Decolorisation of disperse dark blue 148 with ozone

The aim of this study is decolorisation of CI Disperse Dark Blue 148 dye by ozone treatment which is one of the most attractive alternatives for solving the problem of color in textile dyeing effluents. A venturi injection system added dyeing chamber for getting ozone from the ozone generator. And additive (acetic acid and dispersing agent) put in the dyeing. After the coloration, the experimental color, chemical oxygen demand (COD), pH, temperature (°C) and conductivity (μS/cm) were measured. The results encourage the use of the system for decolorisation trials as well as dyebath effluent recycling.


Introduction
Dyes and pigments have been used for coloring in the textile industry for many years [1,2]. Disperse dyes are the most important dyes also used in dyeing PET fibers. [3] The wastewater from textile dyeing typically contains high concentrations of colorants, effective decolorization methods are urgently required [2]. Wastewater discharge is extremely variable in composition, exhibiting strong colour, fluctuating pH, and significant COD loads [4]. Many techniques able to remove colour are listed in the literature, such as coagulation-flocculation, adsorption and membrane filtration, have been used to decolorize textile effluents, these techniques suffer disadvantages of sludge generation, adsorbent regeneration and membrane fouling. Oxidation is one of the potential alternatives to decolorize and to reduce recalcitrant wastewater loads from textile dyeing and finishing effluents [3][4][5] Because of O3 is an unstable molecule and rapidly decomposes to O2 that is capable of participating in many chemical reaction with inorganic and organic substances [3][4][5][6][7]

Materials and Method
In this study, CI Disperse Dark Blue 148 disperse dye was used at 0,1 g/l. The molecular structure of dye as shown Figure 1. The dye solutions were prepared either by using dye alone or by using dye and additives together. The dyeing additives were 1 ml/ l acetic acid and 1 ml/l dispersing agent. A Prodozon PRO DO25 model ozone generator (Ankara, Turkey) with a maximum ozone generation capacity of 25 g/h was used during the experiments. Ozone gas flow rate was adjusted to 5 g/h ozone was fed through a venture injector placed on the liquor circulation pipe of a Atac BB01F sample dyeing machine (Atac Co., Istanbul, Turkey). All connections were made by teflon tubing lines. The total amount of the treated liquor was 10 liters. The treatment time was extended to 20 min by 2,5 min steps. The ozone integrated system is given on Figure 2.

Results and Discussion
The measurement value of the reference (untreated dyestuff solution) and the samples (different ozonation time and dyeing process with additives) were summarized in Table 1 and Table 2.
The effect of ozonation time and dyeing additives on the temperature, pH, conductivity, color absorbance and COD of the dyeing water were investigated. As it was expected, when the ozonation time was increased; the measurement value of the temperature and conductivity were increased, pH value was decreased. This results were seen dyeing process with additives at the same time. Figure 3 shows the photo of the color change during ozone treatment. The colored water rapidly becomes clear after ozone treatment.   Figure 5 shows the COD values. The solutions of 0.1 g/l disperse dye with and without additives (acetic acid and dispersing agent) made a quite difference COD value all the ozone treatment time. It is originated from the using additives (acetic acid and dispersing agent) with dyeing. As it is known. using chemical makes the solution worse about the COD values.

Conclusion
This pilot-scale study investigated a venturi injection system added the dyeing chamber for getting ozone from the ozone generator. This system to the decolorisation of disperse dark blue 148 was achieved successfully either in presence of dyeing additives or not. The rapid decolorisation effect of ozone is reported before in the literature mostly by using a diffuser to feed ozone into the reaction chamber [8][9][10]. However. in this study. trials were performed on ozone feeding integrated sample dyeing machine. Hence a venturi injection system was equipped rather than diffusers. The results encourage the use of the system for decolorisation trials as well as dyebath effluent recycling.