Microbial consortium involving biological methane oxidation in relation to the biodegradation of waste plastics in a solid waste disposal open dump site

• Biodegradation of waste plastics in simulate lysimeters of open dump was studied.
• Four plastics were tested: HDPE, LDPE, PP, PS.
• Highest kinetics decay rate (K) was of HDPE, but the lowest K was of LDPE.
• High plastic decay rate was found where high methanotrophic activity appeared.
• Correlation of plastic biodegradation kinetics rate and MOR is an exponential.

The simulated lysimeters of an open waste dump were employed to investigate microbial consortium in relation to the biodegradation of waste plastics (high/low density polyethylene, HDPE/LDPE; polypropylene, PP; polystyrene, PS). A low flow rate of a synthetic biogas was purged continuously to imitate methane oxidation. The plastics were examined periodically for chemical composition and microbial consortium. The PCR-DGGE and FISH techniques revealed bacterial consortium such as heterotrophs, autotrophs and methanotrophs colonizing simultaneously on the waste plastics. Only methanotrophs tended to increase with time throughout the waste bed, particularly for type I/II methanotrophs (Methylobacter sp./Methylocella sp.). Some microbes were found only at a 15 cm depth such as Methylococcus capsulatus, Acinetrobacter spp., and Flavobacteria spp. Biodegradation of waste plastics in terms of weight loss, chemical changes and surface deterioration clearly occurred where there was a high density of methanotrophs on the waste plastics. Methanotrophs functioned as the principal decomposer in plastic biodeterioration particularly in the upper zone of the lysimeter. The highest kinetic decay rate was of HDPE (K, 0.128 y−1) whereas the lowest K (0.048 y−1) was of LDPE. In summary, the waste plastics were biodegraded in the simulated lysimeters which yielded a good correlation between plastic degradation kinetics and rate of methane oxidation.