Study On The Effects Of Biochars And Multi-walled Carbon Nanotubes On Atrazine Biodegradation By DNS32

Biochars?BCs? and carbon nanotubes?CNTs?are the most important bio-carbon materials and graphitized carbon materials.They have been developed as environmental functional materials due to their special structural characteristics and excellent adsorption properties,and show significant value in soil improvement and environmental pollution remediation.However,with the large number of BCs and CNTs applications,the potential environmental risks are also of concern.At present,there are some reports on the biological toxicity of CNTs,but it is controversy.The impact of BCs on bacterial activity is rarely reported,and there is little report on whether BCs and CNTs will further affect microbial degradation by affecting microbial activity.Based on a large number of relevant literatures,the effects of BCs and CNTs on atrazine biodegradation and the biological effect of the degrading bacteria,Acinetobacter lwoffii DNS32.Biochars resulted from corn straws?C-BCs?and banana peel?B-BCs?and Multiwalled carbon nanotubes?MWNTs?are chosen as the examples.The main conclusions are as follows:?1?Using scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and Raman spectrometer,structure of biochar or MWNTs was epitomized.SEM images showed that BCs well retained the naturally formed microstructure,in which C-BCs consisted of pores of several microns in diameter,and the surface of B-BCs were rough and had a distinct porous structure.The images of TEM and Raman spectra showed MWNTs have a diameter of 10-100 nm and a length of several hundred micrometers.The MWNTs of different diameters have different degree of graphitization.The local zeta potential is low,where may be a large amount of the oxygen-containing functional groups.?2?The effects of C-BCs,B-BCs and MWNTs on atrazine bio-degradation by DNS32 were studied.The results showed that the degradation efficiency of atrazine was higher when C-BCs,B-BCs and MWNTs increased from 10 to 100 mg/L,decreased by 12.7%,60.0% and 63.7% respectively.The results of fluorescence quantitative PCR showed that the degradation genes of atrazine were down-regulated by high concentration of three materials,but the reduction of C-BCs was very small.Therefore,C-BCs have the least effect on the biodegradation of atrazine by DNS32 in the three materials.?3?The effects of C-BCs,B-BCs and MWNTs on the activity of DNS32 were investigated.The results showed that C-BCs,B-BCs and MWNTs at the concentration of 10 mg/L promoted the bacterial activity by 14.5%,6.6% and 12.3%,respectively,while at the concentration of 100mg/L,the three kinds of materials,respectively,inhibited the activity by 5.7%,23.4% and 30.2%.Moreover,transmission electron microscopy showed the cellular membrane of DNS32 were destroyed by B-BCs and MWNTs,but C-BCs had little effect on the morphological structure of cellular membrane.This means that B-BCs and MWNTs are biotoxic,both of which interact with the cellular membrane,causing physical damage,thereby inhibiting cell activity.Whereas C-BCs have higher environmental safety because they do not exhibit biotoxicity even at higher concentrations.?4?It is assumed that the cytotoxicity of B-BCs is due to the introduction of toxic substances such as Zn²⁺ in the process of its modification,and the cytotoxicity of MWNTs is due to its nano-size and further studies on the bio-toxicity mechanism of B-BCs and MWNTs were exploreed.The results showed that the content of Zn²⁺ had little contribution to B-BCs' biotoxicity.E.coli and B.subtilis were used as control microorganisms to explore the biotoxicity mechanism of MWNTs.The results showed MWNTs could change the bacterial cellular membrane permeability and the fatty acid composition of the bacterial cellular membrane,and the smaller the diameter of MWNTs,the larger the change range,indicating that the smaller the MWNTs nanometer size are,the greater the cytotoxicity is.?5?The immobilized DNS32 were prepared using the C-BCs as the carriers.The degradation rate of immobilized DNS32 can reach 94% in 40 h.And compared with the free bacteria,the immobilized DNS32 show better adaptability to p H and better cold tolerance.In the simulation experiments treating atrazine pollution water,the immobilized DNS32 were still active after 30 d.