminants in situ or stabilizes them using certain medication. Although it prevents contaminants from diffusing into water, they remain in situ. Category B is the technology wherein contaminants are degraded chemically and biologically in situ. Meanwhile, Category C is the removal of contaminants in-situ by extracting the soil gas containing volatile contaminants and subsequently siphoning groundwater.
On the other hand, Category D is the technology in which contaminants is excavated and the 3 phases of soil, soil gas, and soil water are removed simultaneously. Even though this technology can be classified into the remediation technology like Category B or Category C, it is necessary to remove contaminants from the excavated soil or to detoxify the soil. The technology of treating contaminants extracted by these measures is classified under Category E. In like manner, various technologies are also developed according to the properties of the contaminants or the grade of contamination.Examples of such technologies are decomposition by solidification and stabilization, vitrification, thermal treatment, redox, and ex situ biotreatment.

Fig. 1 Classification of remediation technologies for contaminated soil and groundwater

Fig. 1 Classification of remediation technologies for
contaminated soil and groundwater

 

2. Development of economical and safe technology
The remediation of polluted soil and groundwater is highly expensive and the entire process takes a long time to complete. In order to advance a feasible project, disclosing information on the efficiency of the technology is needed for comparison with other technologies. The Ministry of Environment has released every actual proof concerning the remediation technology for the contaminated soil and groundwater space, efficiency and cost, specific effects to the environment, etc. The actual application of the procedures, including investigation technology, to the polluted areas has been disseminated, as well.
The implementation of remediation technology involving removal and detoxification of contaminants (B, C, D categories) is shown in Fig. 2. The result reveals that Category D, which combines excavation and treatment of polluted soil, occupies 63.6% of all the other categories.

Fig. 2 Remediation technology used in contaminated sites

Fig. 2 Remediation technology used in contaminated sites

 

The major technology involved in Category D is a blend of drilling contaminated soil and treatment processes, such as solidification and stabilization, vitrification, thermal treatment, redox, and ex situ biotreatment. The over-all process costs a lot but the purification is completed at a stretch and is highly effective. Moreover, due to the liquidation of real estate, the period of remediation using this remediation technology can be shortened.
In addition to such on-site needs, the implementation of the “Soil Contamination Countermeasures” law is uplifting the technical development of remediation technology, which is more economical and safer. As regards heavy metals as an example of pollutant, the technology which desorbs heavy metals using solvent, in-situ washing which delivers jets of water at super-high pressure into the contaminated soil, and vegetable purification using sunflower etc. are also tested.
On the other hand, volatile chlorinated organic compounds have been eliminated by means of air parsing technology, which has an installed Horizontal well and enlarged purification area, chemical and biological degradation in situ, chemical reduction decomposition technology using zerovalent iron, and incorporation of oxidizers like hydrogen peroxide or water-soluble organic matters into the groundwater as sources of electrons in order for a chemical reaction to occur.


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Present condition of soil pollution and the Soil Contamination Countermeasures Law
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2 Action to Remediation of Soil contamination(1)?Heavy metals