| Textile dyeing sludge,a highly restricted solid waste,is the most emissions as much as the most industrial sludge,the urgent need for effective disposal methods.Dye,containing persistent organic compounds,including polycyclic aromatic hydrocarbons(PAHs),is a key part of the textile dyeing plant and it could easily adsorb in the sludge during wastewater treatment,which will inhibit the subsequent treatment process.Combined ultrasound with Fenton(US-Fenton)technology,as an effective degradation technology,can be used to degrade PAHs,in order to achieve the purpose of harmless.In this paper,the competitions between PAHs during US-Fenton treatment and the products produced during the degradation process were studied to explore the competitive relationship between PAHs and free radicals and degradation pathways of few PAHs.In this paper,the collected sludge samples were extracted to remove a large amount of PAHs and some organic matter,so as to establish a simulated sludge system to remove the influence of other organic pollutants on PAHs degradation experiments.The degradation of PAHs in the simulated system was investigated by US-Fenton technique.The degradation of single PAH and grouped PAHs and the influence of the physicochemical properties of PAHs on the degradation competitiveness were investigated in order to determine competition mechanism.In addition,the degradation mechanism of three PAHs under US-Fenton was deduced by the detection of three PAHs degradation products.Experimental results indicated that:Although some of the organic matter in the simulated sludge system is removed at during pre-treatment,its structure remains similar to that of the original sludge,and it can effectively adsorb PAHs in the study of PAHs competition.The total recoveries of PAHs in simulated sludge system were 79.95%,and the recoveries of 3,4 and 5 rings were 71.80%,79.69% and 88.37%,respectively.In the single experiment,all PAHs were completely degraded at 45 min,and the degradation of PAHs with 3 rings was the fastest.In the grouping experiments,the degradation rates of 3 rings,4 rings and 5 rings were asfollows: Acenaphthene> Fluorene> Anthracene> Phenanthrene,Benz(a)anthracene>Pyrene> Fluoranthene> Chrysene and Benzo(a)pyrene> Dibenz(a,h)anthracene>Benzo(k)fluoranthene> Benzo(b)fluoranthene,respectively.Among them,Acenaphthene,Fluorene,Benz(a)anthracene,Pyrene and Benzo(a)pyrene showed 88.64%,84.87%,82.50%,85.10% and 81.80% removal rates respectively in each group.In the experiment of influences of physical and chemical properties on degradation,it was found that the water solubility and reactivity of PAHs had an effect on its competitiveness.Among them,the water solubility of PAHs affects its availability toward · OH radicals,while the reactivity affects the efficiency and speed of the reaction.On the basis,Acenaphthene and Benzo(a)pyrene were found to have the strongest competition for free radicals during degradation,because Acenaphthene has strong water solubility,while Benzo(a)pyrene has strong reactivity.If the hydrophobicity of Benzo(a)pyrene were to be overcame,it would show a strong competitiveness.During US-Fenton process,the degradation products of Naphthalene,Acenaphthene and Acenaphthylene were detected as quinone,phenolic and acid derivatives.The degradation pathways of Naphthalene,Acenaphthene and Acenaphthylene were obtained,which were divided into two stages.In the first stage of Naphthalene degradation,the occurrence of benzene ring on the H substitution reaction was proposed,and that of Acenaphthene and Acenaphthylene is the occurrence of side chain group oxidation substitution reaction.The second stage of the reaction is quinone chain and complete mineralization.In the US-Fenton system,the phenolic species is added to the Fenton reaction to provide electrons for the trivalent iron ions as an electron transfer media,producing quinones and ferrous ions to supplement the ferrous ions consumed in the reaction,thereby enhancing the reaction. |
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