The employment of bioadsorptive carriers possesses some advantages compared to the conventional soil washing technology with respect to ecological as well as economic aspects.
During the conventional soil washing process, up to 20 % of the soil (the small-sized particle fraction) has to be disposed as a highly contaminated hazardous waste. The accumulation of the pollutants to the small-sized particle fraction can be prevented to a largeextent by the addition of bioadsorptive carriers during the soil washing procedure. This way the only low-contaminated small-sized particle fraction can be added to the washed soil at the end of the treatment. The generated product is thus very similar to the natural soil structure. Furthermore, the proposed procedure opens the possibility to treat soils with high small-sized particle shares also. The limits of the process must, however, be determined in further investigations.
Since a portion of the microorganisms introduced into the soil during treatment remained in the cleaned soil, a complete decontamination during the soil washing process was not required in most cases. The elimination of the remaining pollutants occurred during a following microbial degradation period within the soil.
The microorganisms used can be optimized for a given purpose by immobilization at a suitable support and by cultivation in the soil washing waterused or in synthetic sewage.
During the regeneration, the loaded carriers and the water from the washing process were decontaminated and could be reused. In some cases the addition of nutrients, such as ammonia or phosphate, was necessary. So, considerable amounts of the water from the soil washing process, which is cleaned up presently with costly combinations of different procedures, could be recycled. First attempts to the biotechnological treatment of phenol-containing water were implemented successfully at the plant of the RST Recycling Sanierung Thale.
Since the biological regeneration of the carriers and the washing water is relatively inexpensive, the proposed procedure can contribute to a significant reduction of the expenditures compared to the conventional process. With respect to the carrier prices, for soils containing 20 % smallsized particles a cost-neutral use of the proposed method is given for prices below 100 DM/t carrier. According to our findings, the carriers could be reused up to 10 times. So it would be possible to use also more expensive specialized products, which can be adapted to the respective purpose.