materials Article Using Central Composite Experimental Design to Optimize the Degradation of Tylosin from Aqueous Solution by Photo-Fenton Reaction Abd Elaziz Sarrai 1,2,3,*, Salah Hanini 1, Nachida Kasbadji Merzouk 2, Djilali Tassalit 2, Tibor Szabó 3, Klára Hernádi 4 and László Nagy 3 1 Laboratory for Biomaterials and Transport Phenomena LBMPT, University Yahia Fares, Medea 26000, Algeria; [email protected] 2 Unité de Développement des Equipements Solaires, UDES/Centre de Développement des Energies Renouvelables, CDER, Bou Ismail, Tipaza 42415, Algeria; [email protected] (N.K.M.); [email protected] (D.T.) 3 Department of Medical Physics and Informatics, University of Szeged, Szeged 6720, Hungary; [email protected] (T.S.); [email protected] (L.N.) 4 Department of Applied and Environmental Chemistry, University of Szeged, Szeged 6720, Hungary; [email protected] * Correspondence: [email protected]; Tel.: +213-778-89-58-91 Academic Editor: Naozumi Teramoto Received: 18 March 2016; Accepted: 24 May 2016; Published: 30 May 2016 Abstract: The feasibility of the application of the Photo-Fenton process in the treatment of aqueous solution contaminated by Tylosin antibiotic was evaluated. The Response Surface Methodology (RSM) based on Central Composite Design (CCD) was used to evaluate and optimize the effect of hydrogen peroxide, ferrous ion concentration and initial pH as independent variables on the total organic carbon (TOC) removal as the response function. The interaction effects and optimal parameters were obtained by using MODDE software. The significance of the independent variables and their interactions was tested by means of analysis of variance (ANOVA) with a 95% confidence level. Results show that the concentration of the ferrous ion and pH were the main parameters affecting TOC removal, while peroxide concentration had a slight effect on the reaction. The optimum operating conditions to achieve maximum TOC removal were determined. The model prediction for maximum TOC removal was compared to the experimental result at optimal operating conditions. A good agreement between the model prediction and experimental results confirms the soundness of the developed model. Keywords: Photo-Fenton; Tylosin; RSM; CCD 1. Introduction During the last two decades, an increasing interest has been shown in the ecological effects of pharmaceuticals and personal care products, which are released into the environment every year [1,2]. Antibiotics are a special group of pharmaceutical compounds used to control infectious diseases in human and veterinary medicine. A residual concentration has been detected in various environmental compartments worldwide due to the fact that a large portion of the consumed antibiotics are not completely metabolized (and thus are excreted as active substances) and the conventional wastewater treatment methods fail to completely remove them from the solution [3–5]. Their presence in aquatic systems increases the resistance of bacteria to the antibiotic functions of these chemicals, raising great concern about their transport, fate, ecological effects and risk in the environment [6–8]. The existence of antibiotics in natural water bodies poses serious threats to human health. Besides human health, Materials 2016, 9, 428; doi:10.3390/ma9060428 www.mdpi.com/journal/materials Materials 2016, 9, 428 2 of 11 Materials 2016, 9, 428 2 of 11 human health. Besides human health, toxic effects of antibiotics on aquatic and edaphic organisms alsotoxic pose effects an ecological of antibiotics risk on[9–11]. aquatic The and environm edaphicental organisms exposure also of antibiotics pose an ecological could increase risk [9 –the11 ]. possibilityThe environmental of changes exposure in the microbial of antibiotics populations could increase to degrade the possibilitycontaminants of changessuch as pesticides in the microbial [12], andpopulations have a todeleterious degrade contaminants effect on important such as pesticides biogeochemical [12], and havecycles a deleterious such as effectnitrification on important and denitrificationbiogeochemical [13]. cycles such as nitrification and denitrification [13]. AmongAmong veterinary veterinary pharmaceuticals, pharmaceuticals, Tylosin Tylosin (Figure (Figure 1)1) is is a a macrolide macrolide antibiotic antibiotic produced produced by by the the fermentationfermentation of of Streptomyces Streptomyces stra strains.ins. It Itconsists consists of of a asubstitute substitutedd 16-membered 16-membered lactone, lactone, an an amino amino sugarsugar (mycaminose) (mycaminose) and and two two neutral neutral sugars, sugars, mycinose mycinose and and mycarose. mycarose. Tylosin Tylosin is is used used extensively extensively as as aa therapeutic therapeutic