A Comparative Study of the Biodegradation of High-Density Polyethylene (HDPE) and Polyethylene Terephthalate (PET) by Selective Bacteria

Kong, Penny Pui Nee (2025) A Comparative Study of the Biodegradation of High-Density Polyethylene (HDPE) and Polyethylene Terephthalate (PET) by Selective Bacteria. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Plastics, such as High-Density Polyethylene (HDPE) and Polyethylene Terephthalate (PET), are widely used due to their durability and low cost, but their extensive use has led to environmental pollution and microplastic accumulation. Addressing this pollution is crucial due to its impact on ecosystems and human health. This study aims to evaluate the ability of Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli, and Staphylococcus aureus to biodegrade HDPE and PET which provides valuable insights into bioremediation strategies. Bacterial hydrophobicity was determined using the Bacteria Adherence to Hydrocarbon (BATH) method, followed by a shake flask method to assess plastic biodegradation. The plastic films were incubated with different bacterial populations, with the plastic film being the sole carbon source for the bacteria. The plastic surface protein content, reflecting biofilm formation, was analyzed by Bradford test, and the weight loss (%) was measured to evaluate biodegradability. Additionally, Fourier-Transform Infrared (FTIR) spectroscopy was used to identify changes in the chemical structure of the plastic films after bacterial exposure. S. aureus showed the highest hydrophobicity (45.33 ± 0.59%), followed by P. aeruginosa and B. subtilis, with E. coli having the lowest (10.53 ± 1.19%). The protein content was higher on PET and at 37°C, leading to increased weight loss on PET and under the 37°C condition. The study showed that P. aeruginosa, B. subtilis, and S. aureus degraded plastic more effectively than E. coli, as indicated by weight loss (%). B. subtilis and S. aureus exhibited the greatest degradation of HDPE (0.19%), whereas P. aeruginosa demonstrated the highest PET degradation (0.32%). FTIR analysis revealed new functional groups and intensity changes indicating the action of the enzyme on the plastic film. However, the specific enzymes responsible for degradation were not identified. Future research could focus on identifying these enzymes to support sustainable plastic waste management solutions.