Abstract:

The occurrence of microplastics (MPs) during anaerobic and aerobic treatment processes of kitchen waste was investigated using case studies from the prominent waste treatment facilities of Shanghai Liming Resources Recycling Co., Ltd. and Shanghai Wenxin Biotechnology Co., Ltd. The presence of MPs in the resulting organic fertilizers and the agricultural soils fertilized with these products were further tracked to reveal the pollution characteristics and environmental fate of MPs. Results showed that MPs were present in both anaerobic and aerobic kitchen waste treatment processes, primarily as transparent or black fibers under 1 mm in size and composed predominantly of polyethylene terephthalate (PET) or Rayon. Before anaerobic treatment, the average abundance of MPs in the samples ranged from 40.0 to 546.7 items/kg, whereas, after treatment, the average abundance of MPs in the biogas slurry and biogas residue decreased significantly by 75.53% and 54.41%, respectively. The average abundance of MPs in waste and rice husks before aerobic treatment ranged from 53.3 to 493.3 items/kg and 66.7 to 566.7 items/kg, respectively, whereas, that in organic fertilizers was increased by 46.84%. The average abundance of MPs in the soil with organic fertilizers was (176.7 ± 34.8) items/kg, which was 137% higher than that of the soil without organic fertilizers. These results indicate that MPs can be produced in the process of municipal food waste treatment, and the pollution of soil MPs can be exacerbated through organic fertilizers.

Key words: microplastics, kitchen waste, soil, waste treatment, organic fertilizers