Acoplamento ferro zero e radical sulfato (ZVI + SO4>sup<&bull;->/sup<) para a remoção de contaminantes emergentes

Abstract

Water is an abundant and poorly distributed resource on the planet, being its management a global concern, present in national and international regulations. Although water and wastewater treatment stations are efficient for their projected purposes, they are not for eliminating species that occur in the environment at the ng L -1 to µg L -1 range. Such species, the so-called Contaminants of Emerging Concern (CECs), usually are not legislated; neither their effects on the local biogeochemistry are clearly understood. To eliminate them, technologies such as the Advanced Oxidative Processes (AOPs) are widely studied. The aim of this study was to maximize the degradation of three CECs: caffeine (CAF), bisphenol A (BPA), and 17αethinyl estradiol (EE2), in concentrations close to the ones found in wastewater treatment plants (100 µg L -1 ), using the zero-valent iron (ZVI) process coupled to the sulfate radical (SO4 •-), generated by persulfate. A multiresidue chromatographic method in HPLC-UV was developed (isocratic, reversed phase), in which separations took 12.5 min with hydromethanolic mobile phase. Samples preparation was accomplished by solid phase extraction (SPE), using Strata-X cartridges from Phenomenex, with recoveries greater than 80% and good linearity (R 2 > 0.98). The ZVI process was studied via a 2 2 factorial design. Degradations ranged from 9.9 to 35.5%, and neither pH (4 and 6) nor flow rates (15 and 35 mL min -1 ) were statistically significant (95% confidence level). Fe 2+ concentrations varied from 2 to 12 mg L -1 , within the established legal limit for effluent discharge in Brazil (15 mg L -1 ). In the ZVI/persulfate coupling, which was studied via another 2 2 factorial design, pH (4 and 6) and the interaction between pH and sodium persulfate concentration (0.50 and 1.0 mmol L -1 ) were statistically significant (95% confidence level), reaching degradations up to 64%. Additionally, a 2 2 factorial design was performed assessing the use of citric acid (0.009 and 0.036 mmol L -1 ) and UV-A light (4 and 6 lamps, 4 W each). Only the number of lamps was statistically significant, with degradations up to 74%. The best degradation conditions were: flow rate = 15 mL min -1 , pH = 6, [Na2S2O8] = 1.0 mmol L -1 , [citric acid] = 0.009 mmo L -1 , and irradiation with 4 UV-A lamps.