RESUMO
An experimental and theoretical study of the UV spectrum of chlorothalonil (CT) was carried out and the vibrationally resolved HOMOâLUMO transition is presented for the first time. The fluorescence spectrum has also been recorded. Furthermore, preparative photolysis allowed a detailed study of the photoproducts formed with recognition of different isomers. In the presence of oxygen only the first reductive dechlorination-decyanation occurred, while in its absence a successive dechlorination-decyanation takes place.
Assuntos
Nitrilas/efeitos da radiação , Oxigênio/química , Fotólise/efeitos da radiação , Teoria Quântica , Raios Ultravioleta , Recuperação e Remediação Ambiental , Fungicidas Industriais/efeitos da radiação , Halogenação , Nitrilas/químicaRESUMO
Imazalil (IMZ) is a widely used fungicide for the post-harvest treatment of citrus, classified as "likely to be carcinogenic in humans" for EPA, that can be only partially removed by conventional biological treatment. Consequently, specific or combined processes should be applied to prevent its release to the environment. Biological treatment with adapted microorganism consortium, photo-Fenton, and coupled biological photo-Fenton processes were tested as alternatives for the purification of water containing high concentration of the fungicide and the coadjutants present in the commercial formulation. IMZ-resistant consortium with the capacity to degrade IMZ in the presence of a C-rich co-substrate was isolated from sludge coming from a fruit packaging company wastewater treatment plant. This consortium was adapted to resist and degrade the organics present in photo-Fenton-oxidized IMZ water solution. Bacteria colonies from the consortia were isolated and identified. The effect of H2O2 initial concentration and dosage on IMZ degradation rate, average oxidation state (AOS), organic acid concentration, oxidation, and mineralization percentage after photo-Fenton process was determined. The application of biological treatment to the oxidized solutions notably decreased the total organic carbon (TOC) in solution. The effect of the oxidation degree, limited by H2O2 concentration and dosage, on the percentage of mineralization obtained after the biological treatment was determined and explained in terms of changes in AOS. The concentration of H2O2 necessary to eliminate IMZ by photo-Fenton and to reduce TOC and chemical oxygen demand (COD) by biological treatment, in order to allow the release of the effluents to rivers with different flows, was estimated.
Assuntos
Fungicidas Industriais/química , Imidazóis/química , Consórcios Microbianos/fisiologia , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/química , Biodegradação Ambiental , Embalagem de Alimentos , Fungicidas Industriais/metabolismo , Fungicidas Industriais/efeitos da radiação , Imidazóis/metabolismo , Imidazóis/efeitos da radiação , Oxirredução , Fotólise , Poluentes Químicos da Água/metabolismo , Poluentes Químicos da Água/efeitos da radiaçãoRESUMO
The photodegradation of chlorothalonil, a polychlorinated aromatic fungicide widely used in agriculture, was investigated under ultraviolet-visible irradiation in the presence and absence of different humic substances that significantly enhance the chlorothalonil phototransformation. On the basis of a kinetic model, an analytical study, the effect of scavengers, the chlorothalonil phosphorescence measurement, and varying irradiation conditions, it was possible to demonstrate that this accelerating effect is due to their capacity to reduce the chlorothalonil triplet state via H-donor reaction and to energy transfer from the triplet humic to ground state chlorothalonil. Energy transfer occurs at wavelengths below 450 nm and accounts for up to 30% of the reaction in deoxygenated medium upon irradiation with polychromatic light (300-450 nm). This process is more important with Elliott humic and fulvic acids and with humic acids extracted from natural carbonaceous material than with Nordic NOM and Pahokee peat humic acids. The obtained results are of high relevance to understanding the processes involved in chlorothalonil phototransformation and the photoreactivity of humic substances. Chlorothalonil is one of the rare molecules shown to react by energy transfer from excited humic substances.
Assuntos
Transferência de Energia , Substâncias Húmicas/análise , Luz , Nitrilas/efeitos da radiação , Fotólise/efeitos da radiação , Ar , Fungicidas Industriais/química , Fungicidas Industriais/efeitos da radiação , Cinética , Nitrilas/química , Oxigênio/química , Solo , Soluções , Raios UltravioletaRESUMO
Photocatalytic degradation of phenylmercury was studied using TiO2 in aqueous suspension assisted by UV-A irradiation. Reaction conditions, such as pH and amount of TiO2 were set using a factorial design of experiments resulting in a greater influence of pH on phenylmercury degradation. Hg (II) reduction and simultaneous oxidation of aromatic group was observed. Optimum reaction conditions were obtained under nitrogen atmosphere at pH 10 and 0.35 g/L(-1) TiO2. Under these conditions almost 100% reduction of mercury was reached after 30 min UV irradiation. Total mercury reduction was achieved after 40 min reaction under saturated oxygen. Furthermore, phenol and diphenylmercury were identified as intermediate products of oxidation. It was observed that a major fraction of the reduced mercury was removed as metallic vapor by gas stripping, whereas a minor fraction was adsorbed on the catalyst surface, probably as Hg(OH)2. Under optimal conditions obtained by multivariable analysis, total mineralization of organic matter was achieved after about 60-min irradiation.