Understanding and Improving Microplastic Removal during Water Treatment: Impact of Coagulation and Flocculation

The efficacy of plastic particle removal by municipal water treatment plants is currently uncertain, and the mechanisms involved in microplastic (MP) coagulation and flocculation have only been superficially investigated. The removal of pristine versus weathered plastic debris and the impact of plas...

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Bibliographic Details
Published in:Environmental science & technology 2020-07, Vol.54 (14), p.8719-8727
Main Authors: Lapointe, Mathieu, Farner, Jeffrey M, Hernandez, Laura M, Tufenkji, Nathalie
Format: Article
Language:English
Subjects:
Affinity
Aluminum
Coagulants
Coagulation
Contaminants in Aquatic and Terrestrial Environments
Flocculants
Flocculation
Microbalances
Microplastics
Microspheres
Municipal water
Pests
Plastic debris
Plastic pollution
Polyacrylamide
Polyethylene
Polyethylenes
Polystyrene
Polystyrene resins
Quartz crystal microbalance
Quartz crystals
Surface chemistry
Turbidity
Water treatment
Water treatment plants
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Summary:The efficacy of plastic particle removal by municipal water treatment plants is currently uncertain, and the mechanisms involved in microplastic (MP) coagulation and flocculation have only been superficially investigated. The removal of pristine versus weathered plastic debris and the impact of plastic particle size on removal remain largely unexplored. In this study, coagulation, flocculation, and settling performances were investigated using pristine and weathered MPs (polyethylene (PE) and polystyrene (PS) microspheres, and polyester (PEST) fibers). Weathering processes that changed the surface chemistry and roughness of MPs impacted MP affinity for coagulants and flocculants. A quartz crystal microbalance with dissipation monitoring was used to identify the mechanisms involved during MP coagulation and flocculation. Measured deposition rates confirmed the relatively low affinity between plastic surfaces and aluminum-based coagulants compared to cationic polyacrylamide (PAM). In every case examined, coagulant efficiency increased when the plastic surface was weathered. Removals of 97 and 99% were measured for PEST and weathered PE, respectively. Larger pristine PE MPs were the most resistant to coagulation and flocculation, with 82% removal observed even under enhanced coagulation conditions. By understanding the interaction mechanisms, the removal of weathered MPs was optimized. Finally, this study explored the use of settled water turbidity as a possible indicator of MP removal.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.0c00712