Decolorization Of Dye Wastewater With High Salt Concentration By Halomonas Sp. GTW

Evaluation of the literature on anaerobic-aerobic treatment of azo dyes reveales possible bottlenecks: (i) high salinity of the dye wastewaters usually causes plasmolysis and/or loss of activity of cells, and some traditional aerobic- and anaerobic-biological treatments in low COD removal performance; and (ii) anaerobic azo dye reduction is a time-consuming process, reflected by the requirement of long reaction times. Hence, there is clearly a need for a salt-tolerant and efficient bio-treatment system for the removal of dye wastewaters with high salt concentration.The purpose of this dissertation is to investigate characteristics of a newly isolated halomonas sp. GTW with the ability to degrade dye wastewater at high salt concentration. The physiobiochemical and 16S rDNA molecular identification are carried out. The characteristics of strain GTW growth and azo dyes are also investigated. Meanwhile, the experiments are conducted to explore the new incorporation biotreatment technology of BA and immobilized anthanquinone as the alternative redox mediator to degrade azo dyes by halomonas sp. GTW.Strain GTW is an efficient azo dyes-degrading strain. It is identified as halomonas based on morphological and physiobiochemical characteristics and 16S rDNA sequence analysis. Strain GTW is deposited as a patent strain in China General Microorganism Culture with the accession number CGMCC1527.The characteristics of strain GTW growth and K-2BP degradation are investigated in order to lay a foundation for next experiments. Strain GTW is resistant to streptomycin/canamycin and sensitive to other antibiotics. Strain GTW can tolerate the concentration of 0.5-30% NaCl by the acclimatized procedure and decolorize the 13 selected dyes wastewater with high salt concentration in anaerobic conditions. The optimal conditions for both growth and degradation at 15% salt concentration are as follows: pH 7.2-7.5, temperature 30°C. Meanwhile, this work is conducted to study the decolorization of K-2BP by GTW at different NaCl and Na₂SO₄ concentrations, and the change characteristics of the oxidation-reduction potentials (ORP) with the decolorization of K-2BP at different mixed salt concentrations are also studied. The results suggest that GTW has a good ability to the decolorization of K-2BP at different mixed salt concentrations. And the ORP is elevated whenis added to the system. Furthermore, azo dyes are reduced by microorganisms only when the ORP values decrease the certain limits during the decolrization processes.The cleavage of the azo bond is the limited step of the mineralization processes because of the low oxidation-reduction potentials and complex structure. Then, the shuttling electrons from the biological oxidation of primary electron donors or from bulk electron donors to the electron-accepting azo dye is the controlled reaction of anaerobic azo dye reduction, which causes the proceeds relatively slow. However, this problem can be overcome by using the artificial redox mediator which speeds up the reaction rate. The experiments investigat the accelerating effect of BA and immobilized anthanquinone as a redox mediator in the bio-decolorization. It is observed that the artificial redox mediator BA and immobilized anthraquinbne are found to be extremely powerful catalysts, capable of raising the 1.5-2 fold reaction rate. The stabilized ORP values with BA and immobilized antbiaqumone are lower around -10--25 mV than the controls. It is also demonstrated that the addition of the BA and immobilized anthanquinone increased the reduction rates of all azo dyes tested. Therefore, the new inpOrporation bio-treatment technology of BA and immobilized anthanquinone as the alternative mediator with the salt-tolerant bacteria is a great improvement in the bio-treatment technology of dye wastewater.