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Mesophilic anaerobic digestion of mixed sludge in CSTR and AnMBR systems: A perspective on microplastics fate

Journal of Environmental Management 2025 11 citations ? Citation count from OpenAlex, updated daily. May differ slightly from the publisher's own count. Score: 58 ? 0–100 AI score estimating relevance to the microplastics field. Papers below 30 are filtered from public browse.

L. Borrás, A. Seco, J.A. de Ferrer, María Lera, N. Martí, J. Serralta

Summary

Researchers compared how two types of anaerobic digesters used in wastewater treatment affect the fate of microplastics in sewage sludge. They found that while digestion reduced some types of microplastics, it also fragmented larger particles into smaller ones, and a membrane bioreactor retained more microplastics than a conventional stirred tank. The study suggests that current wastewater treatment processes may not fully eliminate microplastics and could even create smaller, harder-to-remove particles.

Polymers

PAN PE PP

Study Type Environmental

Most microplastics (MPs) end up in the biosolids produced in wastewater treatment plants (WWTPs) and can pose contamination risks when the biosolids are applied to agriculture. This study evaluated the impact of mesophilic anaerobic digestion on the fate of MPs in WWTP sludge. For this, two laboratory-scale anaerobic digesters were operated in parallel, consisting of a continuous stirred tank reactor (CSTR) and a membrane bioreactor (AnMBR) equipped with an ultrafiltration membrane to decouple the hydraulic and sludge retention times. Both digesters were continuously fed with mixed sludge from a municipal WWTP. The results showed a significant reduction in the MP concentration, with the AnMBR having the higher MP removal efficiency (88.6% vs. 62.1%) and obtaining a higher percentage of biomethanisation (58.3% vs. 43.7%). Polypropylene (PP) and polyacrylonitrile were the main polymers in the mixed sludge, while PP and polyethylene were the dominant polymers in the digested samples. The MP particles in all the samples were predominantly in the 500-104 μm size range. Microbiological analysis indicates a greater species diversity in the microbial community of the AnMBR, the results also revealed a symbiotic relationship between the Firmicutes and Patescibacteria phyla in this digester.

Mesophilic anaerobic digestion of mixed sludge in CSTR and AnMBR systems: A perspective on microplastics fate

Summary

Discussion