|２ Toward the era of commercializing bio-augmentatio|
Yoji Ishikawa, Hirokazu Tsuji, Kazuo Toge, Kensuke Fujii,
Yasushi Oda, Toshiaki Kimura
|Obayashi Corporation, |
Toyota Motor Corporation
Bio-augmentation implies bioremediation which introduces exogenous microbes cultivated in the laboratory. Bio-stimulation, on the other hand, activates indigenous microbes living in a remediation site by adding nutritional substance and oxygen
It is known that trichloroethylene (TCE) is degraded by aerobic co-metabolism. TCE is effectively degraded by microbes using chemical substances such as methane, phenol and toluene. The MO7 strain with a high TCE degrading ability was selected because using microbes with a high degrading ability for soil remediation is effective. The MO7 strain does not use gene recombination microbes, and is not genetically recombined, only isolated from nature (Fig. 1). Genetic lineage analysis of 16SrRNA indicates that the MO7 strain belongs taxonomically to Janibacter. It grows vigorously in the range of neutral pH under conditions between 20- 30°C. It is a phenol-using bacteria which can be cultivated by using nutrition or inorganic medium.
The safety in soil remediation technology using the MO7 strain and its microbes are identified in detail in “Recombinant DNA Technology Industrialization Guidelines”. The safety in pathogenicity and physiological property of the MO7 strain itself on humans and animals and plants is confirmed based on the data verified by non-toxicity tests shown in Table 1. The soil remediation technology specifically noted that there are no problems concerning safety in the introduction to work area, behavior in work area and every process after remediation. It has been confirmed that this soil remediation technology meets the guidelines. One of the characteristics of this soil remediation technology is the utilization of microbes. In the soil remediation technology, the microbes cultivated are harvested and washed. Next, resting cells remove phenol, an inducer of TCE- degrading enzymes, and are deposited into the soil. Therefore, harmful phenol itself is not deposited into the soil. Moreover, there is no secondary contamination caused by nutrient salt because there is no additional nutrient salt deposited into soil. There is a safety benefit: less possibility that microbes in the soil increase after remediation because nutrient salt is removed by washing. Also, postulated degradation pathways of this technology are shown in Fig. 2. The compounds such as dichloroacetic acid, trichloroacetic acid and chloral expected as an intermediate of trichloroethylene degradation, each of which was not detected.
Fig.２ Postulated Degradation Pathways of Trichloroethylene by MO7 Strain
Fig.３ Schematic Flow of the Degradation Method utilizing MO7 Strain
Bio-augmentation using safety-confirmed microbes degrades harmful substances into harmless residue. Additionally, the technology is low cost and has no secondary contamination, and the organization of administrative guidelines also supports it. The future development of bio-augmentation is expected to be not only a technology with low environmental impacts but also a profitable business method.