Enhancement of biodegradation of plastic wastes via methane oxidation in semi-aerobic landfill

• Lysimeters of simulated semi-aerobic landfill were studied for plastic degradation.
• Four types of test plastics were HDPE, LDPE, PP, and PS.
• Highest degraded plastics was enhanced by 1 ml m−1 aeration to the lysimeter.
• Methylocystic sp./Methylocella sp. were functional species in plastic decomposition.

The biodegradation of waste plastics (high/low density polyethylene, HDPE/LDPE; polypropylene, PP; polystyrene, PS) in the simulated lysimeters of semi-aerobic landfill was investigated under different range of aeration rates (1–2 ml min−1) concurrently with a constant rate of a synthetic landfill gas. Methane oxidation was found throughout waste bed of a 1 ml min−1 aerated lysimeter while methane was absolutely oxidized at the bottom of 2 ml min−1 aerated lysimeter. After 3 months of experiment, aeration of 1 ml min−1 gave higher significant percentage losses of weight (15%–20%HDPE and 5%–9%PP) than those of 2 ml min−1 (11%–12%, HDPE and 1%–2%, PP) where high methane oxidation rate (MOR) appeared. Species variety of methanotrophs, heterotrophs, and autotrophs was revealed using PCR-DGGE technique. Only heterotrophs (Burkholderia sp.), nitrifying bacteria (Nitrosomonas sp. AL212, Nitrobacter winogradkyi), Type I methanotrophs (Methylobactor sp. and Methylococcus capsulatus), Type II methanotrophs (Methylocystic sp., Methylocella sp.) were found correlatively to plastics degradation in the lysimeters in different conditions. Many low molecular weight of hydrocarbon compounds such as alkane, alkene, alcohol, acid and epoxide were detected as biodegraded products. In conclusion, biodegradation of plastic wastes in semi-aerobic landfill could be accelerated by supplying an optimum aeration in proportion to methane available in the waste bed.