| The farmland soil contaminated by polycyclic aromatic hydrocarbons (PAHs) is gradually emerging and becoming increasingly serious in some areas of China with the rapid development of economy. PAHs are a group of chemicals with several fused aromatic rings, which have shown high environmental risks due to the severe toxicity of low molecular weight PAHs (<4rings) and the strong carcinogenic, teratogenic, mutagenic potential of high molecular weight PAHs (≥4rings). PAHs accumulate in soils and sediments diffusely, and disserve farm produce security and human health. This has caused increasing environmentists’concerns. In this thesis, an enhanced remediation with microbial-biosurfactant addition and stirring on dissipation of PAHs contaminated soils were conducted, and the combined effects of PAHs-specific degrading bacteria, mycorrhizal fungi and rhamnolipid on phytoremediation of long-term PAHs contaminated arable soils with alfalfa were investigated. As well as the pot experiments in greenhouse were carried out to investigate effects of application organic waste on the effect of PAHs-specific degrading bacteria on phytoremediation of arable soils that had long been contaminated by PAHs. The main results were as follows:(1) The pot experiments in greenhouse were carried out to investigate effects of PAHs-specific degrading bacteria (DB) inoculation and biosurfactant-rhamnolipid (RH) complement on the remediation of long-term PAHs contaminated soils. Results indicated that DB inoculation and RH complement significantly increased total PAHs and promoted degradation of PAHs different in number of rings in the soil. After90days of incubation, the PAHs degradation ratio of Treatments RH, DB and RH+DB reached to21.3%,32.6%and36.0%, respectively, and increased by333.0%,563.3%and633.0%as compared with that (4.9%) of the control. The PAHs-specific degrading bacteria inoculation promoted the degradation of high-molecular-weight PAHs more than that of low-molecular-weight PAHs. In addition, the average PAHs degradation ratio declined with the number of rings of the15PAHs. It was also found that the number of PAHs degrading bacteria, dehydrogenase activity and polyphenol oxidase activity in soils of Treatments DB and RH+DB were much higher than in Treatment RH and in CK, but differed slightly between Treatment RH and CK, suggesting that the mechanism of DB promoting degradation of PAHs in the soil was different from that of RH.(2) The pot experiments in greenhouse were conducted to study the combined effects of PAHs-specific degrading bacteria, mycorrhizal fungi (Glomus caledonium L) and rhamnolipid on phytoremediation of long-term PAHs contaminated soils using alfalfa (Medicago sativa L.). The results indicated that:the effect of single inoculation of PAHs-degrading bacteria (47.9%) was better than that of single inoculation mycorrhizal fungi (46.4%) and the effect of single complement of rhamnolipid (30.0%). The effect of double factors combined significantly improved the degradation ratio of PAHs, in which the synergy effect of PAHs-degrading bacteria and mycorrhizal fungi inoculation was better. The PAHs degration ratio was the highest with alfalfa growth after inoculation of PAHs-specific degrading bacteria, mycorrhizal fungi and complement of rhamnolipid (66.7%), showing the effect of enhanced rhizosphere bio-synergistic. In addition, the average PAHs degradation gradually reduced with the increase of the PAHs rings. But microorganism inoculation and rhamnolipid complement promoted the degradation of high-molecular-weight PAHs more than that of low-molecular-weight PAHs. The number of PAHs degrading bacteria, dehydrogenase activity, polyphenol oxidase activity and the removal ratio of PAHs showed positive correlation. Therefore microorganism inoculation and rhamnolipid complement were effective in enhancing the phytoremediation efficiency of the long-term PAHs contaminated soils.(3) The pot experiments in greenhouse were carried out to investigate the effect of addition cow dung from anaerobic fermentation and dry powdered sludge of papermaking black liquid on the effect of PAHs-specific degrading bacteria on phytoremediation of arable soils that had long been contaminated by PAHs. Results indicated that organic wastes addition and PAHs-specific degrading bacteria inoculation promoted alfalfa growth and PAHs degradation in the soil, especially in adding low content organic wastes. After60days, soil PAHs concentration reduced25.8%,34.9%,32.0%,43.7%,27.7%and21.9%for the treatment of PAHs-specific degrading bacteria inoculation, cow dung from anaerobic fermentation (low, high content) and dry powdered sludge of papermaking black liquid (low, middle, high content) addition, respectively, but only5.6%for control. In addition, the average PAHs degradation gradually reduced with the increase of the PAHs rings. But PAHs-specific degrading bacteria inoculation and organic wastes addition promoted the degradation of high-molecular-weight PAHs more than that of low-molecular-weight PAHs. The number of PAHs degrading bacteria and dehydrogenase activity and the removal ratio of PAHs showed significant positive correlation. |
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