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Intensive use of engineered nanoparticles (NPs) results in their release into aquatic systems and consequently into drinking water resources. Therefore, it is important to evaluate how NPs can be effectively removed through water treatment processes, such as coagulation, to control environmental and health risks associated with NP exposure. This work investigates the effect of two conventional coagulants, polyaluminum chloride (PACl) and iron chloride (FeCl3), on NPs. Three bottled mineral and Lake Geneva waters, currently used as drinking water resources, were considered to get an insight into coagulation efficiency. TiO2, CeO2 NPs, and polystyrene (PS) nanoplastics were selected, owing to their large number of applications and contrasting surface charge and aggregation behavior at environmental pH. Our findings indicate that PACl is more efficient compared with FeCl3 since lower dosages are required to coagulate all nanoparticles. On the other hand, nanoplastic coagulation is found less efficient compared with TiO2 and CeO2 NPs. This is an important outcome indicating that nanoplastic stability and dispersion state will be more pronounced and therefore more challenging to eliminate. Results highlight the key role of NP and PS nanoplastic surface charge, as well as water properties, coagulant type, and dosage on nanoparticle elimination from aquatic systems. Practitioner Points pH, water hardness, and NOM are playing roles in final coagulant dosage concentration. PACl is more efficient than FeCl3 in most conditions. Positively charged nanoplastics are more difficult to eliminate by coagulation. NP surface properties in bottled mineral and surface waters are controlled by pH, divalent cations, and NOM. NP surface charge and coagulation efficiency depend on water properties.

The coagulation of negatively charged polystyrene latex micro-plastic particles is studied in presence of two linear biopolymers (chitosan and sodium alginate) and a trivalent salt, aluminum chloride as coagulants. The performance of the different coagulants, impact of the solution pH, and use of alginate as a coagulant in presence of aluminum chloride, fractal character and compactness of aggregates are investigated by using mainly electrophoretic experiments and image analysis. The coagulant efficiency and coagulation routes and strategies are analyzed by considering the variations of the particle surface charges at variable coagulant concentrations.Optimal coagulant dosage is determined when the surface charge of the latex particle is neutralized.Our results suggest that the biopolymers are in some cases more efficient than AlCl3 for the destabilization of latex micro-plastic particles. Indeed, charge neutralization is more rapidly achieved by chitosan regarding the optimal dosage and chitosan is found to work over a wider range of pH values. Alginate is also found to be a good candidate when particle charge inversion is achieved first with aluminum chloride. We also demonstrate that coagulant dosage is dependent on the initial pH of the suspension. When the initial pH of the dispersion is low, the isoelectric point is obtained for small dosage values. Image analysis indicates that in all situation fractal aggregates are obtained and that biopolymers result in the formation or more compact structures which will increase the sedimentation rates.

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