Biodegradation of plastic wastes under semi-aerobic condition with active methane oxidation activities and nutrient supply

Elimination of plastic waste deposition in landfills is essential to avoid secondary pollution such as microplastics. Under appropriate environments, methanotrophs which proceed through methane oxidation reaction are capable of degrading plastics via their co-metabolisms. Nevertheless, nutrient conditions in landfills to promote methane oxidation and plastic degradation are still unclear. Therefore, the biodegradation of plastic wastes under semi-aerobic conditions with methane oxidation activities and nutrient additions was examined in this study. Various types of plastics (HDPE, LDPE, oxo-degradable plastics) were exposed to methane and air under semi-aerobic conditions in lysimeters where methanotrophic activities were promoted. Nitrate and phosphate and their combination were introduced into waste mixtures to determine their effect on plastic biodegradation. Changes in gas compositions, plastic weight losses, by-products, and microbial consortium were studied. Phosphate supplement resulted in higher methanotrophic population, particularly that of type I (Methylococcus sp., Methylocaldum sp., Methylovorus sp., Methylomonas sp., and Methylobacter sp.) and yielded highest biodegradation for oxo-degradable (15-20%) followed by HDPE (15-19%), and LDPE (4–7%). The plastic degradation was found well correlated to methane oxidation rate. Oppositely, nitrate supplements reduced MOR due to their competition with oxygen for microbial reactions. Semi-aerobic condition with a phosphate supplement is found effective in promoting plastic degradation in landfills.