The degradation of caffeine in different kind of effluents, via photo-Fenton process, was investigated in lab-scale and in a solar pilot plant. The treatment conditions (caffeine, Fe(2+) and H(2)O(2) concentrations) were defined by experimental design. The optimized conditions for each variable, obtained using the response factor (% mineralization), were: 52.0 mg L(-1)caffeine, 10.0 mg L(-1)Fe(2+) and 42.0 mg L(-1)H(2)O(2) (replaced in kinetic experiments). Under these conditions, in ultrapure water (UW), the caffeine concentration reached the quantitation limit (0.76 mg L(-1)) after 20 min, and 78% of mineralization was obtained respectively after 120 min of reaction. Using the same conditions, the matrix influence (surface water - SW and sewage treatment plant effluent - STP) on caffeine degradation was also evaluated. The total removal of caffeine in SW was reached at the same time in UW (after 20 min), while 40 min were necessary in STP. Although lower mineralization rates were verified for high organic load, under the same operational conditions, less H(2)O(2) was necessary to mineralize the dissolved organic carbon as the initial organic load increases. A high efficiency of the photo-Fenton process was also observed in caffeine degradation by solar photocatalysis using a CPC reactor, as well as intermediates of low toxicity, demonstrating that photo-Fenton process can be a viable alternative for caffeine removal in wastewater.
Este trabalho descreve a influência e otimização dos reagentes de Fenton (concentração de Fe 2+ e H 2 O 2 ) na eficiência da mineralização do herbicida paraquat (PQT, 50 mg L -1 ) em água, após 60 min (equivalendo a 642 kJ L -1 de radiação UVA acumulada) de tratamento por processo foto-Fenton em escala de laboratório, usando planejamento composto central (CCD). Sob condições otimizadas, experimentos cinéticos foram feitos, avaliando a remoção do PQT, sua mineralização e toxicidade em escala de laboratório, usando irradiação artificial, e em planta piloto sob irradiação solar. A mesma eficiência de remoção e mineralização do PQT foram obtidas em ambos os reatores utilizados. A toxicidade das amostras, estimada em termos de mortalidade de Artemia salina, diminui simultaneamente com o decaimento da concentração de PQT, sugerindo a formação de intermediários de menor toxicidade. Dessa maneira, o processo foto-Fenton/solar pode ser considerado uma alternativa viável para o tratamento de águas residuais contendo PQT.This study describes the influence and optimization of Fenton's reagent (concentration of Fe ) in water, after 60 min (equivalent to 642 kJ L -1 of accumulated UVA radiation) treatment by photo-Fenton process in laboratory scale, using central composite design (CCD). Under optimized conditions, kinetic experiments were done, evaluating the PQT removal, its mineralization and toxicity in laboratory scale, using artificial irradiation, and in a pilot plant under solar irradiation. The same removal efficiency and mineralization of PQT were obtained in both reactors. The toxicity of the samples, estimated in terms of mortality of Artemia salina, decreases simultaneously with the decay of concentration of PQT, suggesting the formation of intermediates of lower toxicity. In this way, the solar photo-Fenton process can be considered as a viable alternative for the treatment of wastewater containing PQT.Keywords: pesticides, detoxification, pilot plant, wastewater treatment, solar light intensity IntroductionSince 2008 Brazil has overtaken the United States in pesticides consumption, becoming the largest consumer. 1 The herbicide paraquat dichloride (PQT, Figure 1) has been widely used for application in post-emergence of weeds and also as desiccant.2 Its residence time in soils can vary from 1.4 to 7.2 years depending on the concentration, soil characteristics (organic matter), temperature and rainfall.3 In river water samples, it has been observed that PQT is not easily microbiologically degraded, since, even after 56 days of incubation, more than 80% of the initial concentration remains unchanged, suggesting to PQT considerable recalcitrance. 4 In addition, PQT is polar, showing high solubility in water, as well as a low octanol-water partition coefficient (log K ow = -4.5), which provides a great mobility in some soils, arriving easily until the next water supplies.5 It has been found in the range of 2-12 mg L -1 in groundwater, 6 and, for example, at average concentration of 0.78 mg L -1 in surface waters ...
We evaluated the use of Fenton reactions induced by solar radiation in the treatment of effluent from a factory of paints for buildings, after prior removal of the suspended solids. The increase of H2O2concentration from 100 to 2500 mg L−1for a [Fe2+] = 105 mg L−1contributed to the reduction of DOC, COD, and toxicity. Our best results were achieved using 1600 mg L−1H2O2, with 90% of DOC and COD removal and a complete removal of the toxicity with respect toArtemia salina. Additionally, through increasing Fe2+concentration from 15 to 45 mg L−1, the DOC removal rate increased 11 times, remaining almost constant in the range above 45 until 105 mg L−1. Under our best experimental conditions, 80% of DOC removal was achieved after an accumulated dose of 130 kJ m−2of UVA radiation (82±17 min of solar irradiation under an average UVA irradiance of34.1±7.3 W m−2), while 40% of DOC removal was reached after 150 min under only thermal Fenton reactions. The results suggest the effectiveness of implementation of solar photo-Fenton process in the decontamination and detoxification of effluents from factories of paints for buildings.
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