A review of sources, fate, effects, and management of microplastics in sewage sludge

Microplastics (MPs) accumulate at high concentrations in sewage sludge. Upon sludge disposal, MPs are continuously released into the environment, driving cross-media migration and posing risks to ecological and human health. This review synthesizes the sources and occurrence characteristics of MPs in sludge, their migration and transformation during wastewater and sludge treatment, and their migration, accumulation, and environmental effects from post-treatment sludge disposal. Industrial wastewater, domestic sewage, and stormwater runoff are the primary sources of MPs, with fibrous particles being the most prevalent in sludge. During wastewater treatment, only a minute fraction of MPs is discharged into the receiving waters with the treated effluent. In contrast, the vast majority is retained and ultimately accumulates in the sludge. During sludge treatment, these particles undergo secondary fragmentation and show increased hazard potential, leading to long-term environmental accumulation and ecological impacts via sludge disposal pathways. Moreover, MPs can enter the food chain, posing potential threats to human health. To address these risks, this paper proposes a whole-chain prevention and control strategy, spanning from source reduction to end-of-pipe measures. This approach shifts from passive management to proactive, process-wide regulation of MPs in sludge, offering theoretical foundations and technical references for pollution control in sewage sludge. • Domestic, industrial, and runoffs are key sources of microplastics (MPs) in sludge. • Wastewater treatment transfers most MPs to sludge; removal varies by stage. • Sludge treatment fragments and ages MPs, increasing potential toxicity. • Sludge disposal releases MPs, posing ecological and human health harms. • Source-to-end control: source cuts, process upgrades, and regulated reuse monitoring.