The discharge of highly coloured wastewater into the ecosystem involves environmental problems. It is detected a widespread contamination of soil as well as ground and surface water by synthetic dyes used for textile dyeing/finishing and also in food, paper and cosmetic industries. Most of these compounds are toxic, mutagenic or at least cause an aesthetic problem in receiving water and soil [1]. Approximately 15% of total world production of wastewater, or 150 tons per day, is estimated to be released into the environment without proper treatment [2].

Several methods are being used to decolourize dye wastewater. Each method has advantages and disadvantages. Biological processes show a limited colour removal due to the toxic nature of some dyes and the high salt concentration. Adsorption in activated carbon, membrane filtration, coagulation-flocculation and chemical oxidation with ozone have a considerable cost. Thus, there is a great need to develop an economic and effective way of removing synthetic dyes from wastewater at the level of the industry itself in the face of the ever-increasing production activities.

In the recent years, there has been a large interest in the use of electrooxidation process. Among them, sonoelectrolysis treatment is an attractive method. In this treatment, electrolysis and sonolysis are combined. In this work, in order to test the feasibility of the method purposed, a comparative study was carried out on the decolourization of dyes from a leather factory using electrolysis treatment alone and sonoelectrolysis.

For this study, electrolysis of several dyes (Trupocor Red, Reactive Black 5, Lissamine Green, Methyl Orange and Acid Black 24) was carried out in an electrochemical cell of 40ml working volume in absence or presence of ultrasound. All experiments were conducted at constant voltage drop (5 V) applied through a couple of graphite electrodes. The equipment used for experiments with ultrasound was Sonoplus HD2070 (20 kHz cycle 10%, power 60%). The effect of ultrasound on the dye degradation was study by immersion of the microtip into the electrochemical cell. Samples of the reaction solutions were removed from the electrochemical cell and were analysed for pH and dye concentration. Residual dye concentration was measured spectrophotometrically at the maximum visible wavelength of each dye. The decolourization was determined following the decrease in the absorbance at the same wavelength and expressed in terms of percentage [3].

According to the results obtained in the present work, the superiority of sonoelectrolysis treatment over electrolysis has been demonstrated. The application of ultrasound in electrochemistry process permits the degassing and continuous activation of the electrode surface. Moreover, the addition of electrolytes such as Na₂SO₄ improved the efficiency of the sonoelectrolysis process (Figure 1). All experimental results indicate the suitability of sonoelectrolysis process for its application to dye degradation.

Acknowledgements

This research was funded by Xunta de Galicia (Project PGIDIT04TAM314003PR).

References

[1] A Aguedach, S Brosillon, J Morvanb, K Lhadi. Applied Catalysis B: Environmental 57 (2005) 55-62.

[2] C. Maynard, Handbook of Industrial Chemistry, Van Nostrand Publ.,New York, 1983.

[3] M.A. Sanroman, M. Pazos, M.T. Ricart, C. Cameselle, Chemosphere 57 (2004) 233.

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1. Sono-enzymatic coloration of wool
2. High-Energy Micro-Environments Applications in Textiles (HEMEAT)