Enhanced Removal of Polystyrene Microplastics from Water Through Coagulation Using Polyaluminum Ferric Chloride with Coagulant Aids

Microplastics (MPs) pollution has garnered global attention because of its potential risk. The removal efficiencies for MPs in traditional water and wastewater treatment plants are generally low. Coagulation is a widely used process in these facilities. In this study, we investigated the efficiency of three representative coagulation aids, namely, anionic polyacrylamide (PAM), sodium alginate (SA), and active silicic acid (ASA), in facilitating the removal of polystyrene (PS) MPs through the use of polyaluminum ferric chloride (PAFC) coagulation. All three coagulation aids enhanced the removal efficiency of PS MPs. Specifically, ASA demonstrated the highest removal efficiency of 94.28% when used in conjunction with a PAFC concentration of 60 mg/L and a coagulant aid concentration of 10 mg/L. Moreover, the PAFC-ASA system exhibited pH insensitivity, whereas the PAFC-PAM and PAFC-SA systems displayed greater effectiveness under alkaline conditions. The presence of chloride ions (Cl-) had minimal impact on removal efficiency, whereas the presence of sulfate ions (SO42-) hindered coagulation effects in both the PAFC-PAM and PAFC-ASA systems. Furthermore, bicarbonate ions (HCO3-) promoted MPs removal in the PAFC-SA and PAFC-ASA systems but inhibited the effect in the PAFC-PAM system. Based on a comprehensive evaluation of its performance, ASA is suggested as a promising coagulation aid in conjunction with PAFC for the removal of PS MPs.