In the wake of the enforcement of the Soil Contamination Countermeasures Law of 2003, purification projects concerning soil and groundwater contaminated by hazardous pollutants are in the market, and various contaminated soil purification technologies have been developed. The technology to remediate soil to the original condition by purifying contaminated soil using biological functions is called bioremediation.
Bioremediation is generally an inexpensive and energy saving technology, compared to the physico-chemical remediation technologies such as solidification of soil and washing, incineration and disposal, bubbling of pumped groundwater for evaporation and adsorption and/or chemical oxidation of pollutants in groundwater. Bioremediation has been closely watched as an advantageous choice because it is very safe except in special cases. The technology has a benefit which minimizes the damage to soil and groundwater. However, bioremediation can not be applied to highly toxic substances. It has a limitation on the applicable range of contamination, such as slow purification. In addition, it is difficult to control because its process is scientifically complicated. Consequently, it sometimes did not produce the desired effect and required substantial time to be considered as a practical technology. Although bioremediation technology has now been in use for several years, other technologies with various characteristics went beyond basic studies and are now practical technologies. Also, looking forward to practical application in the near future, research of new technology is being done in the laboratory and the field. It can be said that this field is still attractive for the development of new technology.
Bioremediation is divided roughly into an in situ remediation method and an ex situ remediation method, depending on whether contaminants are purified in situ ground or not. Moreover, from the derivation of microorganisms, which is a purification agency, it is divided into biostimulation which activates indigenous microorganisms in contaminated sites and bioaugmentation which introduces exogenous microorganisms isolated and cultivated in the laboratory. A more economical technique has arisen from biostimulation, and it is known in the U.S. as natural attenuation, a process that waits for soil to recover while monitoring the self-purification capability of nature. Furthermore, if plants are used as a purification agency instead of microorganisms, it is called phytoremediation. Bioremediation is a technology with various options such as sites of purification, types of biological catalysts and methods. To understand it, users should know about research and development as well as project cases.
In the latest technical development in Japan, it seems that the following bipolarization of bioremediation techniques is occurring, one of which tends toward the need for higher economical efficiency. The other tends toward faster remediation rates than physico-chemical methodologies. Specifically, the former direction of remediation divergence is bioremediation using anaerobic processes which do not use electron acceptors, enhanced natural attenuation with little ingenuity, and phytoremediation which utilizes plants’ absolute economic efficiency. The latter divergence is high-rate bioaugmentation using chemical catalysts such as microbes with high clean-up capability, eyeing the possibility of the use of genetically engineered microorganisms and hybrid-type remediation which combines biological and physico-chemical methodologies. These are the fields in which Europe and the United States used to be ahead. It can be said that unique technologies are now being developed which goes with Japan’s climate, landscape and social circumstances.
In this series, some of the first-line engineers of the companies which are taking part in environmental remediation projects will introduce various kinds of bioremediation technologies and describe the future prospects, respectively. This series will lead the reader to understand the present state of practical bioremediation technologies and the direction of future technical development.