substance substance in in the the treatment treatment of of mycoplasmosis mycoplasmosis in in poultry poultry and and livestock livestock [14]. [14]. O O O HO O OH O O O O N O OH O O O HO HO Figure 1. Chemical structure of Tylosin. Figure 1. Chemical structure of Tylosin. FentonFenton and and photo-Fenton photo-Fenton are are practical practical advanc advanceded oxidation oxidation processes, processes, used used for for treating treating wastewaterwastewater containing containing pharmaceutical pharmaceutical products, products, in in particular particular antibiotics antibiotics [15]. [15]. The The Fenton Fenton process process 2+ (Fe(Fe2+/H/H2O22O/dark)2/dark) (Equations (Equations (1)–(6)) (1)–(6)) is a is homogeneous a homogeneous catalytic catalytic oxidation oxidation process process that that uses uses a amixture mixture 2+ 2+ ofof H H2O2O2 2andand Fe Fe2+ inin an an acidic acidic environment; environment; the the reaction reaction between between dissolved dissolved Fe Fe2+ andand H H2O2O2 2leadsleads to to the the oxidationoxidation of of Fe Fe2+2+ toto Fe Fe3+ 3+andand the the production production of ofhydroxyl hydroxyl radicals radicals (HO (HO.) [16]..)[16 ]. Fe2+ + H2O2 Fe3+ +OH. + OH− (1) 2+ 3+ . ´ Fe Fe+ H2+ 2+O OH2 . ÝÑ FeFe3+ + +OH OH− + OH (2) (1) Fe2+ OH+ OH. + .Organics ÝÑ ProductsFe3+ + OH ´ (3) (2) . OH OH+ Organics. + H2O2 ÝÑ HProducts2O + H2O. (4) (3) . OH OH+ H.2+O OH2 . ÝÑ HH2O2O2 + H2O (5) (4) . OH Fe+ OH3+ + H2O2 ÝÑ FeOOHH2O2 2+ + H+ (6) (5) Fe3+ + H O ÝÑ FeOOH2+ + H+ (6) These reactions show2 2that hydrogen peroxide may be consumed when it reacts with Fe2+, as shown in Equation (1), producing hydroxyl radicals that will degrade organic compounds through These reactions show that hydrogen peroxide may be consumed when it reacts with Fe2+, Equation (3). Hydrogen peroxide can also react with Fe3+ via Equation (6), but the major drawback of as shown in Equation (1), producing hydroxyl radicals that will degrade organic compounds the Fenton reaction is the production of Fe(OH)3 sludge that requires further separation and disposal through Equation (3). Hydrogen peroxide can also react with Fe3+ via Equation (6), but the major [17]. The rate of reaction in the Fenton process can be further enhanced by the application of drawback of the Fenton reaction is the production of Fe(OH) sludge that requires further separation ultraviolet irradiation sources, also known as the photo-assisted3 Fenton system [18,19]. The and disposal [17]. The rate of reaction in the Fenton process can be further enhanced by the photo-Fenton or photo-assisted Fenton (Fe2+/H2O2/light) process involves irradiation with sunlight application of ultraviolet irradiation sources, also known as the photo-assisted Fenton system [18,19]. or an artificial light, and it has shown efficiency in minimizing sludge formation and improving the The photo-Fenton or photo-assisted Fenton (Fe2+/H O /light) process involves irradiation with degradation efficiency [17]. Applying UV irradiation2 to2 the Fenton reaction can enhance the sunlight or an artificial light, and it has shown efficiency in minimizing sludge formation and improving oxidation rate of organic compounds by the photo-reduction of produced ferric ions (Fe3+) and ferric the degradation efficiency [17]. Applying UV irradiation to the Fenton reaction can enhance the complexes. Ferrous ions are recycled continuously by irradiation so they are not depleted during the Materials 2016, 9, 428 3 of 11 oxidation rate of organic compounds by the photo-reduction of produced ferric ions (Fe3+) and ferric Materials 2016, 9, 428 3 of 11 complexes. Ferrous ions are recycled continuously by irradiation so they are not depleted during the course of the oxidation reaction, as shown in Equation (7). The photo-reduction of ferric to ferrous course of the oxidation reaction, as shown in Equation (7). The photo-reduction of ferric to ferrous ions is promoted concomitantly with the generation of additional HO., according to Equation (8) [20]. ions is promoted concomitantly with the generation of additional HO., according to Equation (8) [20]. 3+3+ 2+ 2+ + + FeFe + H 2OO ÝÑ Fe(OH)Fe(OH) + H + H (7) (7) Fe(OH)Fe(OH)2+2+ + һʋ ÝÑ Fe2+Fe+OH2+ +. OH. (8) (8) Different parameters such as hydrogen peroxide, ferrous ion concentration and pH could affect Different parameters such as hydrogen peroxide, ferrous ion concentration and pH could affect the degradation in the photo-Fenton process. In most published studies, the effect of each variable the degradation in the photo-Fenton process. In most published studies, the effect of each variable was studied independently, with the other variables kept constant. This approach fails to consider was studied independently, with the other variables