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Control of Low-Density Microplastics in Wastewater Treatment Plants: The Effects of Process Configuration and Polymer Properties on Removal Efficiency
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Two full-scale wastewater treatment plants achieved over 94% removal of polyethylene microplastics, but removal of polydimethylsiloxane (PDMS) was far more variable due to its high hydrophobicity resisting adsorption to biomass. These findings reveal that certain low-density, hydrophobic polymers common in consumer products are poorly retained by conventional treatment, allowing them to pass into waterways.
The growing concern over emerging contaminants in the urban water cycle has highlighted the role of wastewater treatment plants (WWTPs) as major pathways for their release into aquatic environments. The study investigates the fate of low-density microplastics (MPs) in two full-scale wastewater treatment plants (WWTPs) with moving bed biofilm reactor (MBBR, WWTP-A) and an activated sludge (AS) process coupled with ultrafiltration membrane bioreactor (MBR, WWTP-B). Polyethylene (PE) and polydimethylsiloxane (PDMS) were quantified through a mass-based analytical method using proton nuclear magnetic resonance (1H NMR) spectroscopy. These polymers are characterized by high prevalence in WWTPs influents and low-density characteristics, associated with their abundant presence in final effluents. Both plants exhibited high PE removal efficiencies, averaging 94.9 ± 1.0% in WWTP-A and 97.5 ± 3.5% in WWTP-B, confirming the effective retention of this polymer through WWTP processes. Conversely, PDMS removal resulted in more variable outcomes, with efficiencies of 67.4 ± 22.8% in WWTP-A and 87.8 ± 9.2% in WWTP-B. The lower PDMS removal was attributed to its high hydrophobicity and low surface energy, which hindered adsorption onto microbial biomass and extracellular polymeric substances. The results highlight the importance of design proper technologies for mitigating the discharge of highly hydrophobic polymers into aquatic environments.
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Fate of microplastics in sludge concentration: Experimental evaluation of gravity thickening and flotation processes.
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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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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.
Microplastic Removal in Urban Wastewater: A Systematic Review of Treatment Technologies, Efficiency Determinants, and Environmental Fate
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This systematic review synthesized evidence from 19 studies on microplastic removal technologies in urban wastewater, finding conventional treatment achieves 85-90% removal efficiency primarily through sedimentation, while advanced technologies exceed 90%. A key finding is that most systems redistribute microplastics into sludge rather than eliminating them, raising concerns about land application as a secondary release pathway.
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.
Distribution and removal mechanism of microplastics in urban wastewater plants systems via different processes
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Researchers compared the microplastic removal efficiency of three wastewater treatment technologies and found that the anaerobic-anoxic-oxic process achieved the highest removal rate at 83.9%. Most microplastics were transferred to sludge during primary and secondary treatment stages, with dehydrated sludge containing significant concentrations. The study highlights that while wastewater treatment plants effectively intercept most microplastics, they also redistribute contamination to sludge, which may become a secondary pollution source.
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