Comparison of the Biodegradation of Polypropylene (PP) and Low Density Polyethylene (LDPE) by Pseudomonas aeruginosa and Staphylococcus aureus at Different pH Ranges under Mesophilic Condition

Abstract

The present study aims to assess the temporal variations of some biotic and abiotic biodegradation parameters of 2 polymers (LDPE and PP) by the bacteria P. aeruginosa and S. aureus at acidic, neutral, and alkaline pH under mesophilic conditions. LDPE and PP fragments were immersed in the mineral solutions free of carbon sources containing P. aeruginosa or S. aureus cells. The initial pH values ​​(pHi) of solutions were 5, 7 and 9. Incubation was carried out at 28°C for 10, 20, 30, 40, 50 and 60 days. Results showed that during incubations, the pH of the solutions varies over time. In most cases, the electrical conductivity and cell abundances increased. The weights of the polymers decreased. The cell abundance apparent increasing rates (CAAIR), the electrical conductivity apparent increasing rates (ECAIR), and the polymer weight apparent decreasing rates (PWADR) were estimated. The highest PWADR in the presence of LDPE was 0.4 mg/10days with P. aeruginosaat pHi 5 and 7, and 0.6 mg/10days with S. aureus under pHi 7. For PP, it was constant (0.7 mg/10days) under all pHi with S. aureus, but decreased in the presence of P. aeruginosa with increasing in pHi solutions. The ECAIR with LDPE decreased with increasing pHi with both bacterial species.The highest ECAIR of PP was recorded under pHi 5 with S. aureus and under pHi 7 with P. aeruginosa.The highest CAAIR with LDPE was 185.18 CFU/10days for P. aeruginosa at pHi 5 and 116.79 CFU/10days for S. aureus at pHi 7. With PP, it was 297.61 CFU/10days for P. aeruginosa at pHi 5 and 67.64 CFU/10days for S. aureusat pHi 7. The biodegradation parameters values recorded with of P. aeruginosa differed significantly (P<0.05) from those recorded with S. aureus under each pHi.