The Interaction Effect Of Degradation Of Tannins And Dyes By White-rot Fungi

Aromatic tanning agents and dyes are the main components of refractory organics in tannery wastewater, which are widely used in the process of retanning and dyeing. The untreated wastewater is harmful to the environment because of the high chroma and poor biodegradability. The present treatment process is carried out by the combination of anaerobic digestion and aerobic degradation. However, the aromatic amine resulted from the anaerobic process and the tannery sludge produced at the end of the treatment put it into an awkward place. By contrast, White-rot fungi, which have broad-spectrum biodegradability and high degradation rate for aromatic compounds, show a great application prospect in the solo treatment of retanning and dying wastewater. But because of the complex components of the wastewater, it is need to clarify whether the degradation of the components have interactions in the reality.The degradability of four vegetable tannins which are Wattle, Quebracho, Betelnut and Chestnut by the white rot fungus WF1 was detected. The result showed that all tannins were degraded and the highest degradation rate was 46.433%. Chestnut’s degradability was better than the others, and the degradation rate and the concentration of vegetable tannins have a positive correlation.In order to determine the interaction effect of the degradation of vegetable tannins and dyes by white-rot fungi, the degradation of dyes and tannins by phanerochaete chrysosporium(GIM3.383) under the condition of co-substrates was studied. The result certified that there is an interaction between the two substrates on the degradation of the white rot fungus. The present of the vegetable tannins affected that the white-rot fungus synthesized and secreted lignin-degrading enzymes, and resulted in the difference on the fungal degradation of Basic fuchsin. The influence of the tannins on the dye degradation followed the sequence:Quebracho, Wattle and Chestnut. While dyes have inhibitory effect on the degradation of three vegetable tannins, the effect of dyes were enhanced with the increase of the dyes concentration. However, the inhibitory effect of dyes on the fungal degradation of vegetable tannins which are the easily degradable organics was smaller. In comparison to the azo dye, the triphenylmethane dyes have lesser influence on the tannin degradation. As for azo dyes, there is litter impact that the dyes with small molecular weight and short conjugated chain inhibit the degradation of vegetable tannins.In addition, the effect of structure of dyes on the fungal degradation of dyes and vegetable tannins was studied by QSPR. The ratio of the relative molecular mass and the number of sulfonic group:(MW/S), the number of polar group and non-polar group (I/O), and the number of azo functional group in dye molecules (-N=N-) were established, and there were good linear relation that the three structure indexes of the dyes affected the degradability of dyes and vegetable tannins. The (MW/S) and (-N=N-) have negative correlation with the degradability of dyes, while (I/O) has positive correlation. Moreover, the three structure indexes have negative correlation with the inhibitory effect of dyes on the degradation of tannins.Confirming the effect of the position and the number of hydroxyl in vegetable tannin molecules on the degradation of dyes, the degradation of dyes in the mediums with phenolic compounds was tested. The result showed that phenol had the promotion on the degradation of both triphenylmethane dyes and azo dyes. Phloroglucinol showed a promotion on the azo degradation, while pyrogallic acid showed a promotion on the degradation of triphenylmethane dye. Under condition that the initial concentrations of the phenolic compounds were 60mg/L, the compounds had the best promotion on the dye degradation.