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Microplastics Removal in a Dynamic Coagulation-Flocculation-Sedimentation System
Summary
Researchers compared microplastic removal during standard jar tests (batch) and continuous-flow flocculation systems, finding that flocculation mechanisms and removal efficiency differed significantly between the two setups. Conventional jar testing may overestimate microplastic removal because the flow conditions in real treatment plants are different. These findings have direct implications for designing more effective microplastic removal in full-scale water treatment facilities.
Most studies examining microplastics (MPs) removal during bench-scale trials have applied sweep flocculation, such that the impact of other coagulation mechanisms remains largely unknown. Furthermore, the use of bench-scale batch systems (e.g., jar testing), wherein the hydrodynamics bear little resemblance to their full-scale counterparts, is ubiquitous in the literature. In this study, MPs removal during jar tests and bench-scale continuous-flow trials was compared. The production of large aluminum hydroxide floc consistent with sweep flocculation was the dominant factor driving MPs removal. Under combined coagulation and sweep flocculation conditions, total MPs removal was lower (11 – 82%) during continuous-flow trials, suggesting that extrapolation of jar test results may overpredict removal in full-scale systems. Strong correlations were observed between MP concentration and turbidity reduction, indicating that it may potentially serve as a surrogate. As well, correlations were observed when comparing both floc size and concentration to the removal of MPs.