Enhanced removal of polyethylene terephthalate microplastics through polyaluminum chloride coagulation with three typical coagulant aids

Highlights: • Coagulant aids can effectively promote microplastics removal. • ASA removed 54.70% PET MPs at conventional dosage, followed by SA and PAM. • PAM removed 91.45% PET MPs under high dosage, followed by ASA and SA. • Coagulant aids enhanced the effect of adsorption and sweep flocculation. • Enhanced coagulation systems are highly adaptable based on experimental results. Given the discovery and hazard of microplastics in freshwater environments, the removal of microplastics in drinking water deserves more attention. Nevertheless, in the light of existing literature, the effectiveness of conventional coagulation on microplastics removal is insufficient. Hence, enhanced coagulation is worth being explored. This study investigated the improving performance of anionic polyacrylamide (PAM), sodium alginate (SA), and activated silicic acid (ASA) when using poly‑aluminum chloride (PAC) to remove polyethylene terephthalate (PET) microplastics. The experimental results showed that ASA had the highest removal efficiency (54.70%) under conventional dosage, while PAM achieved the best removal effect (91.45%) at high dosage. Mechanism of coagulation was studied by scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR), X-ray photoelectron spectroscopy (XPS), and the results illustrated that when only PAC existed or the dosage of coagulant aids was low, double layer compression was the main principle. The increase of coagulant aids dosage improved the effect of adsorption and sweep flocculation significantly. Moreover, jar tests carried in different conditions demonstrated that the current coagulation systems were highly adaptable.