The understanding of the fate and the transport of carbon nanotubes (CNTs) in the water treatment process will provide important information for assessing the environmental risks of CNTs. To fill the knowledge gap, this study investigated the removability of multiwalled carbon nanotubes (MWNTs) stabilized by humic acid (HA) during the coagulation-flocculation-sedimentation (CFS) process. The structure characteristics of the produced flocs were systematically investigated using a variety of characterization approaches. The configuration resembling a root-soil system is shown in the images of scanning and transmission electron microscopy (SEM and TEM). With the incorporation of HA-MWNTs into the produced flocs, the X-ray diffraction (XRD) patterns of MWNTs completely disappeared. Fourier transform infrared spectra (FT-IR) and Mossbauer spectra suggested that the intervention of HA-hinged MWNTs increased the degree of polymerization and the particle size of the produced hydrous ferric oxide (HFO). Finally, both the effective sequestration of MWNTs by CFS demonstrated here and the high sorption capacity of MWNTs for phenanthrene implied that MWNTs might be used as a potential coagulant aid in water processing for the enhanced removal of hydrophobic organic chemicals. (C) 2011 Elsevier Inc. All rights reserved.