Influence of humic acid and bovine serum albumin on colloid-associated heavy metal transport in saturated porous media.

Colloid-facilitated contaminant transport in porous media has been widely observed in laboratory and field studies. In this study, the influence of two dissolved organic matters (DOMs), humic acid (HA) and bovine serum albumin (BSA), on the colloid-associated heavy metal transport, was investigated. Soil colloids with particle sizes <2 μm were prepared from bentonite. Glass bead was used as porous media for the column tests. The influence of DOM on the adsorption of Pb and Cu onto colloids was tested. Colloid mobility and colloid-metal co-transport in the presence/absence of DOMs were investigated by breakthrough tests. The test results showed that DOMs facilitated colloid mobility. The measured ζ-potentials showed that DOMs enhanced the electrostatic repulsion between colloids and glass beads and reduced colloid deposition. These findings were further confirmed by calculating the interaction energy using the DLVO theory. Batch tests showed the strong adsorption of Pb and Cu on the colloid, and the adsorption was enhanced by DOMs. The colloid-metal co-transport tests showed that colloids can significantly facilitate the transport of Pb and Cu and that the facilitation was further enhanced by DOMs. By heavy metals, the colloid mobility was retarded, mainly due to the increased deposition. The transport of Cu facilitated by DOM was more obvious than that of Pb. Compared to BSA, the effect of HA on enhancing colloid mobility, increasing colloid adsorption to heavy metals, and hence on the facilitation of colloid-associated heavy metals transport was more prominent.