Comparison of flutamide degradation via UV/TiO 2 , UV/H 2 O 2 and UV/H 2 O 2 /TiO 2 systems

Synthetic solutions of flutamide were subject to degradation using three advanced oxidation systems, namely UV/TiO 2 , UV/H 2 O 2 and UV/H 2 O 2 /TiO 2 . Optimum conditions and degradation kinetics has been established for all three systems. The experimental results showed that all three systems can be successfully used for flutamide degradation with efficiencies higher than 99% and that advanced oxidation processes are showing good potential for degradation of organic pollutants that cannot be suitable removed/degraded using conventional wastewater treatment processes.


INTRODUCTION
Flutamide (FT) is a nonsteroidal androgen drug used in cancer treatment but also in transgender hormone therapy and hair and skin conditions. Even if based on available studies at European level [1][2] both the frequency (1%) and concentrations (µg/L) of FT within wastewater treatment plants effluents are rather low, it proved to be resistant to both chemical oxidation using ClO2 [3] and ozone treatment [4]. A possible explanation to this behaviour is FT structure, which contains electron withdrawing fluoro groups. FT has been indicated also as an endocrine disruptor [5]. There is limited information available within the literature related to the use of advanced oxidation processes for FT degradation, available studies are mainly focussing on FT photochemistry in various media [6]. In the last years there are available some studies focussing on FT degradation via solar photo-Fenton [7][8] and heterogeneous photo Fenton coupled with ozone treatment [9]. Preliminary data on FT degradation via TiO2 assisted photo catalyse are also available [10].

EXPERIMENTAL PART
FT degradation experiments were performed with a UV reactor (Heraeus type) equipped with a TQ 150-Z3 medium pressure mercury lamp. Used reagents were FT (Sigma), TiO2 (Merck), 30% H2O2 solution (Fluka). FT synthetic solutions were prepared using FT (purity ≥ 99%) produced by Sigma -Aldrich and ultrapure water generated by a Milli-Q Integral 15 system (Merck Millipore). FT concentration was monitored by HPLC technique and F -, NH4 + , NO3 -, NO2concentration were determined via ion chromatography.

UV/TiO2 system
Previously reported work confirmed that FT degradation using UV/TiO2 system take place with efficiencies above 95%, in optimum operating conditions [10]. Experiments were resumed in order to refine optimum parameters for FT degradation. Synthetic solution with an initial concentration Prolonging of irradiation time proved to have a positive effect upon FT degradation efficiency, which reached more than 99% after 180 minutes of irradiation. The linearization of FT degradation by a pseudo-first order kinetic led to the calculation of degradation rate constant, which was found to be equal with 2.72 x 10 -2 min -1 , based on the following equations: (2) where [FT] is flutamide concentration at a given time t, [FT]0 is flutamide initial concentration, k is FT degradation rate constant and t is irradiation time. Formation of intermediary transformation products with F and N is proved by the mineralisation efficiencies that are permanently lower than FT degradation efficiency. Langmuir-Hinshelwood kinetic is commonly used to describe heterogeneous catalytic processes and therefore was also used for FT degradation via UV/TiO2 system in accordance with the following equations [11]: where r0 is initial FT degradation rate, [FT]0 is flutamide initial concentration, kr is FT degradation rate constant, Kads is equilibrium constant for FT adsorbtion-desorbtion on catalyst surface particles. Equation 3 can be rearranged in the following expression:   FT degradation via UV/H2O2 system occurs with much better degradation efficiencies compared with UV/TiO2 system. For the same initial FT concentration, the efficiencies of FT degradation using UV/H2O2 system are above 97% (for all applied H2O2 doses) after 30 minutes of irradiation in comparison with FT degradation efficiency of only 54.57% via UV/TiO2 system after the same period of irradiation. F mineralization efficiency are also higher for UV/H2O2 system compared with UV/TiO2 system. FT degradation efficiency in UV/H2O2 system are increasing with the increase of H2O2 concentration but the marginal value of the increase become lower. This behaviour can be explained by combination of two opposite processes [12]. Photolysis with generation of hydroxyl radicals that are reacting with FT: Absorbtion/screening of UV radiation and scaveging of hydroxil radicals: UV/H2O2/TiO2 system The UV/H2O2 system is representing the rapid alternative but is inducing higher costs compared with UV/TiO2 system, which presents the disadvantage of longer irradiation time. A combination of both processes was envisaged in order to set up the most convenient alternative from the point of view of both irradiation time and reagents costs.
In order to ease the comparison process the same initial FT concentration [FT]0 = 8.08 mg/L was used.

Electric energy per order
In order to assess energy consumptions for all three tested variants, electric energy per order EEO was used [13], according to equation (11): (11) where EEO is electric energy per order expressed in kWh m -3 order -1 , P is the power of UV lamp in kW (0.15 kW), t is the irradiation time in minutes, V is the volume of treated sample in L (0.4 L), [FT]0/[FT] is the ratio between FT initial concentration and FT concentration at the given t time.
Based on EEO calculated value, presented in the Table 4, it was found that the optimum system for FT degradation from the point of view of energy consumption is represented by the UV/H2O2/TiO2 system.

CONCLUSIONS
Based on obtained experimental results the UV/H2O2/TiO2 system seems to be the suitable option for FT degradation. It combines the main advantages of UV/TiO2 (low cost, catalyst reuse) and UV/H2O2 (short degradation time, low electric energy per order) systems and minimize their disadvantages, which are mainly link to H2O2 cost and the need for an additional step for catalyst separation and reuse.