This study aimed at investigating the degradation of fungicide carbendazim (CBZ) via photo-Fenton reactions in artificially and solar irradiated photoreactors at laboratory scale and in a semi-pilot scale Raceway Pond Reactor (RPR), respectively. Acute toxicity was monitored by assessing the sensibility of bioluminescent bacteria (Aliivibrio fischeri) to samples taken during reactions. In addition, by-products formed during solar photo-Fenton were identified by liquid chromatography coupled to mass spectrometry (UFLC-MS). For tests performed in lab-scale, two artificial irradiation sources were compared (UV and UV-Vis). A complete design of experiments was performed in the semi-pilot scale RPR in order to optimize reaction conditions (Fe and HO concentrations, and water depth). Efficient degradation of carbendazim (> 96%) and toxicity removal were achieved via artificially irradiated photo-Fenton under both irradiation sources. Control experiments (UV photolysis and UV-Vis peroxidation) were also efficient but led to increased acute toxicity. In addition, HO/UV required longer reaction time (60 minutes) when compared to the photo-Fenton process (less than 1 min). While Fenton's reagent achieved high CBZ and acute toxicity removal, its efficiency demands higher concentration of reagents in comparison to irradiated processes. Solar photo-Fenton removed carbendazim within 15 min of reaction (96%, 0.75 kJ L), and monocarbomethoxyguanidine, benzimidazole isocyanate, and 2-aminobenzimidazole were identified as transformation products. Results suggest that both solar photo-Fenton and artificially irradiated systems are promising routes for carbendazim degradation.
A atrazina é um dos agrotóxicos mais utilizados no Brasil e possui grande tendência a contaminar águas superficiais e subterrâneas. Logo, o objetivo do estudo foi realizar uma revisão bibliográfica para verificar a ocorrência da atrazina em águas superficiais, subterrâneas e tratadas no Brasil e sua remoção durante o tratamento de água para consumo humano. Para tanto, buscaram-se na literatura trabalhos científicos publicados entre os anos de 2000 e 2017 que trataram sobre a presença do composto nas matrizes supracitadas. Para a análise da remoção da atrazina em água buscaram-se trabalhos que empregaram processos como tratamento convencional, ozonização, fotólise, adsorção, nanofiltração, entre outros. Utilizaram-se como plataformas de pesquisa o Periódicos Capes, Google Acadêmico e Science Direct. Analisaram-se 36 trabalhos referentes a presença do composto em águas no Brasil e 43 sobre sua remoção da água. Observou-se nos trabalhos revisados, frequências de detecção da atrazina da ordem de 8% para águas superficiais e 12% para subterrâneas, além de sua ocorrência em valores superiores ao VMP em ambas as matrizes. Em águas tratadas a presença, bem como concentração da atrazina foi reportada em dois estudos, porém em concentrações inferiores à máxima permitida. O tratamento de ciclo completo é ineficaz para a remoção da atrazina. Sendo assim, é necessária a associação de outros processos ao tratamento convencional, dentre os quais citam-se: a adsorção em carvão ativado, ozonização, nanofiltração, osmose inversa e processos oxidativos avançados. Porém, é importante se atentar á conversão dos contaminantes a subprodutos que, assim como seus precursores, podem apresentar toxicidade.
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The goal of this work was to evaluate the performance of the LED irradiated photo-Fenton process on the removal of (i) estrogenic activity and (ii) seven endocrine disruptors (EDs) (4-octylphenol, 4-nonylphenol, bisphenol A, estrone, 17β-estradiol, 17α-ethinylestradiol, and estriol) from real wastewater treatment plant effluent (WWTPE). EDs are a group of contaminants of emerging concern present in WWTPE and which may be recognized by hormone receptors, thus harming animal and human health. The yeast estrogenic screen test (YES) was used to quantify estrogenic activity promoted by EDs in WWTPE samples before and after photo-Fenton treatment. Tests were performed following a factorial design with different iron (20, 40, and 60 mg L −1) and hydrogen peroxide (100, 200, and 300 mg L −1) concentrations in a laboratory scale LED photoreactor (λ = 455 nm, 1.5 L, 1.6 × 10 −6 Einstein s −1). EDs were analyzed by gas chromatography coupled to a mass spectrometer. Control experiments consisted of Fenton process, iron only, LED irradiation only, and H 2 O 2 only. Optimum experimental conditions for LED photo-Fenton resulted in 62% removal of estrogenic activity and 59% mineralization. In addition, treated WWTPE was not toxic to Aliivibrio fischeri and more than 80% of EDs were removed during LED irradiated photo-Fenton. Although Fenton process showed similar efficiency to that obtained by LED photo-Fenton, a higher volume of sludge was generated in the dark. Finally, results obtained in this study confirm the applicability of LED irradiated photo-Fenton process for improving the quality of WWTPE as an alternative to solar photo-Fenton in case solar radiation is not available, thus reducing hazards associated to WWTPE reuse or discharge.
The objective of this work was to study the degradation and mineralization of ethylenethiourea (ETU) in water by ozonation at different pH values and in the presence of hydrogen peroxide. Degradation experiments were performed using an initial ETU concentration of 50 ppm for 180 min with a gas flux of 0.25 dm(3) min(-1) and an O3 production rate of 12.1 mg min(-1). Degradation of by-products was monitored by direct injection electrospray ionization mass spectrometry (ESI-MS), ETU concentration was determined by HPLC-UV, and its mineralization was detected by total organic carbon (TOC) analysis. Optimum degradation of ETU in water was observed at pH = 11, whereas at pH = 3, the degradation of ETU was slowest, indicating that the reaction occurred through different mechanisms. The additional effects of hydroxyl radicals formed at the highest pH can be used to explain the results obtained in this study. Peroxone experiments were carried out in the presence of 400 and 800 mg L(-1) H2O2; the degradation of ETU was faster at 400 mg L(-1) H2O2. This was attributed to the scavenging effect of the excess H2O2. ETU treatment by ozonation produced several by-products of degradation such as ethylene urea and 2-imidazoline.
This study evaluated the adsorption capacity of ethylenthiourea (ETU) and 1H-1,2,4-triazole (1,2,4-T) for two commercial activated carbons: charcoal-powdered activated carbon (CPAC) and bovine bone-powdered activated carbon (BPAC). The tests were conducted at a bench scale, with ETU and 1,2,4-T diluted in water, for isotherm and adsorption kinetic studies. The removal of the compounds was accompanied by a total organic carbon (TOC) analysis and ultraviolet (UV) reduction analysis. The coals were characterized by their surface area using nitrogen adsorption/desorption, by a scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) and by a zero charge point analysis (pHpcz). The results showed that adsorption kinetics followed a pseudo-second-order model for both coals, and the adsorption isotherms for CPAC and BPAC were adjusted to the Langmuir and Freundlich isotherms, respectively. The CPAC removed approximately 77% of the ETU and 76% of the 1,2,4-T. The BPAC was ineffective at removing the contaminants.
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