Thesis for Doctor of Philosophy
“Desenvolvimento de um sistema de biodegração óxico-anóxico para águas
residuais têxteis”
Ph.D. Biotechnology, IST, 2006
Supervisor: H.M. Pinheiro
Abstract
The presence of dyes is a serious problem of wastewaters from the textile industry, since they are generally recalcitrant in the conventional biological units of wastewater treatment plants. Azo dyes are however susceptible to biodecolourisation in oxygen-depleted conditions. The present work explores a way of implementing such conditions, by anoxic incubation of biomass wasted from an activated sludge reactor with a simulated, dye-containing effluent. The effect of different parameters in the biomass production reactor (hydraulic and aeration regimes, fed carbon source type and organic load, sludge age, temperature) on decolourisation kinetics for two azo dyes (acid and reactive) was examined. Significant effects were observed for all tested parameters. A chemometric analysis of the results was undertaken, highlighting the main factors. The anoxic decolourisation process was also followed in terms of organic carbon conversion and cell viability evolution, and a mechanistic model is proposed for its description. In paralel, decolourisation of the same feed was tested in a methanogenic reactor and the perfomance of the two systems was compared. Since dye decolourisation did not lead to mineralisation, a polishing treatment through electrochemical oxidation was also tested, with high efficiency.
Keywords:
textile
wastewater; azo dyes; biological color removal; anaerobic azo bond reduction;
sulfonated aromatic amines; aromatic amine mineralization