Dissolved Organic Matter Modified Magnetic Carbon Nanotubes Composite Enhance The Bioremediation Of Cr(Ⅵ) And Azo Dyes

The rapid development of the printing and dyeing textile industry makes dye wastewater become an important source of industrial wastewater pollution.Heavy metals are always used as mordants to enhance the fixation dye effect.Hence,a large amount of heavy metal-containing dye wastewater is generated.Due to complex composition,high toxicity（teratogenic,carcinogenic,and mutagenic）and stubbornness,heavy metal and dye pose great threats to human health and environmental ecosystems.Therefore,it is of great significance to explore green and efficient treatment methods for the treatment of heavy metal and dye wastewater.In this study,carbon nanotubes（CNTs）are used as carriers which possess the characteristics of high specific surface area,good electrical conductivity,ductility and dispersibility.Magnetic carbon nanotube composites modified by sodium anthraquinone-2-sulfonate（AQS）and humic acid（HA）were synthesized by chemical and calcination methods,they are marked as AQS/Fe₃O₄/CNTs and HA/Fe₃O₄/CNTs.The composites are used to the bioremediation of Cr（VI）and methyl orange.The surface morphology,particle size,crystal structure,functional group composition,specific surface area,magnetic saturation and electron transfer capabilities of composites are characterized by means of a series of characterization methods.The results demonstrate that the specific surface area of AQS/Fe₃O₄/CNTs is 14.91 m² g^-1,which is larger than that of HA/Fe₃O₄/CNTs(5.88 m² g^-1).Therefore,AQS/Fe₃O₄/CNTs provides more reaction sites,the higher specific surface area of AQS/Fe₃O₄/CNTs may contribute to its higher efficiency in the bioreduction of Cr（VI）and methyl orange.In addition,both the two composites exhibit great superparamagnetism,which make solid-liquid separation achieve quickly under the action of an external magnetic field,thus,it conduces to the recycle of materials.The results of bioremediation experiments show that DOM/Fe₃O₄/CNTs composites can mediate the reduction of Cr（VI）and methyl orange by microorganisms efficiently.However,low concentration of DOM cannot provide enough electrons for the removal of Cr（VI）and methyl orange,and high concentration of DOM can also inhibit the bioreduction due to its biotoxicity.Alkaline conditions（p H=8.0）are more favorable for the bioremediation of Cr（VI）and methyl orange.At the same time,DOM/Fe₃O₄/CNTs composites exhibit great mediation effects in single system（with Cr（VI）or methyl orange alone）and binary systems（with Cr（VI）or methyl orange in combination）,and the biotoxicity of treated wastewater is significantly reduced.After3 cycles experiments,both the reduction rates of Cr（VI）and methyl orange decrease by less than 10%.16S r DNA high-throughput sequencing shows that Enterococcus and Klebsiella have significant ability to remove Cr（VI）and methyl orange under anaerobic environment.The reduction of Cr（VI）and methyl orange is mainly ascribed to the synergistic effect of Fe（II）/Fe（III）and DOMre/DOMox.In summary,this study provided an innovative method for simultaneous bioremediation of organic pollutants and heavy metals.