Study On The Degradation Method And Mechanism Of Polycyclic Aromatic Hydrocarbons In Oily Sludge Based On Laccase Reverse Micelle System

Polycyclic aromatic hydrocarbons?PAHs?are hydrocarbons composed of two or more benzene rings combined and are widely found in nature and in equilibrium degradation.Due to the development of society,more and more emissions have brokenthe balance,and the pollution to the environment has become increasingly serious.The degradation of polycyclic aromatic hydrocarbons in oily sludge has become the focus of attention.Laccase is a polyphenol oxidase containing four kinds of copper ions in the catalytic center.The product of laccase reaction is water.It is an environmentally friendly catalyst and it has been widely used in the chemical industry.Reverse micelle,a nano-scale polymer,formed in an organic solvent when the surfactant concentration exceeds the critical micelle concentration possesses thermodynamic stability and exhibits a spontaneously transparent appearance.The surfactant in the reverse micelle system consists of two parts:a hydrophilic group and a hydrophobic group.Hydrophilic groups accumulate in the polar nucleus,which can keep a part of the water forming a"pool"in which polar molecules can dissolve.The activity of laccase is susceptible to external factors.Therefore,this"pool"structure in the reverse micelle system protects laccase from organic solvents and the external environment.At present,the degradation of polycyclic aromatic hydrocarbons in oily sludge based on laccase-reverse micelle system is rarely reported.In this study,an ultraviolet spectrophotometer was used to detect phenanthrene,anthracene,benzo?a?anthracene and benzo?b?fluoranthene in oily sludge.Replacing the oil in the oily sludge with isooctane,using cetyltrimethylammonium bromide as the surfactant,and n-hexanol as the cosurfactant to obtain the reverse micelle.The best water content W₀ is 10by measuring the conductivity of the system.Under these conditions,the effects of pH,temperature and ionic strength on the degradation rate of PAHs were studied.The results showed that the laccase activity was highest at pH 4.2,temperature 30?,and KCl concentration 60 mmol/L.After 24 hours,the degradation rates of phenanthrene,anthracene,benzo?a?anthracene and benzo?b?fluoranthene were 50.3%,68.2%,51.2%and 68.9%,respectively.At the same time,compared with that of non-immobilized laccase,the ratio between the secondary structures of laccase under different conditions was studied.The secondary structure of the enzyme protein includes alpha-helix,beta-sheet,beta-turn and random coil.The experimental results showed that when pH=4.2,temperature30? and KCl concentration was 60 mmol/L,the structure of?-helix accounts for the largest proportion,and the ratio of?-helix in the laccase secondary structure in the laccase-reverse micelle system was higher than that of the non-immobilized laccase secondary structure.Finally,the process of laccase degradation of polycyclic aromatic hydrocarbons was simulated by Gaussian 09 and the energy barrier of each carbon atom and the total of each polycyclic aromatic hydrocarbon molecule in yttrium,phenanthrene and benz?a?anthracene was calculated by the possible intermediates energy.The benz?a?anthracene was used as substrate to detect the intermediates that may occur during the degradation process by gas chromatography-mass spectrometry.Based on these intermediates,the possible binding sites and degradation pathway of laccase and benzo?a?anthracene were presumed.