Transport of emerging organic ultraviolet (UV) filters in ceramic membranes: Role of polyethylene (PE) microplastics.

Microplastics can be considered potential carriers of emerging organic ultraviolet (UV) filters due to their considerable adsorption capacity in wastewater treatment. The adsorption behavior of organic UV filters, which are commonly contained in personal care products to preserve the skin against UV radiation, onto polyethylene (PE) microplastics were systematically studied to investigate their combined effects. Kinetics and isotherm analyses revealed that the adsorption of four organic UV filters onto PE microplastic surfaces followed a multi-rate and a heterogeneous multi-layer pattern. Several factors including salinity, microplastic size, and dosage also influenced the adsorption efficiency due to hydrophobic interactions. A bench-scale cross-flow ceramic membrane filtration experiment was investigated to evaluate the role of PE microplastics on the retention performance of organic UV filters. The retentions for organic UV filters were 34.2%-37.8% in the non-existence of PE microplastics. Conversely, organic UV filter retentions were significantly increased up to 82.2%-97.9% when they were adsorbed onto the PE microplastics, which were almost completely retained by the ceramic membrane. Therefore, organic UV filters can likely migrate and eventually be carried by PE microplastics, thus increasing the retention of both emerging organic UV filters and microplastics prior to discharge from wastewater treatment facilities.

Engineered Approaches to Facile Identification of Tiny Microplastics in Polymeric and Ceramic Membrane Filtrations for Wastewater Treatment.

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.