| Due to the increasing emissions of bilge oily sewage, and the stricter emissions standards setted by International Maritime Organization (IMO), the traditional physical separation method has been unable to meet the requirements of oil sewage emissions. The construction of the advantage bacterium group in the MBR, and combination with magnetic strengthening technology for bilge oily wastewater treatment were studied in this paper. It takes two step screened mixed bacteria with high efficient oil degradation ability as the target,and mainly study the oil removal efficiency enhanced by magnetic fields and its mechanism to improve the biodegradable efficiency of oil.Giving priority to the oil removal rate and considering microbial growth capacity, A3, A7,B5, B11 were selected as advantage strains due to the fact that the oil removal rate of the four strains were over 50%. Through building the mixed bacteria in the form of random combination, the mixed bacteria composed by A3, A7, B11 had the highest degradation rate,reached 60.8%, which was about 10% higher than single strains. And the initial oil concentration of 500-1000mg/L, temperature of 30 ℃, initial pH of 6-8, table speed of 100 r/min were declared as the best cultural conditions. By studying the morphology characteristics, physiological and biochemical properties and 16S rDNA, A3, A7, B11 were identified as Gordonia, Rhodococcus, Acinetobacter respectively.The growth and the oil removal efficiency of the mixed bacteria composed by A3, A7,B11 were investigated under different magnetic field intensity and magnetic stimulative time.The results showed that the intensity of magnetic field had an critical effect on single strains and mixed bacteria. The highest oil removal rate of the mixed bacteria reached 70.7% and the characterization of biomass OD600 reached 0.869, which were 10.1% and 13.5% respectively higher than without magnetic field when the magnetic field intensity was 25mT. Magnetic field had no effect on the growth of the mixed bacteria in adaptive period, but promoted the growth in the logarithmic period and stable period. OD600 of the mixed bacteria reached 1.052 in the fourth days, which was 15.1% higher than no magnetic field. The result of response surface analysis showed that the magnetic field intensity and magnetic stimulative time had a synergistic effect on the oil removal,and magnetic field intensity played a leading role in the process of strengthening oil removal.Through the measurement of oil components, oil metabolic pathway and microbial enzyme activity,the oil removal mechanism of the mixed bacteria simulated by magnetic field was analyzed. The synergy played between strains in the process of oil degradation. And magnetic stimulation could obviously promote the mixed bacteria to degradate saturated chain hydrocarbon (especially short chain alkanes and odd number carbon saturated hydrocarbon).In the process of oil degradation of the mixed bacteria, the oil removal rate could be increased obviously on the surface adsorption, transmembrane intaking, biodegradation of secretive enzyme in different parts by adding magnetic field. The intensity of magnetic field had an critical effect on dehydrogenase activity of the mixed bacteria. The highest intracellular dehydrogenase activity and extracellular dehydrogenase activity reached 19.1 TFμg/L-h-1 and 41.6 TFμg/L·h-1 respectively, which were 27.3% and 32.5% higher than no magnetic stimulation when the magnetic field intensity was 25mT. In addition, extracellular dehydroge-nase was dominant in the process of the dehydrogenation and more significant influence than intracellular dehydrogenase affected by magnetic field. |
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