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Decolourization kinetics of mixture of azo dyes under anaerobic conditionsтезисы доклада
- Авторы: Gladchenko M., Trukhina A., Kalyuzhnyi S.
- Сборник: In: Abstract book of Vth Intern. Conf. “Protection and restoration of the environment IX”
- Тезисы
- Год издания: 2008
- Место издания: Kefalonia, Greece
- Первая страница: 78
- Аннотация: The annual world market for dyes is estimated as 0.7-1.1 mln. tonnes while the Russian one – as only 0.023 million tonnes. 2% of dyes produced are discharged directly in aqueous effluent, and 10% are subsequently lost during the coloration process. A major class of all colorants used worldwide is represented by azo dyes – substituted aromatic moieties linked by azo groups (-N=N-). Presence of such compounds in the industrial wastewater may create serious environmental problems due to toxicity for aquatic life and mutagenecity and carcinogenicity to humans. As industrial dyes are designed to be chemically and photolytically stable, their spontaneous biodestruction by saprophite microflora in aerobic conditions occurs extremely slowly - till 50 years. Thus, there is a danger of accumulation of dyes in an environment. The most effective way of removal azodyes from wastewater is their biological treatment, particularly in anaerobic conditions, because the anaerobic microorganisms are capable to split these complex and toxic compounds. A variety of research can be found in literature devoted to kinetics of anaerobic conversion of individual azo dyes. However, the textile wastewater is usually a complex mixture of various azodyes that can influence an efficiency of their biological conversion. In literature, a degree of degradation of a mixture of dyes is usually monitored by a change of optical density at wavelength of a maximum of absorption of initial mixture. Such an approach is not completely correct because the investigated mixtures can contain dyes with very different maximal absorption wavelengths and with very different rates of decolourization of individual dyes. In this situation, the development of methods of quantitative estimation of kinetics of biodegradation of individual dyes in a mixture is rather actual problem. This paper firstly presents a simple spectrophotometric method of determination of concentrations of individual dyes in a mixture during their joint biodegradation. The simplest version of this method is based on measurements of optical densities only at maximal absorption wavelengths of individual dyes followed by resolution of the corresponding algebraic equations to find the concentrations of individual dyes in a mixture. The good accuracy of this method was confirmed by direct HPLC measurements of concentrations of individual azo dyes in a mixture. Using the developed method, the kinetics of anaerobic degradation of mixture of 2 azo dyes (Acid Orange 7 and Methyl Red) was studied under methanogenic conditions with addition of ethanol as an exogenic electron donor. It was found that though the decolourization process followed a first-order kinetics but the corresponding constants decreased with increasing dye concentrations (from 100 to 400 mg/l for each dye). This was caused by a toxic influence of azo dyes on anaerobic microorganisms generating reducing equivalents used for azo bond splitting. Moreover, it was found that Acid Orange 7 exerted a greater inhibitory effect on the decolorization of Methyl Red than vice versa. The pH–optimum for decolorization was in the neutral/slightly alkalinic range for both individual dyes and their mixture.
- Добавил в систему: Гладченко Марина Анатольевна