Oil Removal Efficiency And Mechanism Analysis Of High Effective Oil-degrading Bacteria Enhanced By Magnetic Field

In order to protect the marine environment,more and more stringent discharge standards were enacted by the International Maritime Organization(IMO)so that the traditional method of physical separation cannot meet the new requirement.More and more new oily sewage treatment technologies were developed and applied.Membrane Bio-Reactor(MBR)is a new sewage treatment technology that combines traditional biochemical process with membrane technique.As it has a compacted structure and high separation efficiency,it is very suitable for oily bilge wastewater treatment.Biological degradation plays an important role in the process of oily sewage treatment by MBR.Magnetic strengthening technology can improve the biological activity and promote the degradation of organic matter,therefore it has become a research focus in recent years.Oil removal efficiency and mechanism analysis of high effective oil-degrading bacteria enhanced by magnetic field were studied in this thesis.A strain of highly efficient petroleum-degrading bacteria was isolated which named B11,the impact of magnetic fields on its activity and biosurfactant were investigated to explore the mechanisms of magnetic fields' enhanced biodegradation.First of all,the growth and the oil removal efficiency of B11 were investigated under the magnetic field from 0m T to 60 m T.The highest oil removal efficiency reached 65.6% which is increased 8.1% and compared with the control groups when the magnetic field intensity is25 m T.The biomass was increased by 14.1% after magnetization in three days and the daily highest oil removal rate reached 32.6% on the second day.The biomass of continuous stimulation samples was 8.2% more than the one of the intermittent stimulation samples,and oil removal rate increased by 1.1%.The best magnetic field enhanced biodegradation efficiency was reached when the magnetic field intensity is 25 m T,the magnetization time more than three days and the stimulation is continuous.Secondly,the strengthening mechanism of the magnetic field was investigated by considering the growth,the cell surface morphology,the cell activity and the intracellular enzyme activity,the cell permeability and the protein,nucleic acid leakage situation of B11.The magnetic field can shorten the generation time in logarithmic phase and keep higher biomass which increased by 10.2% in the stable phase when the magnetic field intensity is25 m T.The morphology of cells was kept completely,the activity of cells and intracellularsuperoxide dismutase(SOD)were retained and increased by 25.2% and 12.3% in order to adapt the harsh environment.The permeability of cells and the extravasation of intracellular nucleic acid,protein content were kept properly in order to guarantee that cells can grow rapidly.It is observed that the activity of enzyme can be activated to promote the growth of B11 by magnetic field under the premise that the permeability of cells is kept properly.Thirdly,the oil removal efficiency was investigated by considering the hydrophobicity values oil spreading method,surface tension and the biosurfactant.Through blue gel test experiment,it was showed that the strains can produce surfactant material which can help the microbials uptake of the oil.The hydrophobic property of B11 was increased by 6.7% when the magnetic field intensity is 25 m T.The maximal oil displacement diameter reached 3.56 cm and the surface tension was 35.8m N/m.Through the analysis of thin-layer chromatography(TLC),it was observed that B11 can metabolize hydrocarbon to produce the surfactant which is glycolipid with the critical micelle concentration(CMC)of 67.7mg/L.But the activity of the surfactant cannot impact by magnetic field.There were 0.114 g per 100 ml surfactant that was extracted and increased 17.57% by comparing with the control group.The effect on the uptake of hydrocarbons by magnetic field can be enhanced through changing the strain of hydrophobic and enhancing the output of the surfactant.At last,the magnetic strengthening mechanism of the oil removal efficiency is investigated by the dehydrogenase activity of B11.The dehydrogenase activity reached 47.7TF?g/L·h-1,of which the extracellular dehydrogenase activity reached 30.1TF?g/L·h-1.The extracellular dehydrogenase activity was 70.05% higher than the intracellular dehydrogenase activity.It is observed that the extracellular dehydrogenase played a dominant role in the reaction process when the magnetic field intensity is 25 m T.