Potencial do processo foto-Fenton como etapa complementar ao tratamento de esgoto urbano e efluentes de indústria agroquímica

Abstract

This work evaluated the potential of photo-Fenton process as a complementary step to the treatment of urban sewage aiming at the degradation of ciprofloxacin (CIP) (3.3 mg L–1) and fipronil (FIP) (1.0 mg L–1). In addition, this process was evaluated as an alternative treatment for decontamination and toxicity reduction of an agrochemical effluent containing 403 mg L–1 of ametrine (AMT), 2153 mg L–1 of atrazine (ATZ), 2936 mg L–1 of imidacloprid (IMD) and 3354 mg L–1 of tebuthiuron (TBT). Initially, a preliminary study was carried out to evaluate the influence of operational parameters (pH, source and iron concentration and, molar Fe3+/ligand ratio) on the performance of the modified photo-Fenton process for the degradation of CIP and FIP at near to environmental conditions. 90% of CIP degradation were obtained in distilled water at pH 6.0–6.5 using 10 μmol L–1 of FeCit while 98% of FIP degradation (using 32 μmol L–1 of FeCit) were obtained using the molar Fe3+/citrate ratio equivalent to 1:3. 83% of FIP degradation was obtained in sewage treatment plant effluent (STP) at pH 6.0. However, FeCit concentration had to increase 6 times (192 μmol L–1) to reach this efficiency due to the influence of organic matter and inorganic ions present in the STP effluent. Three and eight transformation products (TP) were detected for CIP and FIP, respectively. Results revealed that the degradation of CIP and FIP through the photo-Fenton process occurred preferentially via HO• attack on the piperazine ring of CIP and the pyrazole ring of FIP. The treatment of the agrochemical effluent initially occurred via coagulation-flocculation-settling (using 8 mmol L–1 of Fe(NO3)3) and reached 99% removal of both color and turbidity. Then, the photo-Fenton process was applied resulting in effective degradation of pesticides ([AMT, ATZ, IMD and TBT] ≤ 10 μg L–1 (using 2 mmol L–1 of FeOx and sunlight)). In addition, 79% and 71% reduction of chemical oxygen demand (COD) and biological oxygen demand (BOD5), respectively, were obtained. The use of solar radiation in the photo-Fenton process enhanced degradation kinetics of target compounds when compared to experiments performed under black light lamps. Acute toxicity monitoring (mortality of the D. melanogaster flies (for FIP) and the inhibition of luminescence emitted by V. fischeri (for the agrochemical effluent)) indicated that the photo-Fenton process was effective in the degradation of CIP and FIP as well as for toxicity reduction. In general, these results show that the photo-Fenton process is a viable alternative for the degradation of emerging contaminants in distilled water and STP effluent and, also for the treatment of agrochemical effluent.