Production Of Biosurfactant Rhamnolipid And Its Application In Remediation Of Polychlorinated Biphenyl Contaminated Soil

Polychlorinated biphenyls are important environmental organic pollutants due totheir carcinogenicity. They are physically and chemically stable, and resistant todegradation. Their strongly hydrophobic nature make them bind to soil tightly,resulting in remediation of PCBs contaminated soils a challenge problem.Bioremediation has performed a great promise as a potentially effective and low-costtreatment option of hydrocarbon contamination However, the low bioavailability ofPCBs leads to their slow biodegradation. An option to enhance the bioavailability ofhydrocarbons is to add surfactants. Surfactants could increase the aqueousconcentration of hydrophobic compounds resulting in higher mass transfer rate andbioavailability. But the use of synthetic surfactants in biotreatment processes has beenrather limited due to their toxicity and non-biodegradation. Biosurfactants have theadvantages of being readily biodegradable and non-toxic compared to chemicallyproduced surfactants which makes them more valuable in hydrocarbon biodegradation.In this study, biosurfactant production and its application in remediation ofpolychlorinated biphenyl contaminated soil were investigated. The main results weresummarized as follows:(1) The optimal medium components and growth conditions for rhamnolipidproduction by the strain were studied using "Orthogonal experiment" method. Theresults showed that the optimal medium for rhamnolipid production by this strain was120g/L soybean oil,8.0 g/L NaNO₃, 1.0 g/L KH₂PO₄, 1.0 g/L Na₂HPO₄·12H₂O, 0.1 g/LMgSO₄·7H₂O,,0.2 g/L FeSO₄·7H₂O, pH 7.0. Under such conditions, the yield ofrhamnolipid was as high as 17.73g/L within 96 h.(2) High pressure liquid chromatography/mass spectrometry using electrosprayionization was first used to analyze the components of rhamnolipid biosurfactant.Groups of rhamnolipid homologs from the biosurfactant mixture produced by thestrain with soybean oil as carbon source were isolated and identified. The main typesof rhamnolipid were R1 and R2 with molecular weight 650 and 504, which in the nameof di-rhamnolipid and mono-rhamnolipid.(3) After purification, the critical micelle concentration of the Biosurfactan is 54mg/L.Its surface tention is 28.87mN/m. Highly surface activity abtained by therhamnolipid.(4) Biosurfactant rhamnolipids were used to study the effects on Polychlorinated Biphenyl (PCBs) desorption from contaminated soil. The results show that thedesorption of PCBs from contaminated soil is affected by the concentration ofrhamnolipids,the temperature,the ionic strength and the pH values of the soil .Rhamnolipids don't improve PCBs desorption from contaminated soil when theirconcentrations are below or near their critical micelle concentration (CMC) values.While, rhamnolipids could obviously enhance the desorption process when theconcentrations exceeded the CMC values. The desorbed amount of PCBs wereincreasing with the increase of rhamnolipids concentrations. But temperate had noefforts on PCBs. It was also found that the desorbed amount gradually increased withthe increase of pH values of the soil, which indicated that the high removal only tookplace in the alkaline environment. The ionic strength had a positive influence on thedesorption of PCBs.Through the research of adsorption PCBs from soil, we understandPCBs to affect the existence condition and rule of transformation. What's more, thebasic theory of PCBs soil repairprovides has been provided, and the significance to thepreventing of environmental pollution and the controlling of ecological environmentprotection were of vital importance.