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English Summary

Biological decomposition of polyaromatic hydrocarbones (PAH) is a big problem in the established soil treatment plants because of their resistance to bacterial decomposition. This circumstance implies that a high content of PAH results in high retention times at the soil treatment plants or that the soil has to be retreated by thermal decomposition, extraction or to be deposited. Since large amounts of polluted soil are handled in Denmark - in 1993 app. 300,000 tons - there is a very good reason for examining the possibilities of optimizing the biological decomposition of PAH. Good results with decomposing PAH by means of whiterot-forming fungi have been obtained on a laboratory scale. These fungi release enzymes which decompose lignin in wood, the natural environment of the fungi. Lignin is a collection of very complex substances, and the enzymes, which decompose them, are also relatively unspecific, resulting in their capability to decompose PAH. In this project an examination of whether the promising results, which have been obtained in laboratories with decomposition of PAH from whiterot-forming fungi, can be applied to the biological soil treatment plants and of which changes may be caused in the PAH decomposition rates, was carried out. The project has included examination of the reproduction possibilities of potential PAH decomposing fungi to a large scale, inoculation of PAH polluted soil with PAH decomposing fungi/straw at A/S Bioteknisk Jordrens, Kalundborg, and examination of the influence of the fungi on the PAH decomposition in the inoculated soil miles and control miles without fungus. These examinations showed that it is very difficult to apply the results from the laboratory on a large scale. It turned out to be very difficult to obtain sufficient growth of most whiterot-forming fungi on straw, partly because they grow relatively slowly, and partly because on this scale there will unavoidable be growth of mould fungi in the straw which will lead to further reduction of growth of the whiterot-forming fungi. Furthermore the examinations have shown that the distribution of PAH in the actual miles is extremely heterogeneous. This means that in experiments running from August 1996 to November 1997 we have not been able to see significant changes in the PAH contents in the miles inoculated with fungus and straw. Neither in the control miles without fungus/straw or in the miles with uninfected straw significant changes in the PAH contents could be found. The sampling has been made app. every 6 weeks with A/S Bioteknisk Jordrens standard methods with cutting out of 5 samples in a depth of one metre with subsequent pooling. The samples were analysed for PAH using the GC/FID method at A/S Bioteknisk Jordrens. The conclusion is: 1) Development of methods for more sure reproduction of potential PAH decomposing fungi to large scale is necessary 2) Examination of growth of potential PAH decomposing fungi in soil on various materials, and 3) Examination of actual PAH decomposition in authentic situations and of where the PAH pollution is more regularly distributed in the soil miles than they were in this project.

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