Mechanism Of The Strengthening Effect Of Nano Bamboo Charcoal On The Biodegradation Of PAHs

With the rapid development of nanotechnology,nano bamboo charcoal is widely used in textiles,plastics,coatings,etc.Nano bamboo charcoal(NBC)is inevitably released into the environment during its production,transportation,usage and disposal processes.Although bamboo charcoal in nontoxic,it may pose a potential risk on the environment when its particle size decreases to nanoscale.Therefore,it is necessary to investigate the interaction and operation mechanism between NBC and microorganisms,expecting to provide scientific evidence for the application of nano bamboo charcoal in bioremediation of polycyclic aromatic hydrocarbons(PAHs)polluted water.The PAHs-degrading strain Sphingomonas sp.GY2 B,which was screened by our lab in the earlier stage,was chosen for studies on the biodegradation of PAHs under the effects of NBC.Then a series of experiments including characterization of NBC,the effects of NBC on PAHs and on the strain were carried on to discuss the mechanism of the strengthening effect of NBC on the microbial degradation of PAHs.Results showed that the removal efficiencies of phenanthrene increased with the increasing NBC dose.At 24 h,the removal efficiencies of phenanthrene in the biodegrading system with 20,50,200 mg·L-1 NBC were 84.7%,92.2% and 93.0% respectively,which increased by 10.3%-18.6% compared to the control(74.4%).And the removal efficiencies were higher than 95% at 48 h.With regard to the more chemically complex and more difficultly removed crude oil,NBC could also promote its removal efficiencies.Elemental analysis result showed that NBC contained more than 60% of carbon and had a low H/C ratio(0.210).The lower H/C ratio indicated that NBC has a higher aromaticity,good biological stability,good chemical inertness and the ability of resistance to the microbial decomposition.And a large BET surface area(709.5 m2·g-1)and developed microporous structure were found in this study,which indicated that NBC have a strong adsorption capacity.In addition,NBC makes a negligible contribution to the solubilization of phenanthrene in water.And most of the phenanthrene adsorbed on NBC could be extracted by different organic solvents into the MSM,which made the residual rate of phenanthrene higher than that of the actual situation.It suggested that the strengthening effect of NBC on the biodegradation of PAHs may be attributed to the synergistic effect between adsorption and biodegradation.The growth curve of GY2 B showed that NBC posed a slight inhibition on the early growth period of the strain.After incubating for a longer period,systems added with NBC displayed a better growth momentum in general than that of the control.Images of the scanning electron microscope(SEM)indicated that slight deformation and more secretion of extracellular substances happened to cells under the impact of NBC.Some of the extracellular substances connected the cells with NBC,which might accelerate the utilization of phenanthrene adsorbed on NBC by the strain.What's more,some relatively small NBC particles were observed adhered to the outer membrane of bacteria,providing a possibility for cellular uptake of NBC.Transmission electron microscope(TEM)result showed that NBC could adsorb on the outer membrane,embed in the cells and also enter into the cells.Then cell sap was extracted by cells wall breaking and result showed that phenanthrene adsorbed on NBC could be desorbed in the cell sap.In other words,once NBC internalized in the cells,phenanthrene sorbed on them may be desorbed in the cell sap and degraded by ribosome or some internal emzyme.It could also improve the removal efficiency of phenanthrene.