Study On Decolorization Process And Mechanism Of Alcaligenes Faecalis LJ-3 On Azo Dye

With the rapid development of dye production and textile printing and dyeing industry,the wastewater containing dyes has become one of the main pollution sources of water in China.M ost dyes and their degradation products have biological toxicity,which seriously threatens humanhealth and the ecological environment in which they live,therefore,harmless treatment of dye wastewater is particularly important.Microbial treatment of dye wastewater is low cost,high effi ciency and environmental friendliness,and has wide application prospects.It can build a foundati on for the biological treatment of dye wastewater by screening of highly efficient decolorization strain,optimization of decolorization process and studying the decolorization mechanism.In this paper,a highly efficient azo dye-degrading strain LJ-3 was isolated from the sludge and soil that was sampled from the wastewater treatment pools of Lucheng dyeing and printing plant in Wenzhou and the surrounding long-term dye-contaminated soil by enrichment culture.Th e strain was determined as Alcaligenes faecalis through morphological observation,physiologicaland biochemical experiments,PCR amplification and 16S rDNA identification.The degradation characteristics of LJ-3 on acid scarlet 3R under different conditions(such as dissolved oxygen,medium composition,initial pH,temperature,NaCl concentration and dye con centration)were analyzed,and the decolorization conditions were optimized by statistical methods.It was found that the degradation efficiency of the strain on acid scarlet 3R increased with the increase of cell concentration(represented by OD600),and the degradation efficiency was higher in standing condition than that in 160 r/min shaking culture.From the analysis of the degradati on characteristics,it was found that the strain could degrade acid scarlet 3R at 15?45 ?,pH 5.0?11.0 and NaCl concentration of 0.05%?3%,and the decolorization rate was above 95%in 48 h.Mg2+ and Ca2+ can improve the decolorization rate.When the concentration of acidscarlet 3R was in 100 mg/L-1000 mg/L,the degradation rate of the strain could keep above 95%.The main effect factors were selected by PB design,and then optimized by response surfac e design.Optimum operating conditions for decolorization were as follows:yeast extract 2.9 g/L,Na2HPO4 3.5g/L,temperature 39.5? and the dye concentration 40 mg/L.The best predictivedegradation rate was 94.5%.The test experiments showed that the decolorization rate of 40mg/L acid scarlet 3R was 94.0%within 2.5h,and the experimental results were verified in the confid ence interval of the experimental model.In addition,under the optimal conditions,the decoloriza tion kinetics of the strain on acid scarlet 3R was accorded with logarithmic kinetic model(R2 =0.8522).At the same time,the degradation of the strain LJ-3 on other dyes was tested.The results showed that the strain cultured in 100 mg/L methyl orange,brilliant scarlet GR,acid red 88,reactive brilliant red X-3B,amaranth,amino black 10B,acid black 210,Sirius red and orange G.The degradation rates were respectively 95.51%,96.7%,94.65%,93.89%,98.70%,92.62%,85.3%,93.39%and 84.84%.indicating that the strain can effectively degrade azo dyes,and be of a potential practical application.Finally,the decolorization mechanism of the strain on the acid Red 3R was analyzed,and the UV-vis spectra showed that the maximal absorption peak of acid Red 3R at 508 nm disappeared after the decolorization treatment by strain LJ-3(2.5 h),and a lot of absorption peaks in the range of 200?400 nm appared.It can infer that the macromolecular substance is transformed into small molecule comopounds by the LJ-3 strain.Enzyme activity analysis showed that significant laccase,NADH-DCIP reductase and azo reductase activity were determined in experimental group(2.5 h)when compared with that in control group,demonstrating that the decolorization of acid red 3R by strain LJ-3 was conducted by the co-action of these enzymes.In summary,the strain A.faecalis LJ-3 is a potential dominant bacterium for treatment of azo dye wastewater.