A fluid imaging flow cytometry for rapid characterization and realistic evaluation of microplastic fiber transport in ceramic membranes for laundry wastewater treatment

Microplastics have recently been recognized as emerging contaminants in wastewater, however there is no standardized quantification protocol even though various microscopic approaches exist, many of which are not appropriate for fibrous particles. In this study, a fluid imaging flow cytometry was employed for the first time to quantify microplastic fibers by capturing images, extracting particle parameters, and justifying those parameters with high-speed measurements. We present preliminary results from the high-throughput analysis of microplastic fibers in real laundry wastewater produced at different laundry loads and chemical additives. A bench-scale filtration experiments were conducted to evaluate the performance of silicon carbide and alumina ceramic membranes. Variation in the shape-based volumetric, morphological, and geometrical parameters of each microplastic fiber in the feed and permeate samples were comprehensively compared to evaluate their realistic transport through statistical analysis. Most of microplastic fibers were removed by ceramic membranes when evaluating the retention performance based on the number of units. However, their morphological and geometrical properties had a significant influence on the retention behavior whereby fibers attaining higher curl, lower straightness, and longer geodesic length were better retained due to size exclusion. Interestingly, the circularity of microplastic fibers after both ceramic membrane filtrations was increased due to the shift toward a cylindrical shape with the gradual compression during pressure-driven membrane filtration. These findings provide valuable insights into the advantages and limitations of fluid imaging flow cytometry and represent a significant step in the quantification of microplastics and in clarifying their transport and retention in ceramic membrane-based wastewater treatment.