Vermicomposting leads to more abundant microplastics in the municipal excess sludge

• Published in: Chemosphere (Oxford) Vol. 307; no. Pt 3; p. 136042
• Main Authors: Cui, Guangyu, Lü, Fan, Hu, Tian, Zhang, Hua, Shao, Liming, He, Pinjing
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2022
• Subjects: activated sludge; Biodegradation; Biowaste; cost effectiveness; digestion; Eisenia fetida; electron microscopy; Fourier transform infrared spectroscopy; gizzard; microplastics; Microplastics pollution; polyethylene; soil; temperature; Vermicomposting; vermicomposts; Biodegradation; Microplastics pollution; Vermicomposting; Biowaste; Eisenia fetida
• ISSN: 0045-6535; 1879-1298; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.136042

Municipal excess activated sludge is not only an important reservoir of microplastics particles, but is also a vehicle of entry of microplastics into the environments as soil amendments or organic fertilizer. Vermicomposting is a cost-effective technology for sludge valorization. However, it is not clear whether vermicomposting affects the occurrence of microplastics in residual sludge. Here, the variation of microplastics (0.05–5 mm) in sludge, including the abundance, type, size, and morphology, before and after vermicomposting by epigeic earthworms under different temperature conditions (15 °C, 20 °C and 25 °C) were investigated by micro Fourier Transform Infrared Spectroscopy (μ-FTIR) and Scanning Electronic Microscopy (SEM). More abundant (over 104 particles ∙kg−1 (dry weight)), and smaller microplastics (over 60% in total with 0.05–0.5 mm) in the treated sludge via earthworms were observed compared to the raw sludge. The increment of vermicomposting temperature was more obvious (p < 0.05) for the enrichment of the microplastics, especially for polyethylene particle. Gizzard grinding and microbial digestion in the gut of earthworms may contribute to the fragment of microplastics. The present study suggests that the sludge-sourced vermicompost is still an important hotspot of microplastics, posing a potential threat to the receiving environments. [Display omitted] •More abundant and tiny microplastics detected in the vermicompost.•Temperature influenced the abundance of microplastics in the vermicompost.•Gizzards' grinding and biodegradation may cause the increase of microplastics.•Sludge-sourced vermicompost is still an important hotspot of microplastics.