Avaliação do efeito de ligantes orgânicos na degradação de naproxeno pelo processo foto-Fenton em condições neutras

Abstract

Naproxen (NAP) is an anti-inflammatory frequently detected in surface and potable water at concentrations of ng to μg L−1, due to the inefficiency of conventional processes used in sewage treatment plants (STP). Thus, it can cause negative effects on the health of living beings. For this reason, advanced oxidation processes (AOP) have been studied in order to overcome this issue. In this work, the effect of ferric organic ligands (L): oxalate (Ox), citrate (Cit), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) and N, N'-disuccinic acid ethylenediamine (EDDS) was evaluated in the degradation of NAP by the modified photo-Fenton process. The organic complexes keep the iron species soluble in a wide pH range, allowing application of this process in a medium close to neutrality. The influence of operational parameters (molar ratio between Fe/L, concentration of hydrogen peroxide - H2O2 and potassium persulfate - K2S2O8) was evaluated, aiming to determine the best experimental condition for the maximum degradation of 230 μg L−1 of NAP, in different aqueous media and radiation and, initial pH 7.0. First, the influence of the molar ratio between Fe/L and [H2O2] in distilled water was evaluated. The optimized conditions (1:1 for Fe/EDDS and Fe/NTA, 1:2 for Fe/EDTA and 1:3 for Fe/Cit, in the presence of 0.56 mg L−1 of Fe3+ and 4.1 mg L−1 of H2O2) provided effective degradation of NAP, under artificial and solar radiation, reaching in all cases concentrations below the LQ (< 38 μg L−1) of method. In the presence of 32.4 mg L−1 of K2S2O8 it was observed that doses of accumulated energy were reached close to those obtained when H2O2 was used. The degradation efficiency of the drug was markedly better, for all complexes and oxidants, when sunlight was used. Subsequently, the optimized POA in distilled water was applied in STP effluent with improvement of [Fe3+, H2O2 and K2S2O8]. The optimized conditions 1.2 mg L−1 of Fe3+ (concentration present in the effluent), 167 mg L−1 of H2O2 and 663 mg L−1 of K2S2O8, demonstrated that 63.2 kJ m−2 of energy dose was required for the drug degradation reaches LQ (< 19 μg L−1) using Fe/Cit, Fe/NTA and Fe/EDTA and 95.1 kJ m−2 for Fe/EDDS, using the Fe/L/H2O2 system. Better results of NAP degradation in STP effluent were obtained using the Fe/L/K2S2O8 system, as it took only 23.5 kJ m−2 of energy dose to degrade the NAP using Fe/NTA and Fe/EDTA and 31.4 kJ m−2 for Fe/Cit and Fe/EDDS. The complexity of the STP effluent directly influenced the comparison between the L, because in a real matrix, better degradation results were observed when Fe/NTA was used. In addition, the comparison between the L allowed us to define that the use of Fe/Cit (1:3) had the lowest cost benefit compared to the other evaluated complexes. The addition of Cit contributed to the of the organic load of the real effluent with 4.54 mg L−1 of carbon, however, it is considered non-toxic and biodegradable. Therefore, the evaluation of the effect of L on the degradation of NAP in effluent STP by the studied AOP and the conditions established in this work demonstrated to be effective in the degradation of NAP in neutral medium and can be considered as a viable option for the tertiary treatment of wastewater from STP.