Biosurfactant And Its Application In Lead Contaminated Sediment Remediation

With the development of industry, a mass of heavy metals are released into sediment. Contamination in sediment can endanger the growth of aquatic organism, and then harm land species and humans through bioconcentration and food chain amplifying function. It is promising to remove heavy metal from sediment because of its toxicity. In recent years, remediation methods to heavy metals were widely studied. There are three main methods to remediate heavy metal pollution, including physical method, chemical method and bioremediation method. The disadvantage of physical method is consumable, and physical method can't remove heavy metals to background value. Chemical method can induce secondary pollution. So physical method and chemical method are not ideal remediation to heavy metals. Biosurfactants are amphiphilic molecules with both hydrophilic and hydrophobic portions which are produced by microorganism. Biosurfactant applications in environmental industries are promising due to their biodegradability, low toxicity and effectiveness in enhancing the biodegradation and solubilization of low solubility compounds.Summarization of the thesis introduced the situation of heavy metal pollution in sediment, main removal heavy metal methods and the applications of biosurfactant. In this study, bacteria B-1 isolated from oily-waste water is object of this study. The best fermentation condition was determined by one-variable-at-a-time method, and obtained large yield biosurfactant at that condition. Biosurfactant was extracted and analysed its structure by thin layer chromatography and Fourier transform infrared. The result suggested that biosurfactant produced by bacteria B-1 was glycolipid. At last, Pb removal efficiency by biosurfactant at difference conditions was tested. The conclusions are as follows:(1) Two strains were isolated from bacteria B-1, named Bbai-1 and Bru-1. Bbai-1 and Bru-1 were identified as Brevibacillus parabrevis and Pantoea agglomerans respectively by biochemical and physiological characteristics, morphological and 16S rDNA.(2) The study of B-1 fermentation determined the optimal substrate component was (in gram per liter of water): peanut oil 40 g/L; urea 5 g/L; K2HPO4 3 g/L; NaCl 5 g/L; pH 7.0. And the B-1 was cultured in a gyratory shaker at 150 r/min at 25℃.(3) A biosurfactant with a low critical micelle concentration, CMC (175 mg/L), was produced by B-1 strain. The yields of crude biosurfactant were 0.6-0.7 g. Measurements of surface tention showed a high level of tolerance to temperature, pH and salinity of the product.(4) Compared to synthesized surfactant SDS, biosurfactant removed heavy metal more effective. 14.6% lead could be removed by SDS solution, while biosurfatant can remove 25.3% lead at the concentration lower than SDS concentration. The concentration and pH of biosurfactant solution can influence removal efficiency of Pb at a large degree. Removal efficiency of Pb could be enhanced with the increase of the biosurfactant concentrations, and could finally reach 25.3%. The best remediation was got when the pH of biosurfactant was 9, and 50.7% lead was removed at the condition. The ionic strength had a slightly influence on the removal of lead. Removal efficiency of Pb increased to 46.6% when adding 10 mmol/L NaNO3 to biosurfacment solution. With increasing the concentration of NaNO3, the effect of Pb removal decreased. With increasing washing time and times, removal efficiency of Pb was improved. Considering application economy, 60 h was determined as the optimal washing time. Lead in inartificial polluted sediment was more difficult to remove than it in artifical polluted sediment by biosurfactant. Comparing the spices transformation of lead before and after remediation in the sediment by Tessier method, it was evident that soluble species, carbonated fractions and iron-manganese oxides bound of Pb adsorb on the sediment were wiped off effectively.(5) Fourier transform infrared illustrated that biosurfactants change sediment surface properties, and cause heavy metals desorption from sediment.