Humic Acid Transport Research Articles

Combined effects of ferrihydrite coating and ionic type on the transport of compost-derived dissolved organic matter in saturated porous media

Field application of manure compost introduces a large quantity of dissolved organic matter (DOM), which can affect the migration of DOM-associated contaminants. In this study, the transport of humic acid (HA) and compost-derived dissolved organic matter (CDOM) in two porous media under various conditions, including ionic types, ionic strength, and influent concentrations, were investigated by column experiments and modeling analysis. Increasing Na+ concentration did not affect the transport of CDOM and HA in quartz sands, but inhibited CDOM transport in ferrihydrite (Fh)-coated sands. The retention recoveries of CDOM in Fh-coated sands were not changed with increasing NaCl concentration, suggesting that the adsorption of CDOM on Fh-coated sands caused by increasing NaCl concentration was a reversible process. Ca2+ could reduce the mobility of CDOM and HA through bridge bonding and electrostatic interaction. CDOM had a higher mobility than HA in quartz sands under CaCl2 conditions because the aggregation stability of CDOM was stronger than that of HA. The ferrihydrite coating increased the roughness of sand surface, resulting in lower mobility of CDOM in the Fh-coated sands than in quartz sands. A part of CDOM adsorbed onto Fh-coated sand was strongly bound through ligand exchange-surface complexation. The pore volume of CDOM required to saturate adsorption sites onto the Fh-coated sand depends on the influent CDOM concentration. The influent CDOM with higher concentration required less pore volume to achieve adsorption equilibrium. Modeling analysis suggested that the types of deposition sites provided by Fh-coated sand are mainly irreversible sites. Our findings demonstrated that CDOM transport in the sand columns may change the porous medium's physicochemical properties and alter the hydrochemistry conditions. Therefore, these factors mentioned above should not be ignored when evaluating the environmental risks of CDOM.

Water and humic acid transport in graphene-derived membrane: Mechanisms and implications to functional membrane design

Graphene-derived membranes (GDM) have drawn broad attentions due to their superb water permeation and contaminant retention capabilities. In this paper, the transport of model humic acid (HA) and water through GDM is studied using the molecular dynamics simulation approach. By systematically varying the positions of functional groups and membrane pore dimensions, we find that the introduction of functional groups at the slit edge, the basal plane or the interlayer of bilayer graphene nanosheets reduces water permeation through the membranes to significantly different extents. Comparatively, -COO- at the slit edge of GE nanosheet produces the strongest electrostatic interaction for enhanced HA retention and greater water permeability than graphene oxide membranes. Furthermore, HA adsorbed inside GDM may cause membrane fouling due to pore blocking at the slit entrance or pore constriction inside the slit or the interlayer. Meanwhile, the reversibility of membrane fouling depends upon HA desorption, which is easier for HA anchored via functional groups than stacked via π-π interaction onto graphene surfaces. Our findings emphasize that the performance of functional GDM for water treatment is highly dependent upon the specific position of chemical modification, which has been commonly overlooked in previous studies.

Effects of Porous Medium Geochemical Heterogeneity and Divalent Cations on the Transport of Humic Acid

Effects of Porous Medium Geochemical Heterogeneity and Divalent Cations on the Transport of Humic Acid

Humic acid transport in saturated porous media: Influence of flow velocity and influent concentration

Understanding the transport of humic acids (HAs) in porous media can provide important and practical evidence needed for accurate prediction of organic/inorganic contaminant transport in different environmental media and interfaces. A series of column transport experiments was conducted to evaluate the transport of HA in different porous media at different flow velocities and influent HA concentrations. Low flow velocity and influent concentration were found to favor the adsorption and deposition of HA onto sand grains packed into columns and to give higher equilibrium distribution coefficients and deposition rate coefficients, which resulted in an increased fraction of HA being retained in columns. Consequently, retardation factors were increased and the transport of HA through the columns was delayed. These results suggest that the transport of HA in porous media is primarily controlled by the attachment of HA to the solid matrix. Accordingly, this attachment should be considered in studies of HA behavior in porous media.

Humic Acid Transport in Water-Saturated Porous Media

The presence of humic acid (HA) in water poses environmental problems because it enhances the transport of several contaminants. A series of column experiments was conducted toward studying HA transport in different porous media under various pH, ionic strength, and flow rate conditions. The results showed that decreasing pH and increasing ionic strength increased adsorption and therefore delayed the transport of HA in porous media. However, increasing flow rate accelerated the transport of HA in porous media. The effects of pH, ionic strength, and flow rate varied with the solid matrix and were more evident in sands of smaller average particle diameter than in those with larger ones. These factors must be considered when predicting the environmental fate of HA. The results also suggested that HA adsorption was an important process controlling HA transport and should be considered in studies of HA behavior in porous media.