Nonionic microemulsion systems applied for removal of ionic dyes mixtures from textile industry wastewaters

Highlights

• Innovative microemulsion system for removal of ionic dyes mixtures from wastewaters.

• Efficient, low cost and easy to use method for dye extraction.

• The possibility to implement the method in a scale-up water treatment plant.

Abstract

Pollution abatement of wastewaters discharged from textile industry remained a serious environmental problem susceptible for further technological improvements. This study proposes an innovative, fast and efficient microemulsion system for removal of ionic dyes mixture from such wastewaters.

A series of physical–chemical parameters (initial dye concentration, pH, salt and sequestrant concentrations) with significant influence on the dye removal efficiency of water/nonionic surfactant/ethyl acetate ternary system has been studied in order to find out the optimal compositions for an efficient extraction of cationic and anionic dyes from aqueous media. The optimum extraction conditions for this system correspond to pH > 5, surfactant concentration around 8% (w/w) and organic phase concentration around 13% (w/w), resulting in extraction efficiencies around 90%. By adding sodium chloride (concentration > 60 g/L) in the ternary system the removal efficiency was improved.

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.