The present work explored the ferromagnetic nanoparticle-seeded polyaluminum chlorides (PACls), and comparatively investigated their coagulation behaviors and magnetic sedimentation efficiency with the commonly adopted magnetic seeding coagulation. Three magnetic PACls were prepared by dosing ferromagnetic nanoparticles Fe3O4 or Fe(0) into the PACl (basicity 1.5) solution. Large clusters of Al species magnetic nanoparticles existed as Al. in the magnetic PACl, exhibiting a colloidal surface configuration, according to the results of Al-27 nuclear magnetic resonance and atomic force microscope. Compared with seeding magnetic nanoparticles into the treating influent, the magnetic PACls could lead to faster floc sedimentation and lower residual turbidity at equivalent doses of ferromagnetic nanoparticles and PACl; meanwhile, the DOC removal efficiency remained almost at the same level. The flocs produced by the superparamagnetic Fe3O4-involved PACl were less resistant for breakage and more difficult to re-form than those derived from the traditionally magnetic coagulation. Thus, after breaking the former flocs in the absence of external magnetic field, those separated magnetic seeds can be recovered via replacing the broken flocs in the magnetic field. Importantly, the mass ratio of magnetic powder to coagulant in the magnetic coagulants was reduced from 10, 67, 100 or even higher to only 1.5-2.5. In sum, with respect to high magnetic separation efficiency, sound DOC removal, and low magnetic powder demand, the magnetic PACl with 50 mg/L Fe3O4 was considered as the preferable coagulant and the related coagulation-magnetic sedimentation process was more robust than the traditionally magnetic coagulation. (C) 2017 Published by Elsevier B.V.