Bioremediation Of Saline Soil Contaminated With Petroleum

Petroleum contamination, which has significantly threatened human health and ecosystem security, is an important environmental problem that should be solved quickly. In China, the soils of many oil production bases are various degree of salinity. The saline soil is easy to be contaminated when the petroleum is exploited, processed and utilized, finally turned into petroleum contaminated saline soil. Bioremediation is an effective, economic and environmental way to eliminate petroleum contaminated saline soil. There are many studies reported the bioremediation of petroleum contaminated soil, but the bioremediation of petroleum contaminated saline soil, which has received less attention in the literature, is an important environmental task that should be solved quickly. In this study, one efficient halotolerant petroleum-degrading bacteria (BM38) and an high-efficient biosurfactant-producing bacteria (BF40) were screened from the long term petroleum contaminated saline soil samples in Yellow River Delta. A series of liquid incubation experiments were conducted to researched the halotolerance, producing biosurfactants and characteristics of petroleum-degradating of BM38, discussed the effect of different factors to the biosurfactant and dynamics of a salt-tolerant Serratia BF40, analyzed and identified the product of BF40based on the morphological, physiochemical characteristics. Laboratory simulation test of petroleum contaminated soil remediation were also studied to discuss the effects of BM38, BF40and their products to the petroleum degradation in saline soil, the effects of different soil conditions to the accelerating of saline soil remediation by BM38and BF40inoculating and biosurfactant application. A halophyte that was suitable for petroleum contaminated soil remediation was screened by seed germination experiments and plant remediation texts. A phyto-microbial remediation system in petroleum contaminated saline soil was structured. The results will provide support for the bioremediation of petroleum contaminated saline soil. The main result of the study could be seen as below:1.54bacteria strains were isolated from the petroleum contaminated saline soil samples in Yellow River Delta, One bacterium (strain BM38) were found to efficiently degrade crude oil in highly saline environments based on a series of liquid and soil incubation experiments. According to its morphology, physiochemical characteristics and16S rDN A sequence analysis, this strain was identified as Pseudomonas putida. The salt resistant test demonstrated that strain BM38grew well at NaCl concentrations ranging from0.5%to6.0%. Strain BM38could produce a bioemulsifier in a liquid culture medium. The highest emulsifying capacity of fermentation broth comes out in the steady growth stage. But NaCl concentration had the significant effect on the emulsifying capacity of fermentation broth. This strain was able to grow in mineral liquid media amended with hexadecane, toluene, phenanthrene, isooctane and cyclohexane as the sole carbon sources. Among these hydracarbons, strain BM38showed the higher ability to degrade n-alkanes and aromatic hydracarbons. The crude oil degradation curve of BM38conforms to the first-order reaction kinetic model in the medium containing1%,3%and5%NaCl. The neutral and alkaline environments are suitable for degradating of BM38to crude oil. The degradating rate was higher at NaCl concentrations ranging from0%to3%. The temperature, concentration of crude oil and the inoculation amounts have significant effects to the degradating capacity of BM38.2.41microbial strains were isolated from saline soil contaminated by crude oil of the Yellow River Delta through plate culture method, using crude oil as C and energy source. BF40strain with salt-tolerant ability was screeded in this study, based on culture solution of degreasing, biosurfacial and emulsifying activities from different strains. Surface tension of BF40culture solution reduced to28.4mN·m-1, and emulsifying index was96.8%. BF40strain was identified as Serratia sp. It can grow in the saline condition ranged from0.5～7%of NaCl, and its salt-tolerant ability reached moderate level. After incubation of7d,56.7%of crude oil in BF40liquid culture with1.0%of NaCl was degraded. Biosurfactant production of BF40was affected by the forms of C and N sources. The greatest production was observed in the treatment using beef extract as C source and NH4Cl as N source. The higher production also founded in neutral or weak alkaline condition under temperature ranged from30to37℃. Biosurfacial activity of BF40was affected by salinity obviously. The lower effect of salinity on biosurfacial activity was founded than that on emulsifying activity. Biosurfacial activity of BF40was proposed to be the model of grow correlated. Biosurfactant (BS40) from BF40was determined to be lipopeptides by thin layer chromatography and GC-MS analysis. The critical micelle concentration of BS40solution was32.8mg·L-1. BS40possessed high temperature, salt, and acid-base tolerant properties. Higher emulsifying activity also observed for p-xylene, diesel, liquid paraffin and olive oil.3. Results of soil remediation experiment showed that biosurfactant (BS38) from BM38increased crude oil biodegradation insignificantly. Inoculation with exogenous strains (BF40, BM38, and BM38+BF40) or biosurfactant of BS40can increase crude oil degradation, and the greatest degradation rate was founded in the treatment with BS40addition and BM38inoculation, showing48.3%of degradation rate after60d incubation. Combination of BS40addition and BM38inoculation can effectively enhance saturated and aromatic hydrocarbon and asphalt degradation through GC analysis, and n-alkanes was almost degraded completely. The improvement of pristine and phytane degradation was also significant. Different effects on surface tension of soil solution and soil dehydrogenase activity were observed among exogenous strain inoculation, BS40addition, and BS38addition, which indicated that exogenous strain inoculation and biosurfactant addition improve soil remediation through different mechanisms.4. High salinity inhibited crude oil degradation in soil. Combination of BM38seeding and BS40addition can increase crude oil degradation in soils with different salinity. In weak alkaline soil, the greater crude oil dissipation was in the treatment with combination of BM38seeding and BS40addition. In the soil contaminated with high and moderate levels of crude oil, combination of BM38seeding and BS40addition can significantly increase crude oil degradation rate. Corncob addition increased crude oil degradation better than that did by cottonseed hull, wheat bran and cornstalk addition.5. Phytoremediation experiment showed that Alopecurus pratensis Swartz. possessed high crude oil tolerant ability, biomass, and the greatest remediation efficiency. In plant-microbial systems, Alopecurus pratensis Swartz. cultivation in combination of BM38seeding and BS40and corncob addition treatment, significantly increased population of total heterotrophic bacteria and crude oil degrading bacteria, which in turn enhance degradation. In combined remediation system, saturated and aromatic hydrocarbon degradation was mainly caused by BM38seeding and BS40addition, and gelatine degradation was mainly caused by Alopecurus pratensis Swartz. cultivation. Soil dehydrogenase activity positively correlated with microbial population. Combination of BM38seeding and BS40addition increased soil dehydrogenase activity insignificantly, while Alopecurus pratensis Swartz. cultivation increased significantly.