Degradation of the herbicide paraquat by photo-fenton process: optimization by experimental design and toxicity assessment

Abstract

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 ...

Treatment of Effluent from a Factory of Paints Using Solar Photo-Fenton Process

“…Only a slight improvement in COD removal was observed when increasing the H 2 O 2 concentration from 1600 up to 2500 mg L −1 , respectively, 70 to 57 mg O 2 L −1 , probably due to the formation of acids of low molecular weight, refractory to oxidation [33,34]. Similar behavior was observed for DOC removal (Figure 1(a)) and for the absorption maxima at 224 and 272 nm (Figure 1(b)).…”

“…On the other hand, for an H 2 O 2 concentration of 2500 mg L −1 , the reduction of toxicity was from 100 to 23% (Figure 3). It is probable that this effect is related to the formation of carboxylic acids, that tend to be toxic to A. salina [33], as also reported in studies involving Daphnia magna in the degradation of sulfamethoxazole and amoxicillin [37,38].…”

Degradation of the antibiotic chloramphenicol by photo-Fenton process at lab-scale and solar pilot plant: Kinetic, toxicity and inactivation assessment

“…The accumulated UVA radiation per liter of solution in the photo-Fenton experiments, carried out in both reactors was calculated as described by Trovó et al (2013a). An accumulated UVA radiation 6 times higher than that provided by solar radiation to the CPC reactor (5.3 kJ L À1 ) was provided by the high pressure mercury lamp in the lab-scale reactor (31.7 kJ L À1 ) in an equivalent irradiation time (60 min).…”

Biodiesel Wastewater Treatment by Coagulation-Flocculation: Evaluation and Optimization of Operational Parameters

“…Positive coefficients of the combination of the variables concentration of Al 3+ and treatment time suggest a synergistic effect, while negative coefficients, correspond to an antagonistic effect. [21][22][23] Analyzing equation 1, the linear positive coefficient equal to +0.03 for Al 3+ indicates that high concentrations of this coagulant favor the turbidity removal. Although negative, the quadratic coefficient is quite low (-0.00006), meaning a very small influence on the net effect.…”