Study On The Mechanism Of The Decolorization Of Biological Degradation Azo Dyes

Azo dyes are widely used in textile printing,food,paper and printing industries,accounting for about 70%of the total textile dyes used,and are the most widely used class of synthetic dyes in various industries.Azo dye wastewater has high chroma,chemical stability and poor biodegradability.The Bulk and degradation products of aniline intermediates are toxic,teratogenic,mutagenic and carcinogenic,etc.One of the difficult to treat wastewaters recognized at home and abroad.These toxic substances cause great harm to the health of humans,animals and plants in the water environment for a long time.Therefore,the treatment of printing and dyeing wastewater containing azo dyes has become one of the research hotspots at home and abroad.Azo dye hair color key is azo bond(-N=N-)and azo bond has a strong electron affinity in the process of biological treatment.Azo dyes decolorizing need by azo bond rupture.Anaerobic microbes can degradate azo dyes under using four electrons and protons.However,the anaerobic microorganism decolorization rate is slow,and decolorization requires longer hydraulic retention time.So it requires a large reaction volume to ensure that the organism has enough time to degrade azo dyes.In order to overcome the limitation of biological decolorization rate and reaction cycle,this paper explores the best condition of the biological decoloring azo dyes and the method of improving the ability of biological decoloring azo dyes were studied,the main research content is as follows:(1)Firstly,a bacterial strain which was isolated from the activated sludge,has remarkable ability to decolorize azo dye A07.This bacterial strain belongs to Aeromonas hydrophila according to 16S rRNA gene sequence analysis,and was identified as Aeromonas hydrophila strain JL-1.Secondly,the optimum decolorization condition was studied.The results showed that the strain JL-1 could effectively decolorize azo dye A07 under anoxia oscillation culture.The environmental conditions such as culture medium,initial dye concentration,inoculation amount,pH and NaCl concenrtration had obvious effect on the decolorization performance and growth of the strain JL-1.The optimum decoloring and growth condition for the strain JL-1 was the Luria-Bertani medium with pH 5.0,salinity 1%,temperature of 30 ℃,rotating speed at 150 rpm.Under this optimum condition,the decolorization efficiency of 100 mg L-1 azo dye A07 by the strain JL-1 is more than 95%.In addition,the strain was salt tolerant and can still be used for effective biological decolorization within 3%salinity.(2)Firstly,anaerobic sequencing batch reactor(ASBR)was used to treat high concentration azo dye wastewater.Secondly,the effect of yeast extract and ferric hydroxide on the decolorization performance of the system was studied.The results indicate that the decoloring azo dye rate of the 100～500 mg L-1 azo dye A07 is 99.51%in the condition of low organic matter concentration.It is almost entirely decoloring.However,when the azo dye concentration increases to 600 mg L-1,azo dye decolorization,COD removal.and activated sludge precipitation growth and performance has a great impact that the system decoloring rate fell to 86.32%and appears the phenomenon of sludge bulking.Don’t change water quality components just increasing the concentration of organic matter.That can promote the growth of activated sludge in the system,and improve the decoloring rate.But it does not improve the impact that the high concentration of azo dye will inhibit the system function.The decoloring rate and settling performance will decrease.And it does not relieve sludge swelling.Solid iron hydroxide powder and yeast extract are added in the system.It can offset the impact that the system of decolorization performance is inhibited by the high concentration of azo dye.Meanwhile,it can prevent the occurrence of sludge expansion system and maintain system better settling performance.It can also enhance the system of azo dye decolorization rate and improve the removal rate of COD.The decolorization of azo dyes in the system conforms to the first order reaction kinetics model,and the decolorization rate is decreasing by the increasing of azo dye concentration.