Study On Decolorization And Degradation Of Reactive Black5by The Flora FF

Recently, with the rapid development of dye production and textile printing industry, the wastewater it produced has become one of most difficult wastewater to deal with. At the same time azo dyes were important pollutants in wastewater. Bacterial consortium, which has many advantages such as stable effect and degradation of dyes thoroughly, has become a focus research point in dye wastewater treatment technology. Screening and studying mixed flora which have excellent decolorization performance will provide a theoretical basis for the large-scale biological treatment of dye wastewater. In this study, a bacterial flora capable of decoloring Reactive Black5effectively has been screened from a well-running textile printing wastewater biological treatment system (A+OSA activated sludge of excess sludge reduction system) on the2nd anaerobic reactor, through the method of domestication with gradient concentrations. We conducted a series of studies for its decolorization performance, decolorization mechanism and composition of microbial communities.We studied the decolorization performance and dynamics of the dye Reactive Black5by the flora FF. Results of the dye decolorization experiments suggested that the flora FF could give an average decolorization rate of84.6%for Reactive Black5of200mg/L under the optimal culture conditions:temperature of35℃, pH of8.0and static culture with12h. After24h, the highest decolorization rate reached94.8%. When it was continually cultured for150generations, it still had stable decolorization effect. At the same time, the flora FF had a good decolorization performance for Reactive Blue19. Reactive Orange1and Reactive Red3BFN, all of which were small molecular reactive dyes. When static cultured for24h, the decolorization rate reached more than90%; The salt tolerance results showed that FF had maximum tolerated NaCl concentration is4%, and after24h the decolorization rate remained at91.0%. The flora FF has a strong ability of lasting decolorization. it may continuous decolorize six batches and the decolorization rate still keeped at57.3%. The flora FF’s decolorization dynamics was studied, when the concentration of Reactive Black5less than1500mg/L, FF’s biological decolorization reaction in accordance with (Monod) equation is apparent zero-order kinetics reaction, in the first12h.The impact of different carbon, nitrogen sources in medium and different exogenous material on the growth and decolorization of the flora FF were also studied. In the carbon source experiment. FF’s decolorizing results was best of82.1%when the carbon source was sucrose. In the nitrogen source experiment. FF’s gowth and decolorization overall effect was best, and the decolorization rate of73.1%when the nitrogen source was peptone. Variety C, N sources experiment showed that FF’s growth and decolorization effect were not good in mineral medium conditions with different carbon and nitrogen sources as in beef extract peptone medium, this may be related to the fact that the flora FF were domesticated and screened in beef extract peptone medium at the start. The influence of different metal ions were also studied, Zn2-, Sn2-, Co2+were seriously inhibit the growth of bacteria, in the initial time (before8h), Mn2+. K+. Mg2+, Ca2+have active effect on decolorization, while Sn2+, Co2+have inhibitory action, when the concentration of metal ions were1mmol/L in the reaction system, But in the subsequent decolorizing time, none of the various ions cause a great impact on decolorization, After24h, the decolorization rate was basically the same as91.0%. The influence of electron acceptors was studied, it was showed that iron citrate, sodium nitrate can slightly promote bacterial growth, and iron oxide with no significant effect, but sodium nitrite, sodium thiosulfate may be slightly inhibit the growth of FF. In the first12h, citric acid iron, sodium nitrate, ferric oxide, sodium nitrite and sodium thiosulfate these electron acceptors all can obviously reduce decolorizing efficiency of the flora FF to Reactive Black5. The impact of different electron donor(mainly coenzyme NADH and NADPH) on the flora FF’s growth and decolorization was examined. The results showed that in the NADH and NADPH’s concentration of0.5mmol/L, the whole process of FF’s growth substantially the same as with no coenzyme, but the decoloration rate declined, after48h, the decolorization rate of FF with no coenzyme was95.4%, while the decolorization rate of FF plused NADPH and NADH reduced to90.7%and85.1%. It showed that the process that FF decolorized and degraded Reactive Black5with no need of NADH and NADPH under static culture conditions. These results can provide data basis for the selection of activator in the flora application process.In addition, the LC-MS was used in conjunction with the determination of Reactive Black5decolorization and degradation products, the analysis of the degradation mechanism have already inferred. The degradation mechanism can interpret for two kind possibilities, the first was:firstly. Reactive Black5shedd auxochrome groups-OH,-NH3,-SO3-and Na+, with the role of hydrolysis, then-N=N-double bond reductive cleavage into aromatic amines in the catalytic role, two-N=N- were cleavaged one by one. finally, a portion of the aromatic amine mineralized into small molecule metabolites under aerobic conditions. The second was:Reactive Black5is reductive cleavage the-N=N-double bond to generate aromatic amines under anaerobic conditions. There is a difference between degradation mechanisms of Reactive Black5effected by flora FF and reported single bacteria strain. Meanwhile, to different stages of the decoloration and degradation solution, through the E. coli toxicity experiment, we learned that the flora FF could reduce the toxicity of the dye in the process of decolorization and degradation of Reactive Black5.Finally, through denaturing gradient gel electrophoresis (DGGE), restriction fragment length polymorphism (RFLP), pure culture of the16S rDNA identification etc technologies to analysis the composition of microbial communities of the flora FF. DGGE and RFLP results showed that the dominant groups in the flora FF were Gamma-proteobacteria Proteus bacteria and Clostridia Clostridium bacteria. At the same time21strains, which had different decolorization rate, were selected randomly by pure culture technology. After16S rDNA identification,21strains were Gamma-proteobacteria bacteria (Klebsiella71.4%and Proteus28.6%). Among21strains, there were two strains had the best decolorization rate, which were Klebsiella sp. and Proteus sp. These results suggested there were culturable functional advantages bacteria in the flora FF such as Klebsiella and Proteus bacteria, as well as growth advantage species, such as Clostridium, which difficult to be cultured. While Proteus bacteria in the flora FF was both the growth dominant and functional advantages genus, which was also easy to be isolated and cultured, beneficial to application.