Degradação do 2,4,6-triclorofenol através de redução mediada por cobre de valência zero acoplada a oxidação UV/H2O2
During the disinfection stage of water treatment, the combination of the remaining organic matter with free chlorine can lead to the generation of organochlorine compounds. Among these is 2,4,6-trichlorophenol (TCP), with high environmental persistence and carcinogenic character, which is include...
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| Formato: | Dissertação |
| Idioma: | pt_BR |
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| Acesso em linha: | https://repositorio.ufrn.br/jspui/handle/123456789/26681 |
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| Resumo: | During the disinfection stage of water treatment, the combination of the
remaining organic matter with free chlorine can lead to the generation of organochlorine
compounds. Among these is 2,4,6-trichlorophenol (TCP), with high environmental
persistence and carcinogenic character, which is included in the priority list of the United
States Environmental Protection Agency – USEPA. Despite drinking water usually containing
low concentrations of this compound (ng L-1
), its bioaccumulative effect may cause long-term
health problems, which alerts to the need of TCP-contaminated water remediation. Advanced
Oxidative Processes (AOPs) have been successfully applied in the removal of many persistent
pollutants, although in the case of organochlorines, due to their deficient electron groups
(halogens) and consequent oxidation resistance, AOPs effectiveness may drop. However, this
can be surpassed by combining a pre-reductive step before oxidation, thus facilitating
organochlorines degradation. Therefore, the present work proposes a system that couples a
reductive process mediated by zero-valent-copper with an oxidation process mediated by
hydroxyl radicals (
OH). A preliminary study was undertaken to evaluate the influence of
different reaction variables and system conformation: batch and packed bed - column with
recycling. In the latter, different reactive materials were tested, among them copper wires
obtained from electronic waste, as well as different metal and contaminant concentrations,
through statistical experimental design. From this study, the best reductive degradation
conditions were obtained. Then, the degradation of TCP was performed by an advanced
oxidation process (UV / H2O2), in order to compare with the first step. In this one, the
influence of the oxidant concentration (H2O2) was evaluated, in order to adopt the most
suitable for subsequent coupling with the reductive step. Finally, the combination of both
processes was performed, by submitting the solutions that were previously reduced to the
UV/H2O2 process. In both steps two aqueous matrices were tested (deionized and tap water).
Toxicity assays with Vibrio fischeri luminescent bacteria were also carried out, in order to
evaluate the processes effectiveness in the toxicity removal. With the aim of proposing
degradation pathways for each process studied, the reaction intermediates were identified by
mass spectrometry. The results showed that the best reductive reactor configuration was the
packed bed - column, achieving 80% of TCP degradation, with30.6 g of obsolete copper wires
and [TCP] 0 = 10 mg L-1
(0.0506 mmolL-1
). However, this process only led to TCP
dechlorination, not promoting any pollutant mineralization. On the other hand, a total TCP
degradation and 40% mineralization was observed in 4 minutes of oxidation with the UV /
H2O2process, using 0.056 mmol L-1
of H2O2. By coupling the two processes, a 52%
mineralization was achieved within the same reaction period, thus proving that the prereductive step improved the organochlorine oxidation. Solutions presenting high degradation
values from the reductive step were generally more toxic than the parent-compound, while
oxidized solutions presented a certain relation between mineralization and toxicity removal,
although not linearly for all the cases. |
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