Microplastic (MP, < 5 mm) and nanoplastic (NP, < 1 µm) pollution has become a growing environmental concern, as they are detected everywhere, including in surface waters used for drinking water (DW) production. Recently, NPs have been detected in finished DW, indicating incomplete removal by DW treatment plants (DWTPs). Coagulation-flocculation-sedimentation (CFS) is a promising treatment technique, but current research lacks connection to practice and/or mostly focuses on MPs. This thesis investigates the influence of coagulant type, dose, and NP size on NP removal during CFS. The research connects to practice by using coagulants and doses used in the Dutch DWTPs.

A survey with four Dutch DW companies provided insight into the CFS procedures. Jar tests simulated CFS in the lab, using ferric chloride (FeCl₃), aluminium chloride (AlCl₃) and polyaluminium chloride (PAC) to assess the impact of coagulant types. Theoretical optimum doses were compared to practical doses (obtained from survey) to determine the influence of the coagulant dose. Lastly, the effect of NP sizes on CFS removal efficiencies was studied using 200, 500, and 1000 nm NPs. All experiments were done with NPs spiked in tap water. CFS efficiency was evaluated through turbidity, pH, alkalinity, UV-VIS, residual coagulant and ζ-potential measurements.

PAC was identified as the most efficient coagulant considering all evaluated parameters. Theoretical doses, which were higher than practical doses for FeCl₃ and AlCl₃, achieved more effective NP removal than practical doses. Charge neutralisation was confirmed as the main mechanism for NP removal. Lastly, although particle size is generally thought to affect NP removal, this study’s results did not allow for confirmation or refutation of this statement. Overall, this research highlights that the type of coagulant and dose can influence NP removal in DWTPs. These findings can be a first step to help DWTPs optimise CFS for more NP removal.