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Isolation and Identification of Native Microorganisms Capable of Biological Degradation of Microplastics and Evaluation of its Performance in the Degradation of These Microplastics

Kashisaz Shahriyar | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56108 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Yaghmaei, Soheila; Ghobadi Nejad, Zahra; Hamzehluoyan, Tayebeh
  7. Abstract:
  8. In recent years, non-biodegradable microplastics (MPs), which cause a lot of pollution in the environment, have become a major concern worldwide. Due to their small size and large surface area, these plastic particles have a great ability to be absorbed into biological cells. Due to their hydrophobic surface, these particles have the ability to absorb pollutants such as heavy metals, toxic medicinal substances, softeners, etc. Microplastics are usually persistent in the environment, allowing them to be transported along the food chain. Research on the degradation of microplastics is focused on biological and non-biological approaches. To date, microorganisms such as algae, fungi, and bacteria have attracted the attention of scientists as a tool to treat microplastic pollution. Polyethylene microplastics are one of the most important microplastics in the environment, which have caused serious pollution in natural environments due to their resistance to biological degradation and the presence of toxic additives. In this study, 16 bacterial strains capable of removing polyethylene microplastics were isolated from 6 microbial sources and their ability to remove this microplastics were evaluated. Among them, the four strains with the best performance were selected, three of which were identified as Achromobacter sp. Ksh2, Bacillus pumilus Ksh3 and Proteus mirabilis Ksh4 based on 16S rRNA analysis. In the continuation of the performance of the combination of these bacteria to remove microplastics in different conditions, the combination of Bacillus pumilus Ksh3 and Proteus mirabilis Ksh4 bacteria showed the best performance. They reduced particle dry weight (31% after 60 days) and average particle diameter (20% after 60 days; obtained by scanning electron microscopy analysis). In the analysis of Energy Dispersive X-Ray Analysis, it was shown that the oxygen and carbon content of treated microplastics increases and decreases, respectively, compared to the control, which indicates the increase in the degradability potential of the treated polyethylene polymers compared to the control. Thermogravimetric analysis showed that the aged particles had a higher thermal stability at temperatures above 600°C compared to the control, thus indicating that the microplastics were degraded by enzymatic chain cleavage, which could in turn lead to a larger resistant fraction of the aged particles remaining at high temperature. Combustion is attributed. Also, by examining the results of Infrared Fourier transform spectroscopy and Scanning electron microscopy, the biodegradation of polyethylene was further confirmed
  9. Keywords:
  10. Polyethylene ; Biodegradation ; Microorganisms ; Microplastics ; Proteus Mirabilis Ksh4 Bacteria ; Achromobacter sp. Ksh2 Bacteria ; Bacillus Pumilus Ksh3 Bacteria ; Pollution Removal

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