Study Of High-salt Azo Dye Wastewater Treatment By Exiguobacterium Sp.TL And Its Performance

The purpose of this dissertation is to establish a high-salt azo dye treatment method which not only can effectively and stably decolorize but also mineralize dyes. The study was started from the investigation of efficient salt-tolerant and azo dye-reducing microbial community, mainly including the impact of initial dye concentration, salinity and metal ions from. An efficient salt-tolerant azo dye decolorizing bacterial strain was isolated, identified and its characteristics were investigated. Then the co-augmentation effect of the strain and anthraquinone on azo dye biodecolorization by activity sludge system for further improvement was studied. Finally, the synergism of a Penicillium and bacterial strain was used to promote the mineralization of azo dyes by only microbial treatment method. The contents of this dissertation were as follows:The influences of initial dye concentration, salinity and metal ions on azo dye decolorization by a wild soil microbial consortium were investigated. The results showed that when the initial concentration or salinity increased, the impact to the decolorization of simpler-structure dyes was less. Some metal ions would inhibit the activity of microbial community and the order of inhibition was as follows:Cu2+> Al3+ and Zn2+> Mg2+, Ca2+and Pb2+. Besides, as the concentration of metal ions increased, the inhibition effects of Al3+and Zn2+ increased, but there was little change for Mg2+ and Ca2+. DGGE fingerprint showed the dynamic shifts of microbial community structures and the dominant species were mainly belonging to Bacillus, Pseudomonas, Sedimentibacter, Clostridiales, and Streptomyces.A salt-tolerant bacterial strain which could decolorize azo dyes was isolated and was named as TL. It was identified as genus Exiguobacterium by morphology, physiology and biochemistry and 16S rDNA sequence analysis. The 16S rDNA sequence of strain TL had been deposited in the GenBank database under accession number EU159578. It was identified as a novel azo dye-reducing and salt-tolerant bacterium according to the previous reports.The characteristics of strain TL were investigated and the optimal conditions for growth and decolorization were:inoculum amount 6% (v/v), pH value 5.4-7.0, temperature 30-40℃, salinity (NaCl)≤15%(w/v). Mg2+ and Ca2+ promoted decolorization, however, Al3+, Zn2+, Fe3+ and Cu2+ could inhibite the process in different extent. Strain TL could not decolorize azo dyes efficiently when using glucose, sucrose and lactose as carbon source. Whereas, it could grow and decolorize azo dyes depending on several inorganic nitrogen source. Decolorization of active brilliant red X-3B in the medium containing peptone as carbon source followed the first-order reaction kinetics. The kinetics constants were about 0.22-0.26 mg/(L-h) when the initial dye concentrations were not more than 700 mg/L, and it decreased to nearly a half when the initial dye concentrations were higher than 700 mg/L. Decolorization of azo dye by strain TL was identified as typical azo reduction pathway by UV-Vis and LC-MS.The redox mediator anthraquinone could catalyze the reduction of azo dyes by the whole cells of strain TL and the optimal conditions were:initial dye concentration less than 75 mg/L, anthraquinone concentration 0.6 g/L, inoculum amount 6 g/L (wet weight), temperature 30-40℃(optimum of 30℃), pH value 3.0-4.0 (mainly bio-adsorption) and 7.0-9.0 (mainly bio-reduction). Compared with Na+, Mg2+ and Ca2+ could promote the decolorization; Zn2+, Al3+, Fe3+and Cu2+ inhibited it. The activated sludge system which was started-up by bioaugmentation with strain TL firstly and then enhanced by anthraquinone was determined as the most efficient mode of co-augmented system. This process realized both of fast-start-up and efficient & stable operation. Compared with non-augmented system, the start-up time was 2.5 d shorter and the color removal loadings were about 1000 mg/(g-d) (initial dye concentration was about 700 mg/L),500 mg/(g-d) (initial dye concentration was about 1000 mg/L), respectively. The results of PCR-DGGE showed that the the consortium was stable and strain TL could co-exist with the aboriginal microorganisms in the activated sludge.Penicillium sp. strain QQ was introduced to the azo dye wastewater treatment system in order to improve the biodegradability of the effluence of anaerobic unit. The optimal decolorization conditions by the synergism of strains TL and QQ was optimized and simulated by response surface methodology (RSM), and the results were:inoculum of strains TL and QQ were 1.09 g/L and 132.67 g/L (wet weight), concentrations of glucose and yeast extract were 2.25 g/L and 2.10 g/L, temperature 33.0℃, pH value 6.50, initial concentration of active brilliant red X-3B 235.14 mg/L, respectively. The inoculum of strain QQ and yeast extract concentration showed synergistic effect on decolorization. ANOVA results demonstrated that the model and tested factors were significant to decolorization by the synergism system. HPLC results showed that some compounds of low molecular and high polarity might be produced in the synergism system. Whereas, the major decolorization products in the system only contained bacterial strain TL might be high molecular compounds, which was inferred as corresponding aromatic amines and their auto-oxidation and auto-polymerization products. The anaerobic unit inoculated with strains QQ and TL followed by the aerobic unit inoculated with activated sludge were chosen as the optimal combined biological process. The dye could be mineralized with this combined process.