The effect of molecular structure on the biodegradation of selected sulphonated phenylazonaphthol dyes by white rot fungus Pleurotus ostreatus
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The removal of water-soluble sulphonated azo dye effluents generated by textile industries is an important issue in wastewater treatment. Microbial treatment of environmental pollutants including dyes, with white rot fungi has received wide attention as a potential alternative for conventional methods in wastewater treatment. Eight sulphonated azo dyes with similar molecular structures were selected and degraded by the white rot fungus Pleurotus ostreatus. The decolorization effect was measured with a UV- spectrophotometer. Due to the different molecular structures of the dyes, the decolorization efficiency ranged from 70 percent to 90 percent after a 7-days treatment. Dyes with electron withdrawing group(s) on the benzene ring degraded quickly and had relatively high decolorization. Dyes with electron donating group(s) on the benzene ring had relatively lower decolorization. Dyes without functional group(s) on the benzene ring had relatively high decolorization even though they were less affected in the first three days. The solubility of dyes as well as the difference in the solubility parameter of the molecular units that are connected to the azo bonds, affects the decolorization. The more similar the solubility of the moieties, which connected to the azo bonds, the better the decolorization. Chemical instrumental analysis methods such as high performance liquid chromatography (HPLC) and capillary electropherosis combining with electrospray ionization mass spectrometry (CE-ESI-MS) were used to identify the degraded products and to develop a relationship between the chemical structures of the dyes and fungal decolorization. Fragmentation of several sulphonated dyes were investigated and fragmentation mechanisms of these breakdowns were proposed. The fragmentation supplied important information which was used to analyze the structure of the compounds. Several major degradation products were isolated and identified by HPLC and CE-ESI-MS, and the corresponding possible degradation pathways were proposed. In addition, in order to explain the degradation pathway, enzyme assays were performed. Characteristics such as enzyme activities and concentrations were determined and related to the effectiveness of decolorization.