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Vermicomposting leads to more abundant microplastics in the municipal excess sludge
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Researchers found that vermicomposting of municipal excess sludge leads to increased microplastic concentrations in the treated material compared to the input sludge, raising concerns that this widely-used organic amendment technology may concentrate and spread microplastic contamination in soils.
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 10 particles ∙kg (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.
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Researchers examined how adding polyethylene microplastic particles to sludge affects vermicomposting performance. The study found that higher microplastic concentrations reduced the efficiency of organic matter removal, impaired composting quality, and caused oxidative stress and neurotoxicity in earthworms, with bacterial diversity also declining in heavily contaminated treatments.
Microplastics identification and quantification in the composted Organic Fraction of Municipal Solid Waste
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Researchers found that mechanical-biological treatment of mixed municipal solid waste generates and concentrates microplastics across multiple processing stages, with the stabilized organic output containing significant microplastic loads — raising concerns about the use of this material as compost or soil amendment.
Microplastics in Sewage Sludge: Changes in Abundance, Size Distribution and Composition During Short and Long-Term Vermicomposting
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Sewage sludge spread on farm fields is a major source of microplastics in soil—and eventually in our food. This study found that using worms to compost the sludge (a process called vermicomposting) initially breaks plastic into more, smaller pieces, but after about a year, worm-processed compost actually had fewer microplastics than sludge that was composted without worms. This suggests vermicomposting could become a practical way to cut microplastic pollution before sludge is used as fertilizer, though it takes patience—the benefits only showed up after long-term processing.
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Researchers tracked microplastic abundance through the vermicomposting stages of sewage sludge — from fresh sludge through aged sludge, vermicompost, and earthworm castings — finding a 52% reduction in microplastic concentration from initial sludge to vermicompost when particles were classified by size, color, and polymer type using micro-Raman spectroscopy.
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