Biodegradation of low-density polyethylene (LDPE) and starch – based plastic (SBP) by thermophiles Bacillus subtilis and Candida tropicalis

Abstract

This project was carried out to study the biodegradation of low-density polyethylene (LDPE) and starch-based plastics (SBP) by two types of thermophiles microorganisms namely B.subtilis and C. tropicalis in a lab scale method. A few specific objectives were set to identify the growth curve of both strains on LDPE and SBP films, changes in physical and chemical properties by weight loss, carbon dioxide (CO₂) evolved, topography changes of plastics surfaces and the efficiency on biodegradation rate of LDPE and SBP. The results showed that after 49 days incubation period, the optimum growth of B. subtilis for both LDPE and SBP is at week 5 of incubation with 8.9 x 10⁸ CFU/mL and 9.1 x 10⁸ CFU/mL respectively. While for C. tropicalis the highest growth was recorded at week 4 of incubation with 9.6 x 10⁸ for both LDPE and SBP. The weight loss reduction percentage of LDPE and SBP by C.tropicalis was 3.2% and 22.3% respectively while for B. subtilis the results recorded were 4.6% and 12.9% respectively. SEM analysis revealed that there are topography changes for LDPE with bubbling on surface while cracks and holes formed on SBP surface. The strum test used to identify CO₂ evolved in SBP by C. tropicalis is 2.7 g/L which was 5-fold higher as compared to LDPE while in SBP by B. subtilis the results is 2.5 g/L which 5-fold higher compared to LDPE. Based on this study, it can be concluded that C. tropicalis have great potential in degrading SBP as compared to LDPE.