Decolorization Of Dye Wastewater With High Salt Concentration By The Acclimatized Salt-tolerant Cultures

Hyper-salinity coloured wastewater is a consequence product of batch processes both in the dye manufacturing industries and in the dye-consuming industries, and the salt concentration is up to 15 % - 20 %. And hyper-salinity usually causes plasmolysis and/or loss of activity of cells, therefore, some traditional aerobic- and anaerobic-biological treatments result in low decolorization and BOD removal. In this paper, the experiments were conducted to explore the method of acclimatization of salt-tolerant culture and investigate decolorization of different concentrations of azo dye by salt-tolerant bacteria under anaerobic conditions and different concentrations of NaCl.Three salt-tolerant mixed cultures (AS, SW, TAS) were acclimatized by the gradually increasing NaCl concentration and these acclimatized cultures could decolorize the 13 simulated dye wastewater with high salt concentration. The effects of salt concentration and dye concentration on decolorization rate were compared. With the elevated concentrations of salt and dye, the decolorization was lower. The abilities of decolorization by three mixed cultures to some of dyes were studied. In terms of decolorization and growth in high concentration of NaCl, AS and SW mixed cultures were more suitable for the treatment of hyper-salinity colored wastewater than TAS mixed cultures, hi addition, it was investigated that six carbon sources (yeast extract, peptone, sucrose, glucose and so on) effected on the declorization rate. And more, the results show that the maximal decolorizetion dye concentration is up to 2000ppm and the most suitable pH is 7.0 to 7.2.At the same time, this work was conducted to study the changing characteristics of the oxidation-reduction potentials (ORP) during the processes of the biological decolorization of azo dyes, knowledge of which will be useful for prediction of the decolorization capacity of oxidative and reductive biocatalysts. Reduction of these azo dyes did not occur under aeration conditions, and azo dyes are reduced by microorganisms only when the Oxidation-Reduction Potential (ORP) values decrease the certain limits (<-100 raV) during the decolrization processes. The results with the salt-tolerant mixed culture indicate that the reduction of azo dyes may be influenced by the chemical nature of the azo compound and redox mediators.