Decolouration of textile dyes in wastewaters by photocatalysis with TiO 2 O. Prieto a , J. Fermoso a, * , Y. Nun ˜ez a , J.L. del Valle b , R. Irusta a,c a Automation, Robotics, Information and Manufacturing Technology Centre (CARTIF), Boecillo Technology Park, 205-47151 Boecillo, Valladolid, Spain b FASA RENAULT, Madrid Road Km. 185.3, 47008 Valladolid, Spain c Department of Chemical Engineering and Environmental Technology, School of Industrial Engineering, University of Valladolid, Spain Received 21 July 2004; received in revised form 27 October 2004; accepted 23 February 2005 Available online 24 May 2005 Communicated by: Associate Editor Sixto Malato-Rodrı ´guez Abstract The photocatalytic removal of colour of a synthetic textile effluent, using TiO 2 suspensions under solar radiation, has been studied at pilot plant scale. A synthetic dye solution was prepared by a mix of six commercial textile dyes. A pho- tochemical reactor of parallel CPC reflectors with UV-transparent tubular receivers was used. The study of photodeg- radation was carried out using the TaguchiÕs parameter design method. Following this methodology, the reaction was conducted under different flow conditions, pH and H 2 O 2 concentrations. The results show that all dyes used in the expe- riences can be degraded successfully by photo-oxidation. The process shows a significant enhancement when it is carried out at high flows, alkaline media and high H 2 O 2 concentration. Colour removal from the effluent was reached at 55 min operating time. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Textile dyes; Photocatalysis; Solar radiation 1. Introduction Textile dyes and other industrial dyestuffs constitute one of the largest group of organic compounds that represent an increasing environmental danger. About 1–20% of the total world production of dyes is lost during the dyeing process and is released in the textile effluents (Houas et al., 2001). The release of those col- oured waste waters in the environment is a considerable source of non-aesthetic pollution and eutrophication and can originate dangerous byproducts through oxidation, hydrolysis, or other chemical reactions taking place in the wastewater phase (Bianco-Prevot et al., 2001). Colour in textile effluents has become particularly identified with the dyeing of cotton products and the use of reactive azo dyes since up to 30% of the used dye- stuffs remain in the spent dye-bath after the dyeing pro- cess (Easton, 1995). The commonly used method for the treatment of textile wastewater is the combination of 0038-092X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.solener.2005.02.023 * Corresponding author. Tel.: +34 983 546 504; fax: +34 983 546 521. E-mail addresses: josdom@cartif.es (J. Fermoso), rubiru@ eis.uva.es (R. Irusta). Solar Energy 79 (2005) 376–383 www.elsevier.com/locate/solener