| Dyes are widely used in various industrial fields such as textiles,printing,dyeing and papermaking.The annual discharge of dye-containing colored wastewater was nearly 7×10~8tons in our country.The wastewater even that discharged from a single plant inevitably contains complex pigments because different types of pigment are employed based on dyeing colors and textile properties.Most of these dye components have exhibited carcinogenicity,teratogenicity and mutagenesis for humans and other organisms,meanwhile,they are intentionally designed to be resistant to light,water and oxidizing agents,making them difficult to remove once they are released into the environment.Microbial decolorization technology is an effective method for treating industrial colored wastewater.However,there are some restrictions and limitations for treatment actual wastewater with the conventional decolorizing microorganisms,such as single decolorizing substrate and poor adaptability to environmental conditions,which are difficult to meet the actual process requirements.Therefore,developing new decolorizing microorganisms with Broad spectrum and adaptability,and exploring the decolorization mechanism which can lay the foundation for the biological treatment of dye wastewater.Here,we report a strain of Aspergillus flavus named A5p1(CGMCC.4299),which is used as biological material to study the decolorization characteristics of azo dye Direct Blue 71(DB71),phthalocyanine dye Direct Blue 86(DB86)and anthraquinone dye Reactive Blue 19(RB19).At the same time,the practical application potential of the strain is discussed by constructing a bioreactor,and modern analysis methods are used to conduct in-depth research on the decolorization mechanism of the dye.The main research contents of this paper are as follows:(1)Characteristics of dye decolorizaing strain Aspergillus flavus A5p1.Fifteen dyes representing the above four types were chosen to test the decolorization ability of A5p1.The results showed that the decolorization of A5p1 to the dyes was 61.7%-100.0%,indicating that the A5p1 has a certain broad spectrum of decolorization.Three dyes,including Direct Blue 71(DB71),Direct Blue 86(DB86)and Reactive Blue 19(RB19),were selected for comparing decolorization mechanisms.The results showed that the decolorization mechanism of A5p1 for azo dyes and phthalocyanine dyes were mainly biosorption,and for anthraquinone dyes was biodegradation;Under acidic conditions,the biosorption was dominant in dyes removal process,under alkaline conditions,biodegradation was the main decolorization mechanism;when the dye concentration was higher than 500 mg/L,the decolorization of azo dyes and phthalocyanine dyes were dominated by biodegradation,and the dye concentration was lower than 500 mg/L,biosorption played an important role in dye decolorization.The broad spectrum and the flexibility of A5p1 for decolorizing dyes reflected that the strain can adapt to the actual wastewater treatment requirements with variable conditions and have good application potential.(2)Degradation mechanism of various types of dyes by Aspergillus flavus A5p1.A5p1 showed the high decolorization rate(100%-75.8%)to high concentration Direct Blue 71(DB71)(100-1000 mg/L),the optimal degradation conditions were p H7.0,30-40℃.The degradation products of azo dye DB71obtained by(GC-MS)and(LC-MS)analysis were mainly naphthylamine,naphthalene diazonium,2-hydroxy-6-oxalyl-benzoic acid and 1-naphthol.Enzyme analysis experiments showed that manganese peroxidase(Mn P),laccase(Lac)and glucose oxidase(GOD)were related to the degradation of azo dyes by this strain.For the high concentration(100-2000 mg/L)of Direct Blue86(DB86)and Reactive Blue 19(RB19),the decolorization rate was 100%-80%and 100%-50.8%,respectively,and the optimal degradation were p H 7.0 and temperature 30-40℃.The degradation product of phthalocyanine dye DB86 was phthalimide,and the degradation product of anthraquinone dye RB19 was mainly phthalic acid and 2-amino-1-phenol-4-sulfonic acid.Enzyme analysis experiments showed that the activities of manganese Mn P,Lac and GOD were detected during the decolorization of dye DB86,and the activities of manganese Mn P and GOD were detected during the decolorization of dye RB19.(3)Research on the dye removal by Aspergillus flavus A5p1 in bioreactors.A packed bed bioreactor with a working volume of 250 m L was designed and operated for the simulated dye wastewater.The bioreactor treats single-component dye wastewater.The system runs for 20 days,and the effluent decolorization rate remained above 90%.The mixed dye wastewater treatment system runs for 30 days,and the effluent decolorization rate remained at 80%.When the inlet dye concentration was greater than 500 mg/L and p H was gradually increased from 5.0 to 9.0,the bioreator steadily run for 50 days with the effluent decolorization of 70%and still maintained degradation activity,indicating a good operating stability of the system and the practical application potential of the strain.(4)The adsorption mechanism of Aspergillus flavus biosorbent.The adsorption characteristics of the Aspergillus flavus biosorbent were investigated.The results showed that the straiin not only has a significant adsorption capacity for dyes,but also can withstand higher ambient temperatures(40°C).The maximum adsorption capacities of the three dyes were 134.1 mg/g(DB71),139.8 mg/g(DB86)and 43.9 mg/g(RB19),respectively.The potentiometric titration and FTIR were used to analysis the functional groups on A5p1,the amino groups on the surface of the biosorbent were the responsible mechanism of binding of A5p1 and dyse.The results of kinetic and thermodynamic showed that the adsorption process of A5p1 biosorbent on DB86 was physical adsorption,RB19 was chemical adsorption,and DB71 was a combination of the two,indicating A5p1 biosorbent has different adsorption behaviors for three dyes.Confocal laser microscopy(CLMS),atomic force microscopy(AFM)and transmission electron microscopy(TEM)analysis confirmed that the dye DB86was mainly adsorbed on the cell surface,DB71 and RB19 can adsorb inside the cell.This result showed that the DB71 and RB19 could also obtain more adsorption sites inside the cell to continued the adsorption reaction after the rapid physical adsorprion was compeleted on the surface of A5p1,the adsorption process presented diversity and complexity.For the DB86,due to the limitation of adsorption sites on the surface of A5p1,the dyes could only perform a simple adsorption process mainly on the cell surface with physical adsorption.Therefore,different dyes were adsorbed at different positions on the adsorbent,which may be the reason for the A5p1 has different adsorption behaviors for different dyes. |
