The Degradation Characteristics Of Shewanella Oneidensis MR-1 And Biosorption Mechanism Of Fungi For Classical Dyes

The dye and textile industries are booming and important for economic growth in China, but the pollutants cased by these industries are crucial problems we should not ignore for sustainable development. More than 80% dyes having azo bond and aromatic structure are of chemical stability, carcinogenicity, teratogenicity and mutagenesis. Therefore, to find effective microorganisms having biosorption and/or biodegradation capabilities for dyes are received more and more attention from environmental scientists. In this study, the decolorization characteristics of Shewanella oneidensis MR-1 and adsorption behavior of fungal biosorbents for dyes were investigated. The main results are as follows:(1) Decolorization and azoreductase characteristics of Shewanella oneidensis MR-1Shewanella oneidensis MR-1 was found to reach 99.36% and 78.25% decolorization for Methyl Orange and Acid Yellow 199 in solutions, respectively. The suitable pH range for decolorization of Methyl Orange and Acid Yellow 199 by S. oneidensis MR-1 was 4.0-7.0 and 6.0-8.0, respectively The azo dyes removal by S. oneidensis MR-1 was slightly enhanced by addition of Mg2+, but inhibited by Pb2+, Cd2+, Cu2+, Fe3+and Fe2+. The enzyme activities of NADH-DCIP reductase and azoreductase were 2.67 and 3.0 times higher, and 1.92 and 2.48 times higher, respectively in the Methyl Orange treatment and in the Acid Yellow 199 treatment as compared to the control treatment. These findings indicated that the azo dyes decolorization by S. oneidensis MR-1 was via reduction mechanism. The azoreductase was found to reach maximum enzyme velocity 220.59 U/mg, while no enzyme activities were found for the putative azoreductase toward Methyl Red. Azoreductase had highest specific activity (153.16 U/mg) at pH 6.5, which also showed a preference for NADH compared to NADPH as electron donor.(2) Biosorption mechanism of fungi for dyesMaximum biosorption capacities of 225.38 and 411.53 mg g"1 under initial dye concentration of 800 mg L-1, pH 3.0 and 40℃conditions were observed for Acid Black 5 (AB) and Congo Red (CR) for Penicillium YW 01, respectively. The Weber-Morris model analysis indicated that intraparticle diffusion was the limiting step for biosorption of AB and CR onto biosorbent. Analysis based on the artificial neural network and genetic algorithms hybrid model indicated that initial dye concentration and temperature appeared to be the most influential parameters for biosorption process of AB and CR onto biosorbent, respectively. The values of initial biosorption rate of biosorbent in phosphoric-phosphate buffer were found to be higher than that of corresponding values in aqueous solution, indicating phosphoric-phosphate buffer enhanced the initial biosorption rate of biosorption process. Weber-Morris model analysis indicated that the boundary layer effect had more influence on the biosorption process in phosphoric-phosphate buffer.In single system, the biosorption capacities of CDAB-modified biosorbent reached 160.36 and 280.39 mg g-1 for Acid Blue 25 (AB 25) and Acid Red 337 (AR) 337, respectively, which were 1.52 and 1.66 times higher than that of unmodified biosorbent. In binary system, the biosorption capacities of unmodified and CDAB-modified biosorbents for both dyes decreased significantly compared to that in single system. Relative competitiveness analysis demonstrated that there existed critical initial concentration ratio which determined the predominance of dyes during biosorption process. The biosorption of AB 25 was found to be in dominant position at initial concentration ratio of [AB 25]/[AR 337] above 0.63. Sensitivity analysis of the factors affecting biosorption examined by an artificial neural network model showed that pH was the most important parameter, explaining 22%, followed by nitrogen content (16%), initial dye concentration (15%) and carbon content (10%). The biosorption capacities were not proportional to surface areas of the sorbents, but were instead influenced by their surface chemical characteristics. The data further suggest that differences in carbon and nitrogen contents may be used as a selection index for identifying effective biosorbents.