Isolation Of N-hexadecane Degrading Bacteria From Petroleum Contaminated Soil And QE And Its Degradation Capability Study

The oil industry has been developing rapidly after the Industrial Revolution.It was estimated that about 800,000 tons of hydrocarbons enter the environment with large amouts of hydrocarbons extraction.Most of these oil pollutants remained in the soil environment,decreasing the soil permeability,and causing serious damage to natural ecosystems.Among them,n-hexadecane is an important component of alkanes,which are the most abundant in hydrocarbons.It is a persistent pollutant in the environment because of its hydrophobic character and low water solubility,which makes it even more difficult to degrade.Microbiological remediation of hydrocarbons in polluted environments is claimed to represent an efficient,economic and versatile alternative to physicochemical treatment.In this study,the highly efficient n-hexadecane degrading strains were screened and isolated from the petroleum contaminated soil of Dongying,Shandong Province of China and QE(a new environmental-remediation agent)as well;and the n-hexadecane degrading strains were further optimized by orthogonal experiment and then they were applied in the laboratory soil bioremediation experiments.These investigations could provide some theoretical basis for microbiological remediation of petroleum.Two highly efficient n-hexadecane degrading strains,named TZSX2 and QZSX8,were isolated through enrichment in a Bushnel-Hass medium,with n-hexadecane as the sole source of carbon and energy after 50d from the petroleum contaminated soil of Dongying and QE.The strain TZSX2 and QZSX8 were identified as Rhodococcus and Bacillus,respectively,based on the study of morphological observation,physiological and biochemical identification,and molecular biology identifications.For the strain TZSX2,the optimal conditions for degradation were 2%inoculum size,5g/L NaCl concentration,9 in pH at 36?when the initial n-hexadecane concentration was 10mL/L.It would allow the highest growth rate and the greatest degradation rate of 91%under the optimal pH of 9.Above all,the screened strain TZSX2 showed high capabilities of alkali tolerance with excellent degradation efficiency for even high concentration of n-hexadecane,and thus it would be quite suitable for the remediation of petroleum contaminated soil especially in the extreme environment.For the strain QZSX8,with the same orthogonal experiment,the optimal conditions for degradation were 4%inoculum size,0.5mL/L initial n-hexadecane concentration,40g/L NaCl concentration,8 in pH at 36?.And under the optimal temperature of 36?,the greatest degradation rate of 100%could be obtained with the initial n-hexadecane concentration from 0.2 to 1.5mL/L.Bioaugmentation was applied to remediate 10 mL/L n-hexadecane-contaminated soil which was collected from Dongying,Shandong Province of China.In order to make the amount of n-hexadecane-degrading bacteria in the soil up to 10~7CFU/g,20mL TZSX2 bacteria solution was added to sterile and non-sterile soils separately.The degradation rates of n-hexadecane in the non-sterile soil treatment on the days of 10th,20th,30th was 28.0%,38.4%and 51.0%respectively.Compared with the sterile soil treatment,it was increased by 16.2%,8.1%and 8.2%,respectively.It indicated that the strain TZSX2 could degrade the n-hexadecane in the soil effectively,and coexist well with the indigenous bacteria in the soil.Moreover,20mL TZSX2 bacteria solution and 20mL TZSX2and QZSX8 mixed bacteria solution was added to non-sterile soils,respectively,with the same n-hexadecane-degrading bacteria of 10~7CFU/g.The results showed that both treatments can increase the amount of soil microorganism significantly.The degradation rates of n-hexadecane in treatment adding both TZSX2and QZSX8 bacteria achieved 35.0%,49.8%and 61.0%on the days of 10th,20th,30th,respectively.It was increased by 7.0%,11.4%and 10%,respectively,compared with the treatment with only TZSX2.This study will provide technical ideas for oil-polluted environmental remediation problems.It could also promote the popularization and application of the screening bacteria agents and QE powder effectively in the bioremediation of petroleum contaminated soil.