Thesis for Doctor of Philosophy

Nídia Dana Mariano Lourenço
“Azo dye biodegradation in Sequencing Batch Reactors”
Ph.D. Biotechnology, IST, 2003
Supervisor: H.M. Pinheiro

Abstract

Dyes represent one of the most problematic components of textile wastewaters since they are difficult to remove by the conventional treatment systems based on adsorption and aerobic biodegradation. Azo dyes can be reduced by bacteria under anaerobic conditions and the resulting aromatic amines can be aerobically degraded. In the present thesis the applicability of an anaerobic/aerobic Sequencing Batch Reactor (SBR) system was evaluated for the treatment of a simulated colored textile effluent containing an azo dye. Significant color removal of a monoazo and of a diazo reactive dye was obtained during the anaerobic reaction phase of SBR operation. The effect of different operational parameters on the decolorization of these two reactive dyes was studied, including the sludge retention time, the relative duration of the anaerobic and aerobic phases, the hydraulic retention time and the volumetric organic load. No aromatic amine mineralization occurred in the aerobic phase of the monoazo dye-fed SBR and none of the different approaches tested in order to promote this mineralization was effective. Abiotic decolorization tests were performed to evaluate the possibility of chemical dye reduction or adsorption in oxygen-depletion conditions. The decolorization of an acid monoazo dye in the same SBR was also attempted.

Keywords: textile wastewater; azo dyes; biological color removal; anaerobic azo bond reduction; sulfonated aromatic amines; aromatic amine mineralization