Decolorization of the textile dyes Reactive Red 2 and Reactive Blue 4 using Bjerkandera sp. Strain BOL 13 in a continuous rotating biological contactor reactor

Abstract

The decolorization of two different textile dyes, Reactive Red 2 and Reactive Blue 4, was studied in batch as well as continuous experiments using Bjerkandera sp. Strain BOL 13. The batch experiments were performed to study the decolorization of the dyes separately as well as in a mixture. The results from the experiments showed that the fungus decolorized both dyes. The absorbance was measured at 538 and 595 nm, the peak absorbance wavelengths of the red and blue dyes respectively. The absorbance decreased with 99% at both 538 and 595 nm in the experiments in which the dyes were studied separately at a concentration of 100 mg/l. The corresponding figure for the experiment in which the dyes were studied in a mixture was 98%. A continuous rotating biological contactor was then used to study the decolorization of mixtures of the two dyes at three different concentrations, e.g. 50, 100 and 200 mg/l of each of the dyestuff. The decrease in absorbance at 538 nm was 96% at the two lower dye concentrations while it was 81% at the highest concentration. The corresponding figures at 595 nm were 94 and 80%. The hydraulic retention time was 3 days. Scanning of the absorbance between 200 and 800 nm showed that three peaks disappeared in the UV range during treatment (246, 283 and 323.5 nm) and that a new plateau was formed around 270 nm.

Introduction

Wastewater from textile industries is a problem in large parts of the world. The degradation products of textile dyes are often carcinogenic. Furthermore, the absorption of light due to textile dyes creates problems to photosynthetic aquatic plants and algae [1], [2].

Reactive dyes are highly water-soluble polyaromatic molecules. The three most common groups are azo, anthraquinone and phthalocyanine dyes. They react with nucleophilic groups on the fabric forming covalent bonds, which gives a good fixation. Despite this, 10–50% of the dye will end up in the effluent because the dye molecule might react with hydroxyl ions in the solution, giving rise to even more water-soluble hydrolysed molecules [3]. Furthermore, the dye preparations are not homogenous. A range of different by-products, some of which are colored, will contribute to the pollution. Reactive dyes have been shown to pass ordinary aerobic sewage treatment unaffected [3], [4]. Some dyes are decolorized under anaerobic conditions however the effluent might be toxic [5], [6]. Furthermore, colorization was found to take place if the effluent is left untreated for a long period of time, in a study performed by Knapp and Newby [7]. Similar results were obtained during the present study when a continuous reactor with anaerobic microorganisms was used for the degradation of Reactive Blue 4 (unpublished data).

White rot fungi have also been used for the degradation of different dyes [8], [9], [10], [11], [12], [13], [14]. An advantage with these organisms is that they produce and excrete ligninolytic enzymes that are non-specific with regard to aromatic structure. This means that they are capable of degrading mixtures of aromatic compounds [12]. Most studies concerning degradation of dyes have however been preformed with one dye at a time. The most commonly used strains in regard to degradation of textile dyes are Phanerochaete chrysosporium and Coriolus versicolor [10], [12].

The aim of the study was to examine the metabolic potential of Bjerkandera sp. Strain BOL 13 regarding decolorization of a mixture of two representative dyes from two of the most commonly used groups of reactive dyes, Fig. 1, in a continuous reactor. A system with immobilised mycelia was used since results from an earlier study indicates that enzyme secretion is better in this kind of systems than in systems built on suspended cultures [15]. C. versicolor has furthermore been shown to efficiently decolorize Everzol Turquoise Blue G, a phthalocyanine dye, when a rotating biological contactor was used in batch mode [12].