Removal of acid and direct dye by epichlorohydrin–dimethylamine: Flocculation performance and floc aggregation properties

Abstract

A cationic organic flocculant epichlorohydrin–dimethylamine (EPI–DMA) was employed for the treatment of acid and direct dye. The study aims at investigating the flocculation performance of EPI–DMA for the model dye, and corresponding floc aggregation properties, which were determined by jar test and photometric dispersion analysis, respectively. The interactions between cationic flocculant and anionic dye were investigated through spectra analysis. The results showed that EPI–DMA effectively decolorized the tested acid and direct dye. The viscosity and cationicity of EPI–DMA had different influence on the removal of different dye. Chemical interaction was observed between quaternary ammonium of EPI–DMA and sulfonic group of dye. The flocculation dynamic process showed that flocs with better aggregation and sedimentation properties were produced by EPI–DMA with higher viscosity and cationicity for acid dye. Contrarily, flocs with the best aggregation and sedimentation properties were produced by EPI–DMA with the lowest viscosity and cationicity for direct dye.

Introduction

Effluents from textile, printing, papermaking and food industries contain large quantities of dye compounds. The presence of dye in water can result in water environmental degradation, and even threaten human health due to the production of carcinogenic substances. Effective treatment process is needed to remove dye compounds from water and reduce the toxicity of effluents. The removal of dye by coagulation/flocculation is one of the most popular treatment processes (Allegre et al., 2004, Gao et al., 2007a, Gao et al., 2007b, Golob et al., 2005, Guibal and Roussy, 2007, Szygula et al., 2009). Different with the biological treatment, there is no toxic intermediate produced during the flocculation process of dyeing wastewater. Moreover, relatively high cost effectiveness ratio can be achieved during the large scale flocculation operation (Lee et al., 2006, Mo et al., 2007, Papić et al., 2004).

During the flocculation process, decolorization efficiency depends on the flocculant used and the treated dye. Different color removal efficiency is obtained by different flocculants for the same dye, and also different color removal efficiency is obtained by the same flocculant for different dyes.

Inorganic coagulant such as traditional aluminum and ferric salts, with a wide application in drinking water treatment, has limitations in removing some high-soluble and low molecular dyes (Joo et al., 2007, Kim et al., 2004, Shi et al., 2007). Organic polymeric flocculant has drawn increasing attention in various industries. Recently, the research and application of novel polymeric flocculant has been particularly active for the removal of dissolved and colloidal solids (Ovenden and Xiao, 2002, Sarika et al., 2005). Many organic polymers were synthesized and used as the flocculant to remove dye. Gao et al., 2007a, Gao et al., 2007b, Kang, 2007 employed polydimethyldiallylammonium chloride as the flocculant and found that high removal efficiency was achieved for treating reactive and disperse dyes. The copolymer of acrylamide and 2-[(methacryloyloxy)ethyl]trimethyl ammonium chloride was effective to removal reactive, acid and direct dyes from water under certain conditions (Shen et al., 2006). The organic flocculant used in this study, epichlorohydrin–dimethylamine (EPI–DMA) polymer, is a poly-quaternary polymer produced by the reaction of dimethylamine and epichlorohydrin. Similar polymer prepared from ethylenediamine and epichlorohydrin was used in removing nitrite ions by Bíçak and Şenkal (1998). Recently, EPI–DMA was employed as the flocculant. The decolorization performance of EPI–DMA has been studied for reactive and disperse dyes in our previous research. In this study, Acid Cyanine 5R and Direct Violet N dyes were chosen as the model dye compounds.

The flocculation process can be explored by analyzing floc aggregation properties. Flocs are formed after the addition of flocculant, and floc size increases due to aggregation. A steady state of floc size occurs eventually due to the equilibrium between floc aggregation and breakage. All the floc aggregation rate and floc size can be used to compare flocculation effectiveness.

The main objectives of this study were to investigate the performance of EPI–DMA with different intrinsic viscosity and cationicity in the flocculation of acid and direct dyes, to investigate the floc aggregation properties of these EPI–DMA flocculants, and to explore the relationship between flocculation mechanisms and properties of flocculant.