Roles of magnetic particles in magnetic seeding coagulation-flocculation process for surface water treatment

Magnetic seeding coagulation-flocculation (MCF) process was evaluated by jar tests compared to a reference coagulation-flocculation (CF) process. Steps were made toward elucidating the underlying roles of magnetic particles (MPs) in MCF process. The results indicated that MPs addition could significantly accelerate flocs sedimentation and enhance pollutants removal. With an optimal strategy of adding the composite PACl/MPs (MPACl, 15/30 mg/L) first followed by 0.4 mg/L PAM, turbidity, UV254 and TP were removed up to 96.7%, 80.8% and 95.7% in 5 min under applied magnetic field (0.5 T). In addition, the multifunction of MPs reduced the negative impacts of pH changes, resulting in a wider working pH range. Humic acid-like components adsorbed on MPs and MPs-Al species improved the UV254 removal in MCF process than that in CF process. For low turbidity water, MPs increased suspended particles concentration and served as nuclei to enhance the formation of settleable flocs, consistent with an increase in turbidity removal from 89.75% to 96.80%. The multiple roles of MPs (suspended particles, adsorbents and coagulants) in MCF process were thoroughly discussed. This study provides theoretical guidance for its application in real surface water treatment.