Thesis for Master of Science

Maria da Graça Ejarque Albuquerque
“Efeitos da redução biológica de sulfato e de mediadores redox na descoloração de corantes azo em bio-reactores descontínuos sequenciais”
M.Sc. Biotechnology, IST, 2004
Supervisor: H.M. Pinheiro

Abstract

Azo dyes are a major class of synthetic dyes extensively discharged in wastewater throughout Europe . The reductive cleavage of the azo bond of azo dyes in anaerobic treatment bioreactors has been repeatedly reported. However, the resulting amine metabolits have been found to be recalcitrant under anaerobic conditions. In this work, an anaerobic-aerobic sequencing batch reactor was found to allow such transformation, with the added possibility of metabolite mineralization in the aerobic period. 1-l reactors were operated in 24-h cycles comprising anaerobic and aerobic reaction phases, feed with a simulated textile effluent including a reactive type (Remazol Brilliant Violet 5R) or an acid type (Acid Orange 7) azo dye. The aim of the presently reported experiments was to access the role of biological sulphate reduction in the anaerobic decolourisation process. Selective inhibition of sulphate reducing bacteria was carried out in the sulphate-containing, reactive dye fed reactor, whereas the acid dye fed reactor was supplemented with sulphate and other redox mediators, namely quinines, in order to promote electron transfer to the azo bond. Bio-augmentation of the latter reactor with a pure strain known to decoulorise azo dyes, Desulfovibrio alaskensis, was also carried out. A chemically mediated reduction of the azo bond coupled to biological sulphate reduction seems to account for the high decoulorisation yields observed in both dye fed reactors.

Keywords: Azo dyes, decolourisation, Sequencing Batch Reactors, biological sulphate reduction, redox mediators