Abstract
Wastewater treatment plants (WWTPs) contribute to the release of significant quantities of microplastics into the aquatic environment. The facile identification of microplastics and an understanding of their occurrence and transport through WWTPs are essential for improving microplastic retention. Potential microplastic treatment technologies for both polymeric and ceramic membrane filtrations were systematically investigated to inform decisions on the optimal choice of membrane for effective microplastic retention. A blocking filtration model, based on a simple linear regression fitting, was used in experiments on the filtration of microplastic suspensions to determine the relative importance of individual fouling mechanisms. Unlike the commonly applied spectroscopic techniques, the facile identification approaches, that are closely related to the amounts of particles within wastewater samples, attempted to identify tiny microplastics (<1.0 μm) by comparing them against silica particles for reference. A larger decline in the normalized permeate flux was observed for 0.1 μm polystyrene microplastics, while standard pore blocking appeared to be the dominant fouling mechanism for all membranes. More microplastics based on turbidity and total solids were removed using the ceramic membrane than the other polymeric membranes. However, fewer microplastics, based on the particle size distribution analysis, were removed using the ceramic membrane as the pore size measurements gave a relatively large pore size for the ceramic membrane, compared with other polymeric membranes; even though a nominal pore size of 0.1 μm for all membranes were provided by the suppliers. The contribution of microplastic-containing synthetic wastewaters to overall flux decline was significantly greater than those of identical microplastic suspensions because of the aggregation of larger microplastics with dissolved organic matter in synthetic wastewater, leading to the formation of a cake layer on the membrane surface. Despite the challenges associated with the facile identification approaches, our findings provided deeper insights and understanding of how microplastics behave in membrane filtration, which could enable the application of potential microplastic treatment technologies.