Study On Biodegradation Of Diethylene Glycol Terephthalate (DTP) And Polyethylene Terephthalate (PET) Fiber

With the rapid development of PET (Polyethylene terephthalate) and its wide use in industry, there is a substantial fraction by volume added to the waste stream every year, which causes an environmental issue, since PET is highly resistant to atmosphere and biological agents. Therefore, PET waste is a noxious material from global environmental and ecological consideration. Burying or burning methods solving the PET wasters easily cause the pollution of land or air again. Recycling method is limited in practice by its high cost or recycle inconvenient. It is doubtless that the biodegradation is the best way to solve PET and other polymer wastes from the source. But up to now, there is still no effective biodegradation method for the PET wastes in the world.DTP (Diethylene Glycol Terephthalate), as a chemical engineering raw material, is an environmental hormone too. On the other hand, due to the chemical structure of DTP being similar to that of PET, it is one of the best simulating materials to study the biodegradation of PET fiber. Consequently, the study of DTP biodegradation is not only for solving its environmental pollution, but also for developing a foundation for the biodegradability study of the PET.Many sources of activated sludge were collected at different locations of PET fiber factory and Dyeing & Finishing Plant in China. From incubating, cultivating and isolating, 5 strains were screened in the sources. One of the strain, F4, has the most effective degradation for DTP. The optimization of cultivation condition are: M5 Medium, 30°C, pH=7.5, stir frequency 120 r/min.When DTP is degraded by bacteria come from activated sludge, the products are not only TA, but also another compound, because it is not single strain but a lot of in the system. The degradation ratio of DTP after degrading 14 days is more than 92% when pH=7.5, 30°C, and stir frequency 120 r/min. The degradation kinetic of DTP by bacteria and F4 strain accords with Monod equation.The degradation ratio of DTP by Sigma lipase after degrading 24 hours is more than 42% when pH=7.5, 30°C, and stir frequency 120 r/min. When DTP is degraded by Ejn or E_out enzyme that obtained from Strain F4, the degradation radio by E_in enzyme is 10 more times than E_out. And the kinetic parameter K_m (Michaelis-Menten's constant) of E_in enzyme DTP degrading is smaller than Sigma lipase DTP degrading. That means, after domesticating and cultivating, the strain F₄ is suitable for DTP degrading, and E_in enzyme is better than Sigma lipase.After lipase attack at ester bond of a DTP molecule, it did not keep on hydrolyzing the other ester bond of the same DTP molecule at once; instead, it would attack ester bond of other DTP molecule. After accumulating a quantity of the primary hydrolysate, lipase started to hydrolyze the remaining ester bond of the intermediate to form TA. The reaction equation of DTP degraded by lipase followed the expression.Although degradation of PET fiber by microbes, or Sigma lipase, was very weak, from SEM micrographs and HPLC analysis, it has been shown that microbe and lipase can act on PET and cause mill degradation. It can help enzyme absorbing the fiber when fiber has a roughness surface. From HPLC, when rough surface PET fiber is degraded by E_in and E_out enzyme, the TA peak is higher than degraded by microbe T or Sigma lipase. This shows that E_in and E_out enzyme obtained from strain F4 can act on the PET fiber. And it will make a good foundation for the further research.Keywords: Diethylene glycol terephthalate (DTP); Polyethylene terephthalate (PET); Biodegradation; Microbe; Enzyme; Kinetic...