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Fate of microplastics in sludge concentration: Experimental evaluation of gravity thickening and flotation processes.
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This study was the first to systematically evaluate how microplastics behave during sludge concentration processes in wastewater treatment, finding that polymer density and operational conditions strongly influence their distribution between liquid and solid phases. Up to 64% of low-density HDPE was released into the clarified stream during gravity thickening, while high-density PTFE remained entirely in the clarified water during dissolved air flotation.
Microplastics (MPs) are commonly retained in the sludge line of wastewater treatment plants (WWTPs), yet their behaviour during sludge concentration processes remains poorly understood. This study is the first to systematically evaluate MPs distribution in sludge concentration processes, revealing the critical role of polymer density and retention time. MPs behaviour was evaluated in gravity thickening and dissolved air flotation (DAF) using real sludge samples doped with three polymers of contrasting densities: HDPE, PET, and PTFE. MPs were quantified in both liquid and solid phases through oxidative digestion and Raman spectroscopy. Results showed that up to 64 % of HDPE was released into the clarified stream during gravity thickening, while PET and PTFE remained mostly in the sludge. In DAF, 63 % of HDPE was recovered in the floated sludge, whereas 100 % of PTFE was found in the clarified water. These findings highlight the influence of polymer properties and operational conditions on MPs separation and suggest that sludge concentration units can play a key role in enhancing MPs removal prior to final sludge management.
More Papers Like This
Fate of microplastics in sludge concentration: Experimental evaluation of gravity thickening and flotation processes.
AI summary Read the abstract
This study investigated microplastic distribution during sludge concentration processes at wastewater treatment plants, finding that polymer density and retention time critically determine particle fate during gravity thickening and dissolved air flotation. Up to 64% of low-density HDPE was released into clarified water during gravity thickening, while denser polymers remained in the sludge phase.
Fate of microplastics in sludge concentration: Experimental evaluation of gravity thickening and flotation processes
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Researchers tracked microplastics through two common wastewater sludge treatment processes — gravity thickening and dissolved air flotation — finding that polymer density strongly determines where plastics end up, with lighter HDPE escaping into wastewater streams while heavier particles stayed in sludge, suggesting these steps could be targeted for early microplastic removal.
Fate of microplastics in wastewater treatment plants and their environmental dispersion with effluent and sludge
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Researchers tracked microplastics through a wastewater treatment plant and found 12 different polymer types in effluents and sludge, with smaller particles (25–104 μm) most abundant and fibres displaying lower sizes than fragments. The study demonstrates that WWTPs do not fully remove microplastics and that processed sludge marketed as soil amendment carries plastic contamination.
Behavior and flow of microplastics during sludge treatment in Japan
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Sampling of two Osaka wastewater treatment plants found microplastics at every stage of the sludge treatment process, with 13 polymer types identified; concentration increased through dewatering, but the total MP load in final biosolids was lower than in raw sludge.
Research Progress on Occurrence, Removal and Fate of Microplastics in WWTPs
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Wastewater treatment plants (WWTPs) are a major route by which microplastics reach rivers and oceans, yet they also remove a substantial portion of incoming particles. This review synthesizes data on microplastic abundance, shape, size, and polymer type across WWTP influent, effluent, and sludge, finding that fibres become proportionally more dominant in effluent while PP, PE, PA, and PET dominate throughout. Understanding WWTP performance is critical because sludge applied to farmland and treated effluent discharged to waterways both represent significant ongoing sources of microplastic contamination.
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