Hindawi Publishing Corporation International Journal of Chemical Engineering Volume 2013, Article ID 393467, 5 pages http://dx.doi.org/10.1155/2013/393467 Research Article The Application of a Surface Response Methodology in the Solar/UV-Induced Degradation of Dairy Wastewater Using Immobilized ZnO as a Semiconductor Gisella R. Lamas Samanamud, 1,2 Helcio J. Izario Filho, 1 Carla C. A. Loures, 1,3 Ivy S. Oliveira, 1 Andre L. Souza, 1 Ana Paula B. R. de Freitas, 1,3 and Ruoting Pei 2 1 Department of Chemical Engineering, Engineering School of Lorena, University of Sao Paulo (USP), Estrada Municipal do Campinho, s/n ∘ , Bairro do Campinho, 126020-810 Lorena, SP, Brazil 2 Department of Civil and Environmental Engineering, University of Texas at San Antonio (UTSA), One UTSA Circle, San Antonio, TX 78249, USA 3 Departament of Production Engineering, Sao Paulo State University (UNESP), 12516-410 Guaratingueta, SP, Brazil Correspondence should be addressed to Gisella R. Lamas Samanamud; zeldals@hotmail.com Received 30 May 2013; Accepted 15 August 2013 Academic Editor: Antonia P´ erez de los R´ ıos Copyright © 2013 Gisella R. Lamas Samanamud et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. An Advanced Oxidation Process (AOPs) was carried out in this study with the use of immobilized ZnO and solar/UV as an energy source to degrade dairy wastewater. he semibatch reactor system consisted of metal plate of 800 × 250 mm and a glass tank. he reaction time was of 3 h for 3 L of dairy wastewater. Experiments were performed based on a surface response methodology in order to optimize the photocatalytic process. Degradation was measured in percentage terms by total organic carbon (TOC). he entry variables were ZnO coating thickness and pH, using three levels of each variable. he optimized results showed a TOC degradation of 31.7%. Optimal parameters were metal-plate coating of 100 m of ZnO and pH of 8.0. Since solar/UV is a constant and free energy source in most tropical countries, this process tends to suggest an interesting contribution in dairy wastewater treatment, especially as a pretreatment and the optimal conditions to guarantee a better eiciency of the process. 1. Introduction he use of ZnO as a semiconductor was studied for possible application in a photo-excitation-initiated degradation of the catalyst followed by the formation of a surface bandgap (see (1)). he oxidation potential (h VB + ) permits the formation of active intermediates by the direct oxidation of an organic matter (see (2)). Many reactive hydroxyl radicals can be formed either by decomposition of water or by a bandgap reaction with OH − (see (3) and (4)). he Hydroxyl radical is a powerful nonselective oxidation agent leading to organic pollutants degradation [1–3]. Consider that ZnO +ℎ] → ZnO (e CB − + h VB + ) (1) h VB + + organic matter − → oxidation products (intermediates) (2) h VB + + H 2 O → H + + ∙ OH (3) h VB + + OH − → ∙ OH (4) he methodologies used in the design of experiments allow a similar result as the one obtained from conventional experiments with the advantage of the use of fewer exper- iments. hus, a good design of experiments can provide suicient results for an efective statistical analysis [4]. In order to obtain the optimized variables for the study of