RESUMO
The contamination of water bodies by synthetic organic compounds coupled with climate change and the growing demand for water supply calls for new approaches to water management and treatment. To tackle the decontamination issue, the activation of peroxymonosulfate (PMS) using copper magnetic ferrite (CuMF) nanoparticles prepared under distinct synthesis conditions was assessed to oxidize imidacloprid (IMD) insecticide. After optimization of some operational variables, such as CuMF load (62.5-250 mg L-1), PMS concentration (250-1000 µM), and solution pH (3-10), IMD was completely oxidized in 2 h without interferences from leached metal ions. Such performance was also achieved when using tap water but was inhibited by a simulated municipal wastewater due to scavenging effects promoted by inorganic and organic species. Although there was evidence of the presence of sulfate radicals and singlet oxygen oxidizing species, only four intermediate compounds were detected by liquid chromatography coupled to mass spectrometry analysis, mainly due to hydroxyl addition reactions. Concerning the changes in surface properties of CuMF after use, no morphological or structural changes were observed except a small increase in the charge transfer resistance. Based on the changes of terminal surface groups, PMS activation occurred on Fe sites.
RESUMO
This work focuses on the development of electro-absorption and photoelectro-absorption technologies to treat gases produced by a synthetic waste containing the highly volatile perchloroethylene (PCE). To do this, a packed absorption column coupled with a UV lamp and an undivided electrooxidation cell was used. Firstly, it was confirmed that the absorption in a packed column is a viable method to achieve retention of PCE into an absorbent-electrolyte liquid. It was observed that PCE does not only absorb but it was also transformed into phosgene and other by-products. Later, it was confirmed that the electro-absorption process influenced the PCE degradation, favoring the transformation of phosgene into final products. Opposite to what is expected, carbon dioxide is not the main product obtained, but carbon tetrachloride and trichloroacetic acid. Both species are also hazardous but their higher solubility in water opens possibilities for a successful and more environmental-friendly removal. The coupling with UV-irradiation has a negative impact on the degradation of phosgene. Finally, a reaction mechanism was proposed for the degradation of PCE based on the experimental observations. Results were not as expected during the planning of the experimental work but it is important to take in mind that PCE decomposition occurs in wet conditions, regardless of the applied technology, and this work is a first approach to try to solve the treatment problems associated to PCE gaseous waste flows in a realistic way.
