Impact of Dissolved Organic Matter characteristics and inorganic species on the stability and removal by coagulation of nanoplastics in aqueous media

Abstract

The aggregation of rough, raspberry-type polystyrene nanoparticles (PS-NPs) was investigated in the presence of six hydrophobic and hydrophilic dissolved organic matter (DOM) isolates and biopolymers (effluent OM) in NaCl and CaCl2 solutions using time-resolved dynamic light scattering. Results showed that the stability of PS-NPs mainly depends on OM characteristics and ionic composition. Due to cation bridging, the aggregation rate of PS-NPs in Ca2+-containing solutions was significantly higher than at similar Na+-ionic strength. Biopolymers rich in protein and carbohydrate moieties showed higher affinity to the surface of PS-NPs than the other DOM isolates in the absence of both Ca2+ and Na+. Overall, the stability of PS-NPs followed the order of biopolymers > hydrophobic isolates > hydrophilic isolates in the presence of Na+ and biopolymers > hydrophilic isolates > hydrophobic isolates in Ca2+-containing solutions. In the presence of high MW structures (biopolymers), PS-NPs aggregation in both NaCl and CaCl2 solutions was attributed to steric repulsive forces. The impact of hydrophilic and hydrophobic isolates on PS-NPs aggregation highly relied on the ionic composition. Coagulation was an effective pretreatment for PS-NPs removal. Using inductively coupled plasma-mass spectrometry, higher removals were recorded with Al2(SO4)3 in the absence of DOM, while PACl more efficiently coagulated PS-NPs in the presence of DOM isolates.