Research On The Mechanism Of Carbon Nanotubes To Accelerated Anaerobic Degradation Of Azo Dye

Azo dye wastewater was one of the difficultly treated industrial wastewater because of its complex composition,high concentration of toxicity and large water quantity.In the water treatment process technology,the anaerobic-aerobic biological treatment process was the most effective and feasible way to be applied in the practice of azo dye wastewater treatment.However,There were also several disadvantages such as the low rate of reduction,the longer hydraulic retention time.In this paper,the performance of carbon nanotubes was evaluated as redox mediator to promote azo dye degradation in presence of anaerobic granular sludge.In this stuy,several technologys was adopted to characterize carbon nanotubes,showing that carbon nanotubes consist of agglomerates,the surface was grafted with various different oxygen-containing surface groups,carbon nanotubes possessing sp2 hybridizedcarbon configuration,the faulty long-range orderedcrystalline and the existence of disordered carbon structures.And the Langmuir isotherm equation and pseudo-first order adsorption kinetic provided the best correlation to describe the phenomenon that carbon nanotubes adsorbed azo dye.Carbon nanotubes accelerated the chemical reduction of azo dye by Na2S/PMS were aslo investigated.Results demonstrated that carbon nanotubes could significantly improve azo dye reduction.So it could be regarded as ideal redox mediator.Compered with activated carbon,the azo dye reduction rate was respectively 4.7 times during Na2 S syetem and 9.2 times during PMS systems in presence of carbon nanotubes.The intermediate products were analyzed with gas chromatography-mass spectrometry.The results showed that the reduction pathway was difference between Na2 S system and PMS system.The azo dye reduction mainly because electrons transfer from sodium sulfide to azo bond in order to achieve dye decolorization during Na2 S system.And degradation products were mainly aromatic amine.However,carbon nanotubes directed provided electrons to activate PMS to produce SO₄^-? for azo dye degradation during PMS system.And the removal of TOC achieved 43.1%,the degradation products were mainly aromatic oxygenated compounds.Two chemical experiments result could identify that carbon nanotubes possessed redox mediator features.It could also accelerate azo dye biodegradation when it was applies to anaerobic granular sludge process.The biodegradation rate increased 3.5 times?AO7?,5.0 times?OG?,2.5 times?CR?,3.4 times?DB71?,respectively when there were carbon nanotubes in anaerobic degradation system.Biodegradation process was according with the pseudo-first order and COD removal rate reached 40.5%.The experiments show that the type electron donor had obvious effects on azo dye biodegradation,with the mixing carbon source and sodium formate as the better electron donor.The biodegradation efficiency of azo dye increased with increasing sludge concentration,higher carbon nanotubes dosage or elevating carbon source amounts.Carbon nanotubes could also accelerate azo dye biodegradation in UASB reactor.The reactor in presence of carbon nanotubes compared to the reactor without more biodegradation of AO7 about 21.42 g.In conclusion,carbon nanotubes possessed redox mediator features.Carbon nanotubes could promote azo dye reduction and anaerobic biodegradation mainly had three mechanisms:?1?adsorption;?2?Carbon nanotubes played the part of electron acceptor to accelerate the electron transfer;?3?oxygen-containing surface groups and the ?-electron system of carbon nanotubes could direct provide electron to promote azo dye reduction.