Elsevier

Water Research

Volume 36, Issue 5, March 2002, Pages 1143-1154
Water Research

Advanced oxidation of a reactive dyebath effluent: comparison of O3, H2O2/UV-C and TiO2/UV-A processes

https://doi.org/10.1016/S0043-1354(01)00335-9Get rights and content

Abstract

In the present study the treatment efficiency of different AOPs (O3/OH, H2O2/UV-C and TiO2/UV-A) were compared for the oxidation of simulated reactive dyebath effluent containing a mixture of monochlorotriazine type reactive dyes and various dye auxiliary chemicals at typical concentrations encountered in exhausted reactive dyebath liquors. A525 (color), UV280 (aromaticity) and TOC removal rates were assessed to screen the most appropriate oxidative process in terms of reactive dyebath effluent treatment. Special emphasis was laid on the effect of reaction pH and applied oxidant (O3, H2O2) dose on the observed reaction kinetics. It was established that the investigated AOPs were negatively affected by the Na2CO3 content (=867 mg/L) which is always present at high concentrations in dyehouse effluents since it is applied as a pH buffer and dye fixation agent during the reactive dyeing process. The ozonation reaction exhibited almost instantaneous decolorization kinetics and a reasonable TOC reduction rate. It appeared to be stable under the investigated advanced oxidation conditions and outranked the other studied AOPs based on the above mentioned criteria. Besides, the electrical energy requirements based on the EE/O parameter (the electrical energy required per order of pollutant removal in 1 m3 wastewater) was calculated for the homogenous AOPs in terms of decolorization kinetics. In view of the electrical energy efficiency, ozonation and H2O2/UV-C oxidation at the selected treatment conditions appear to be promising candidates for full-scale dyehouse effluent decolorization.

Introduction

Like many other industrial effluents, textile industry wastewater varies significantly in quantity, but additionally in composition [1]. Textile wastewater is strongly colored which creates an environmental as well as aesthetic problem. As regulations are becoming ever more stringent, the need for technically and economically more efficient means of decolorization and mineralization is obvious. Currently, there are no economically attractive technologies to achieve color removal. Existing physicochemical technologies such as membrane filtration or activated carbon adsorption are expensive and commercially unattractive. Furthermore, these processes just transfer pollutants from one phase to another rather than eliminating them from the water matrix. Recovery and reuse of certain chemical compounds present in dyebath effluents is currently under investigation [2], [3] but is not possible for the application of certain dyestuff classes, such as reactive dyes. In addition, the problem of color in dyehouse effluent has become identified particularly with the dyeing of cotton fibers that contributes to almost 40% of total fiber consumption annually worldwide, and the use of reactive dyestuffs since as much as 50% of these dyes end up in the exhausted dyebath in their hydrolyzed and unfixed form [4], [5].

The chemical limitations of conventional chemical oxidation techniques can be overcome by the development of so-called advanced oxidation processes (AOPs) which use strong oxidizing agents (O3, H2O2) and/or catalysts (Fe, Mn, TiO2) in the presence or absence of an irradiation source [6]. AOPs mainly involve the generation of a very powerful and non-selective oxidizing agent, the hydroxyl radical (OHradical dot), for the destruction of refractory and hazardous pollutants found in groundwater, surface water and industrial wastewater [7].

The treatment of reactive dyes in aqueous solutions via different AOPs has been extensively studied [8], [9], [10], [11], [12], [13], [14], [15]. However, the advanced oxidation of reactive dyebath effluents is rather limited to a few investigations [16], [17], [18]. From these studies it could be inferred that the dyebath constituents (sodium salts, detergents, wetting agents, sequestering agents etc.) seriously reduced the treatment efficiency of the selected AOP. Thus, the inhibiting effect of common reactive dye auxiliary chemicals, in particularly the OHradical dot scavenging effect of carbonate ions applied in the form of anhydrous Na2CO3 and used at substantially high concentrations in the reactive dyeing process, still needs to be further questioned for different AOPs. Moreover, a detailed assessment of the advanced oxidation conditions (i.e. reaction pH and oxidant dose) that are AOP- and pollutant-specific has to be undertaken to determine the most appropriate AOP for the treatment of the textile effluent in question.

With the aim to contribute to the clarification of the above mentioned points, the experimental work described herein evaluates comparatively the treatment of simulated exhausted reactive dyebath liquors prepared from a mixture of different dyeing formulations by two homogenous (O3, H2O2/UV-C) AOPs and one heterogeneous (TiO2/UV-A) AOP in batch experiments. Optimization of the reaction pH and oxidant (O3 and H2O2) dose were made in accordance with the highest rate in color (absorbance at 525 nm wavelength), aromaticity (absorbance at 280 nm wavelength) and TOC (total organic carbon) removal. Thereafter, the oxidative performance of the selected chemical oxidation systems was compared in terms of their electrical energy requirements.

Section snippets

Simulated reactive dyebath effluent

The investigated reactive dyes and dye assisting chemicals were kindly supplied by an integrated textile manufacturing plant. Synthetic spent dyebath wastewater was prepared weekly according to the cotton fiber dyeing procedure of the factory. The recipe mixture was used considering the international market share of their reactive dyestuff content and colors mostly applied to the cotton fabrics in the dyeing stage. The synthetic reactive dyebath effluent was prepared according to the

General aspects

Changes in pH were rather insignificant during any advanced oxidation of the simulated dyehouse effluent, which is easily explained since the reactive dyebath effluent was highly buffered. In all treatment cases, disappearance of UV-VIS absorbance exhibited a first order kinetic behavior, whereas no clear kinetic trend was observed for the TOC abatement rates.

O3 treatment

Ozone reacts with aromatic pollutants found in water and wastewater via two different pathways namely direct molecular and indirect

Conclusions

The comparison of different OHradical dot generation techniques is of interest, on the one hand, to determine the most efficient experimental conditions for the destruction of organic pollutants present in dyehouse effluents, and, on the other hand, to provide useful information for the understanding of the mechanism of advanced oxidation processes. The following conclusions can be drawn from the experimental work:

  • Among the investigated AOPs, the quickest color (rid=11.8 1/m×min), UV280 (kUV280=0.35 1/min)

Acknowledgements

Idil Arslan is grateful to TUBITAK BAYG for the NATO A2 scholarship. The authors also acknowledge Bogaziçi Research Foundation for the financial support through grant 98Y-03.

References (31)

  • V.M. Correia et al.

    Characterization of textile wastewater—a review

    Environ Technol

    (1994)
  • P. Grau

    Textile industry wastewaters treatment

    Water Sci Technol

    (1991)
  • J.R. Easton

    Color in dyehouse effluent

  • A. Reife et al.

    Environmental chemistry of dyes and pigments

    (1996)
  • O. Legrini et al.

    Photochemical processes

    Chem Rev

    (1993)
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