Study On Enhanced Bioremediation Effects And Biotoxicity Variation Of Petroleum-contaminated Soil

Due to a lot of exploitation of oil resources,ground crude oil has deteriorated the quality and safety of soil and groundwater,and the pollution has becoming increasingly serious.At present,the measures to repair contaminated soils mainly included physical methods,chemical methods and biological methods at home and abroad.Among them,the biological methods have becoming the most perspective soil remediation technology,which have the characteristics of environment friendly and low cost,and were quickly developed in domestic and oversea in last decade.Present studies were focused on adding the soil nutrients(such as N、P,et cetera)to improve the activity of indigenous microorganisms,which could achieve soil bioremediation,but this method could not achieve the best results.In this paper,degrading bacteria which possessed strong acclimatization and could degrade the oil quickly were added to the petroleum polluted soil,and the specified plant(Lolium perenne L.)was cultivated into the soil.The plant-microbial combined remediation could improve the bioremediation efficiency of the contaminated soils,which could provide theoretical basis for the engineering practice.The main results of this study are summarized as follows:1.Three strains of microorganisms that could degrade oil were isolated from the oil contaminated soil,the garage sludge and active sludge of sewage plants.According to the molecular biology identification,the three isolates were: Chryseomicrobium sp.,YL2,Gordonia sp.YL3,and Acinetobacter sp.YL5.2.The oil degradation characteristics of the three strains were studied.The results are as follows.Gordonia sp.YL3 could only degrade oil effectively under low oil concentration(3 g/L),and it’s total petroleum hydrocarbons(TPH)degradation ratio could reach 57.83% under the condition of inoculation amount 10% and the temperature 30 ℃;Chryseomicrobium sp.YL2 had high degradation ratio of 75.27% under the condition of initial oil concentration 6 g/L,inoculation amount 10% and 30 ℃.With the higher inoculation amount of the strain,the TPH degradation ratio of the strain would be higher,and the time required for the degradation would be shorter.Compared with the 6% inoculation amount,the 10% inoculated amount could achieve the same result about two days in advance;The oil degradation characteristics of Acinetobacter sp.YL5 were best among them.And the TPH degradation ratio of the strain was as high as 84.60% under the condition of initial oil concentration 6 g/L,inoculation amount 10% and 30 ℃;Acinetobacter sp.YL5 and Chryseomicrobium sp.YL2 were mixed together by the ratio of 1:1.And the TPH degradation ratio of the mixed strain could reach 84.56%.At the same time,the TPH degradation ratio of single strain were 76.32%,83.26% respectively,which illustrated that the degradation effect of the mixed strain had no significant improvement.3.Acinetobacter sp.YL5 and the mixed strain were added to the petroleum-contaminated soil.The results showed that the TPH degradation ratio of the mixed strain was better than that of the single strain.The final degradation ratio of the mixed strain was 1.16 times of that of the single strain.The use of the mixed strains could maintain a high level of microbial biomass in the soil,which could contribute to the degradation of the oil.The single stain and the mixed strain had higher dehydrogenase activity of 547.49 μg/(g·d)and 623.86 μg/(g·d)respectively at 28 d,which were significantly higher than that of the control group(110.16 μg/(g·d)).4.The plant-microbial enhanced bioremediation experiments were conducted by adding the mixed strain to soil or planting perennial ryegrass in the soil.The results indicated that in the bioremediation process of plant-microbe combination,the highest degradation ratio of TPH reached 53.08% after 150 d,1.60 times higher than that in the blank group,and the dehydrogenase activity reached 521.80 μg/(g·d),which was 8.12 times higher than that of the blank group,which means in the process of restoration,microbes played a major role.The biotoxicity of oil contaminated soil was significantly reduced by enhanced bioremediation,and the TEQphenol was reduced from the initial value of 1633.21 mg/L to 171.08 mg/L.Plant-microbial remediation method could repair oil-contaminated soil efficiently and had good removal on the toxic substances in soil.