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 ...

In this study it was evaluated the role of the composition of sanitary landfill leachate on the removal of dissolved organic carbon (DOC) by photo-Fenton process. The composition of the matrix (high turbidity and color, as well as presence of inorganic ions sulfate and chloride) does not reduce the efficiency of DOC removal by photo-Fenton reactions, but influences significantly the reaction time and consumption of H 2 O 2 . An expressive increase in the efficiency of DOC removal occurred for concentrations of Fe 2+ between 50 and 100 mg L -1, remaining constant in the range between 100 and 200 mg L -1 . On the other hand, the pre-treatment of this effluent by coagulationflocculation before the photo-Fenton process is recommended, since a similar efficiency of DOC removal, between 70 and 77%, was achieved using only 17% of the time and 7% of H 2 O 2 necessary for the treatment of raw leachate treatment.

This study reports a protocol for the treatment of a sanitary landfill leachate through integration between a stage of coagulation-flocculation, a step of filtration of the resulting suspension, and application of the photo-Fenton process using a ferrioxalate complex and solar irradiation. The best results for turbidity removal by coagulation-flocculation were reached using Al 3+ as nitrate salt mainly using concentrations up close 4.4 mmol L -1 , at the natural pH of the effluent (pH 7.9), when the removal of 66% of the turbidity was achieved. By using a ferrioxalate complex after adjusting the pH of the effluent to 5, it was possible to circumvent the classical limitations of the Fenton process (related to the pH of the medium limited to between 2.5 and 3.0), performing a removal of 68% of the remaining dissolved organic carbon. The global dissolved organic carbon removal in this process was of 86% after a membrane filtration step before the photo-Fenton process.