Fate and dynamics of microplastics in the municipal waste composting process

BACKGROUND AND OBJECTIVES: This study demonstrates stage-specific changes in microplastic abundance and polymer composition throughout composting, highlighting process-based reduction and fragmentation dynamics as a novel contribution from Indonesia. The study aimed to explore the dynamics of microplastic presence throughout the composting process of municipal waste and to evaluate the effectiveness of composting in mitigating microplastic contamination in compost derived from municipal waste.METHODS: Sampling was conducted during five consecutive stages of composting at the Galuga landfill composting facility. The stages included three-week fermentation material, dried products, shredded material, grinded material, and compost products ready for sale. The extraction and identification techniques followed standardized protocols. The study integrated biological digestion and density separation methods, implementing rigorous measures to reduce cross-contamination.FINDINGS: A total of 5042 microplastic particles were identified from approximately 25 kg of samples, yielding an average abundance of 201.53 ± 14.02 particles per kilogram. Microplastic concentrations exhibited no notable variations between samples gathered during the wet and dry seasons. A progressive reduction in microplastic levels was detected from the initial stage to the final outcome. The presence of larger microplastics (>2000 micrometers) diminished from the initial stages to the finished product, whereas smaller microplastics (200 to 1000 micrometers) increased from the beginning to the compost product. Fragments were noted as the most widespread shape of microplastics, predominantly resulting from mixed waste packaging. Eight different types of polymer groups were identified, with polyethylene, polypropylene, and polystyrene being the most prevalent, comprising 72.10 percent.CONCLUSION: The results indicate evident stage-specific variations in the occurrence of microplastics throughout the composting process of municipal waste. The abundance of microplastics consistently decreased from initial materials to the final compost product, with significant reductions noted after the shredding and grinding stages. Even though larger fragments were prevalent throughout all phases, the proportion of smaller particles rose as the larger ones fragmented during the composting process. The polymer types dominated in this research reflect the high presence of food packaging in the incoming waste stream. This emphasizes the potential of composting as a mitigation approach and the critical need for enhanced upstream waste separation and more stringent regulations to decrease plastic inputs into composting systems.