Coagulation-based Physicochemical Removal of Polyester and Polypropylene from Wastewater: Impact of Experimental Conditions and Colloidal Charges

Abstract

Microplastics (MPs) have been identified as a global environmental and health threat due to their existence in diverse ecosystems. The level of exposure to these unregulated emerging contaminants defines the potential harm to the environment and public health. Several treatment technologies have been used to remove MPs from wastewater. However, the existing treatment technologies have failed to achieve complete elimination of MPs and require additional energy and cost. This study focused on removing MPs from simulated wastewater using iron chloride (FeCl₃) coagulation. Jar test experiments were conducted to determine the removal efficiency of target MPs polyester (PEST) and polypropylene (PP). Zeta potential (ZP), Fourier Transform Infrared (FTIR), and Scanning Electron Microscopy (SEM) techniques were used to investigate the PEST and PP removal mechanism. The removal efficiency for both types of MPs was influenced by various experimental conditions, including pH, dosage of used coagulant, settling time, and stirring speed. The highest removal efficiencies for PEST and PP at the optimum dosage of FeCl₃ (4.57 mg/L) and pH (7) were 95 ± 1.10% and 61.50 ± 1.32%, respectively. However, these removal efficiencies slightly declined to 91 ± 1.00% for PEST and 59.50 ± 1.00% for PP when the coagulant dosage was increased to 5 mg/L, which showed that charge inversion occurred at a high dosage. The mechanisms for removing MPs were identified as charge neutralization and adsorption. This was demonstrated by the SEM images that agglomeration and adsorption occurred in the PEST/PP and coagulant system. The ZP changes and elemental confirmation by FTIR spectra further confirmed the formation of new bonds during the interaction between PEST/PP and FeCl₃. This study presents a potential solution by providing an effective and efficient technology for MP removal from synthetic wastewater. However, it is of significant importance to replicate this in real-world wastewater problems and further research.