Nonionic microemulsion systems applied for removal of ionic dyes mixtures from textile industry wastewaters
Introduction
The removal of color from dyehouse wastewater is currently one of the major problems faced by the textile industry [1], [2], [3], [4]. The textile dyeing and finishing industry has created a huge pollution problem as it is one of the most chemically intensive industries on earth, and the principal polluter of clean water (after agriculture). The daily water consumption of an average sized textile mill having a production of about 8000 kg of fabric per day is about 1.6 million liters [5]. The stability and resistance of dyes to degradation has made color removal from textile wastewater difficult by conventional biological treatment plants and considerable research is focused on addressing this problem [1], [6]. Among various new techniques used for color removal, extraction by microemulsion has been introduced as an innovative and very efficient method [1], [7], [8].
Microemulsions have a wide variety of applications ranging from oil recovery to food, cosmetics, biotechnology, detergency, nanomaterials synthesis and environmental remediation [9], [10], [11], [12], [13], [14]. Microemulsions are optically isotropic and thermodynamically stable colloidal systems in which water and oil may coexist in a single phase by the addition of a surfactant with an appropriate hydrophile-lipophile balance [15]. Microemulsion extraction systems offer several advantages compared to the conventional solvent extraction such as: efficiency, enhanced selectivity, no need of processing at high temperature or pressure, cost effective and less time consuming.
A detailed study has been carried out in this paper to determine the best composition and the optimal conditions for dye removal from textile wastewaters using the extraction in microemulsion systems. Anionic dye Methyl Orange and cationic dyes Crystal Violet and Rhodamine B, respectively, as being largely present in the dyeing process and rinsing effluents of the textile industries were selected as being representative for this study [16], [17], [18], [19]. The surfactant was chosen from nonionic class (polyoxyethylene (4) lauryl ether) and the organic phase required to form the microemulsion system was ethyl acetate. Nonionic surfactant was used since it has a low toxicity and exhibits better solubility properties in microemulsion systems [20]. Moreover, nonionic surfactants have the ability to form microemulsion without the assistance of co-surfactant. Ethyl acetate has several advantages: it is manufactured on a large scale for use as a solvent; it is very volatile so it can be removed from a sample by heating; its LD50 for rats is 11.3 g/kg, indicating low toxicity.
In the present work the extraction in microemulsion technique has been used in order to remove mixture of dyes from textile wastewaters. In order to simulate the practical working conditions of a water treatment plant, the effect of several factors on removal efficiency was studied: initial dye concentration, pH, inorganic and organic compounds concentrations. To the best of our knowledge, no study has been reported on the use of nonionic microemulsions for color removal of a mixed dyes solution composed by ionic dyes. Moreover, the nonionic microemulsions are able to reduce the level of pollutants from wastewaters with the purpose of reaching the standards established by the environmental regulations in a very short time with the possibility to reuse the cleaned water in the industrial circuit without additional treatment steps.
Section snippets
Materials
Ethyl acetate (EtOAc) 99.8%, Rhodamine B (Rh B) dye, sodium hydroxide (NaOH), sodium chloride (NaCl) and hydrochloric acid (HCl) were purchased from Sigma–Aldrich. Crystal Violet (CV) and Methyl Orange (MO) dyes were obtained from Riedel-de Haen and ethylenediaminetetraacetic acid (EDTA) was bought from Fluka. Polyoxyethylene (4) lauryl ether (Brij 30) and polyethylene glycol tert-octylphenyl ether (TX-114) were provided by Acros Organics. Distilled water was used for the preparation of the
The selection of optimal extraction composition
The specific characteristics of physical and chemical equilibria involved in the dyes removal by extraction procedure from aqueous media using WII microemulsions in Water/Brij 30/EtOAc system have been evaluated. The aqueous phase is represented by the pollutant sample to be treated, which is mixed with the oil phase represented by ethyl acetate, and surfactant as Brij 30. Using the ternary phase diagrams described in a previous paper [7], different composition points were chosen from the WII
Conclusions
The results demonstrate that the extraction process follows the microemulsion mechanism. The micelles that are initially in the aqueous phase are transferred into the organic phase and turned into W/O microemulsion corresponding to a Winsor II system.
The Water/Brij 30/Ethyl Acetate microemulsions were very efficient in dye removal with over 90% efficiency for 25 mg/L dye concentration. The basic pH favoured the color extraction in the studied microemulsion system which underlines the
Acknowledgements
The work has been funded by the Sectorial Operational Program Human Resources Development 2007–2013 of the Ministry of European Funds through the Financial Agreement POSDRU/159/1.5/S/134398.
Also we want to thank to the financial support provided by the project CHALK-RESTORE, PN-II-PT-PCCA-2011-3.2-1640, contract no. 222/2012.
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