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Ultrasonics Sonochemistry xxx (2013) xxx–xxx

Contents lists available at ScienceDirect Ultrasonics Sonochemistry journal homepage:

Sonochemical and hydrodynamic cavitation reactors for laccase/hydro- gen peroxide cotton bleaching q

Idalina Gonçalves a, Madalena Martins a, Ana Loureiro b, Andreia Gomes b, Artur Cavaco-Paulo a,⇑, Carla Silva a,⇑

a IBB-Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal b CBMA (Centre of Molecular and Environmental Biology), Department of Biology, University of Minho, Campus of Gualtar, 4710-057 Braga, Portugal

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Article history:

Received 15 May 2013

Received in revised form 18 July 2013 Accepted 10 August 2013

Available online xxxx


Homogenization Sonication Cavitation Hydroxyl radicals Bleaching

1. Introduction

Textile processes consume high levels of energy and water, thus innovative techniques are being developed to decrease processing time and energy consumption, while reducing the amount of chemicals involved. The use of enzymes in the Textile Industry has become an accepted strategy to overcome those issues [1]. Although the application of enzymes offers many advantages, a few drawbacks related with expensive processing costs and rela- tively slow reaction rates are implicated. The combination of ultra- sonic energy with enzymatic treatments has become a promising approach to improve enzyme efficiency and to accelerate mass transfer during some textile processing steps, namely, desizing, scouring, bleaching, mercerizing and dyeing of textile fibres, while preserving the integrity of the fabrics [1–8]. The implementation of ultrasonic techniques to new wastewater processes for dye degra- dation has also been described [9].

q This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which per- mits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

⇑ Corresponding author. Tel.: +351 253 604400; fax: +351 253 604429.

E-mail addresses: (A. Cavaco-Paulo), cmpsilva@ceb.umin- (C. Silva).

1350-4177/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved.


The main goal of this work is to develop a novel and environmental-friendly technology for cotton bleaching with reduced processing costs. This work exploits a combined laccase–hydrogen peroxide pro- cess assisted by ultrasound. For this purpose, specific reactors were studied, namely ultrasonic power generator type K8 (850 kHz) and ultrasonic bath equipment Ultrasonic cleaner USC600TH (45 kHz). The optimal operating conditions for bleaching were chosen considering the highest levels of hydroxyl radical production and the lowest energy input. The capacity to produce hydroxyl radicals by hydrody- namic cavitation was also assessed in two homogenizers, EmulsiFlexÒ-C3 and APV-2000. Laccase nano- emulsions were produced by high pressure homogenization using BSA (bovine serum albumin) as emulsifier. The bleaching efficiency of these formulations was tested and the results showed higher whiteness values when compared to free laccase. The combination of laccase–hydrogen peroxide process with ultrasound energy produced higher whiteness levels than those obtained by conventional methods. The amount of hydrogen peroxide was reduced 50% as well as the energy consumption in terms of tem- perature (reduction of 40 °C) and operating time (reduction of 90 min).

Ó 2013 Elsevier Inc. All rights reserved.

Cavitation is the formation, growth and subsequent collapse of micro-bubbles or cavities which occur in extremely small intervals of time. It is accompanied by the release of large magnitudes of en- ergy over a very small location producing extreme temperature and pressure gradients [10,11]. The use of ultrasound under opti- mum conditions can enhance diffusivity of enzymes both within and outside the vessel to influence the rates of reaction. Also ultra- sound decreases transport barriers which helps to increase the enzyme:substrate ratio at target site and contribute to reduce the period of treatment by increasing enzyme availability [12–16].

Chlorine and oxygen containing oxidizing agents are used dur- ing conventional bleaching process of cellulosic fibers. When a higher whiteness is needed, it is necessary to perform multiple oxi- dizing treatments. Rapid bleaching with laccase–hydrogen perox- ide enhances the whiteness of cotton fabrics and significantly reduces the amount of hydrogen peroxide required during subse- quent chemical bleaching processes [17]. The enhanced bleaching efficiency associated with a combination of ultrasound technology, laccase and hydrogen peroxide provides or causes less fiber dam- age and greater uniformity of the treatment [2].

The main goal of this research is to develop a novel and environ- mentally beneficial technology to reduce the total processing costs of cotton bleaching consisting in the laccase bleaching of cotton as- sisted by acoustic cavitation (ultrasound). The specific objectives

Please cite this article in press as: I. Gonçalves et al., Sonochemical and hydrodynamic cavitation reactors for laccase/hydrogen peroxide cotton bleaching, Ultrason. Sonochem. (2013),

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