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Effects of polymer type and photoaging of microplastics on co-adsorption of atrazine and bisphenol A and cake layer partitioning during microfiltration of surface water
Summary
Tiny plastic particles in water can grab onto common pollutants like bisphenol A (BPA, found in plastics) and atrazine (a weed killer), essentially acting like magnets that carry these chemicals through water treatment systems. This study found that the type of plastic, how "weathered" it is, and water conditions (like salt levels) all affect how tightly these chemicals stick together and whether standard water filters can catch them — meaning water treatment plants may need to adjust their methods to fully remove these combined contaminants before water reaches your tap.
Microfiltration is widely applied for surface water purification; however, the coexistence of microplastics (MPs) and organic contaminants in source waters of varied salinity and natural organic matter (NOM) may influence contaminant partitioning and fouling behavior during filtration. This study investigates how polymer type (i.e. polyethylene (PE) and polyethylene terephthalate (PET)) and aging of MPs affect their interactions with mixed contaminants, transport and partitioning of the contaminants in cake layer during microfiltration under varying salinity and NOM. PE-MP and PET-MP exhibited a stronger adsorption affinity toward bisphenol A (BPA) than atrazine (ATZ). Density functional theory calculations confirm noncovalent-dominated adsorption on PE-MP and π-π interactions governing adsorption on PET-MP. Aging alters such interactions by modifying surface physicochemical properties, leading to differential adsorption behavior compared to pristine MPs. Increasing ionic strength enhanced BPA adsorption via a salting-out effect (P < 0.05) but suppressed ATZ adsorption, while Suwannee River fulvic acid showed negligible influence due to competitive sorption. Microfiltration experiments demonstrated that polymer type, aging state, operating pressure, and water chemistry jointly regulate MP cake structure, thereby controlling contaminant transport, partitioning, and specific cake resistance. PE-MP and PET-MP held negative surface charge at zeta potentials of -18.07 and -6.39 mV in feed water, respectively. Polymer properties and aging-induced surface modifications governed the transition between interaction-driven fouling and mechanical compaction, which is increasingly important at elevated trans-membrane pressure. Moreover, hetero-aggregation between organic contaminants and MPs alleviated hydraulic resistance. These findings provide mechanistic insights for optimizing membrane processes to improve the removal of MP-associated contaminants.