Thesis for Master of Science

Manuela Cristina Paulo Carvalho
“Descoloração de corantes têxteis com lamas biológicas”
M. Sc. Biotechnology, IST, 1999
Supervisor: H.M. Pinheiro

Abstract

In this work, the use of an aerobically-grown mixed microbial culture (activated sludge) for anoxic decolourization of textile dyes was studied. Three reactive dyes of the vinyl-sulphone type were tested, with azo/copper-complex, di-azo and anthraquinone chromophores. Culture grow and decolourization runs used a synthetic medium with a hidrolysed starch derivative (additive in the cotton textile industry) as the carbon and energy source. Decolourization tests were performed in closed, agitated vessels, at 20ºC, after deaeration by sparging with N2. The studied parameters were the availability of oxygen, the addition of redox agents (sulphide, sulphate), the biomass (2.5 – 12.5 dry weight/L) and carbon source (4-500 mg/L) concentrations, the dye type and concentration (0.1 – 2.0 g/L) and the medium pH (6 – 9). Biological decolourization was observed with all the tested dyes, with rates apparently limited by dye concentration. The addition of sulphate and a carbon source above 12 mg/L had no effect on decolourization rates. With the copper-complex dye, results indicated a competition between the azo-bond and the metal ion for the microbial reducing equivalents. Observed results pointed also to a non-enzymatic, extracellular decolourization mechanism, mediated by electron carriers.

Keywords: Textile effluent, reactive dyes, activated sludge, decolourisation, anoxic conditions, azo bond