Sixteen sulfonated and unsulfonated azo dyes as well as eleven sulfonated and unsulfonated aromatic amines were analyzed and qualitatively characterized by means of pyrolysis gas chromatography/mass spectrometry at different temperatures. Aniline and aminonaphthalene were found to be the dominant pyrolysis products of sulfonated aromatic amines and dyes. Azo dye and dye class specific key compounds such as benzidine, vinyl-p-base and 4-aminoazobenzene could be identified by pyrolysis gas chromatography/mass spectrometry of commercial acid, cationic, direct, reactive and solvent dyes. 500 degrees C was the optimal pyrolysis temperature for most of the pyrolyzed compounds. The method was applied to a dried sample of a textile wastewater concentrate from a dyeing process. Reactive azo dyes of the group of Remazol dyes and anthraquinone dyes could be identified as the major compounds of the sample. The finding of caprolactam (a printing additive) suggests that the wastewater contained effluent from a process of heat-activated printing with reactive dyes. p-Chloraniline, a banned aromatic amine, was identified. Chemical reduction of the wastewater sample prior to pyrolysis resulted in the release of volatile aromatic amines and aided the classification of several products of pyrolysis.
A biological high-performance treatment process comprising two 40-L reactor compartments has been developed for purification and decoloration of concentrated textile wastewater containing up to 15 g L(-1) reactive dyestuff. The decoloration rate of 95% meets the requirements of German legislation for textile wastewater treatment. Successful process development and optimization was achieved by use of high-performance liquid chromatography, with diode-array and electrospray tandem mass spectrometric (LC-ESI-MS-MS) detection, coupled with inline microfiltration membrane-sampling devices, applied online to bioreactors as a process analytical tool for the first time. The optimum process performance was found by correlation of dye and decoloration product-specific concentrations with summary properties such as redox potential and dissolved oxygen content. Details of the degradation and decoloration mechanism for the azo dye reactive black 5 was revealed by using mass spectrometry for structure elucidation.
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