Study On The Effect Of Multi-walled Carbon Nanotubes Loaded With Ofloxacin On The Toxicity Of Aerobic Activated Sludge

Nanomaterials(NMs)and antibiotics,which have been put into large-scale commercial use,can be entered into the sewage in large quantities during its produced,used and disposed.The enriched NMs and antibiotics in the sewage would severely affect the choice of treatment process for sewage plant and even impacts on the ecological environment.In this paper,making the MultiWalled carbon nanotubes(MWCNTs)and Ofloxacin(OFL)as the target pollutants.the toxic effect and mechanism of target exogenous on the aerobic activated sludge system were investigated.In which,the aerobic activated sludge system is by exposured to target exogenous(MWCNTs,MWCNTs-OFL composite nanomaterials and OFL).The main research content and obtained results are as follows.(1)MWCNTs have a strong adsorption effect on OFL.The adsorption process can be welldescribed by the quasi-second-order kinetic model and the Langmuir isothermal adsorption model.The entire adsorption process is mainly surface adsorption.The adsorbed MWCNTs-OFL composite nanomaterials and MWCNTs have no difference in appearance and morphology.Because of OFL is loaded on the surface,however,the surface functional groups of these two NMs are different.(2)Added MWCNTs,MWCNTs-OFL composites and OFL,respectively,the biological removal of COD,ammonia nitrogen,and soluble orthophosphate in sewage has no obvious effect on MWCNTs after 24 hours of short-term action,but MWCNTs-OFL composite material and OFL have obvious inhibition.The suppression of OFL injection is stronger than that of MWCNTs-OFL composite.The effects of the three substances on nitrogen and phosphorus removal are related to the inhibition of the activities of AMO,NOR,NAR,NIR,PPX and PPK enzymes in the cells of microorganisms.(3)The addition of MWCNTs had no significant effect on the surface and respiration of aerobic activated sludge cells,nor on GR activity of microorganisms.There was no significant increase of dead bacteria in the activated sludge system.However,after adding MWCNTs-OFL composite material and OFL,the microbial cells were severely deformed and wrinkled,respiration and GR activity were inhibited,dead bacteria in the activated sludge system increased significantly,showing obvious toxic effects,and the toxicity was produced by OFL.(4)The addition of MWCNTs has little effect on the microbial cell LB-EPS,but after the addition of MWCNTs-OFL composite material and OFL,the tryptophan-like substances in the microbial cell LB-EPS are reduced,which stimulates the cells to secrete a large amount of like humic acid and fulvic acid reduce the toxicity of OFL to cells.Compared with OFL directly,MWCNTs-OFL composites stimulated cells to produce more humic and fulvic acid-like substances,which better reduced the toxicity of OFL.(5)The addition of MWCNTs had no effect on the replication and synthesis of microbial DNA,but the addition of OFL had an effect on the replication and synthesis of microbial DNA in aerobic activated sludge,showing a concentration-dose relationship.MWCNTs failed to exert the role of nano-injectors,failed to promote OFL transport into cells,and enhanced DNA toxicity.Of the three exogenous substances,the addition of OFL can significantly reduce the microbial community abundance and affect its structure.In general,the short-term effect of adding MWCNTs for 24 h is not obvious for aerobic activated sludge.Under the same short-term effect,the MWCNTs-OFL composite material formed by adsorption in water has less toxicity to aerobic activated sludge than OFL dissolved in water,and the toxicity is mainly caused by OFL.