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

Date of publication 10 August 2020

Authors Lapointe, Mathieu; Farner, Jeffrey M.; Hernandez, Laura M.; Tufenkji, Nathalie.

Sources Environmental science & technology : 54 (DocId: 14) 8719–8727.

DOILink https://doi.org/10.1021/acs.est.0c00712

Abstract

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.

TSC Opinion

Les stations d’épuration sont en première ligne pour traiter les eaux usées, en particulier pour enlever les micro plastiques dont les risques pour l’environnement et pour la santé humaine sont en cours d’évaluation. Les technologies classiques de floculation et de coagulation s’avèrent très efficaces pour les micro plastiques qui ont eu un temps de séjour assez long dans l’environnement. Cependant, elles sont relativement inefficaces sur les micro plastiques « neufs ». Ceci est dû au fait que, dans l’environnement, les particules de plastique sont rapidement colonisées par des microorganismes et donc recouvertes d’une matière organique. Les procédés de séparation solide-liquide utilisés dans les STEP sont optimisés pour faire sédimenter la fraction organique particulaire qui est en suspension dans l’eau. Il est donc relativement logique que ce traitement soit efficace sur les micro plastiques colonisés par les micro-organismes. Ceci pose cependant la question des micro plastiques plus jeunes et des techniques à mettre en place pour les éliminer.

Comments area