Modeling the transport of sodium dodecyl benzene sulfonate in riverine sediment in the presence of multi-walled carbon nanotubes.

The environmental risks of carbon nanotubes have received considerable attention. In this work, the effects of multi-walled carbon nanotubes (MWCNTs) on the adsorption of sodium dodecyl benzene sulfonate (SDBS) by riverine sediment and the transport of SDBS in sediment were studied. MWCNTs could significantly increase the adsorption capacity of the sediment for SDBS, thus affecting the transport of SDBS in sediment. Maximum adsorption capacity of the sediment for SDBS increases from 2.29 to 2.99 mg/g with the increasing content of MWCNTs from 0% to 1.5%. Breakthrough curves (BTCs) of SDBS obtained from the column experiments were described by the convection-dispersion equation, Thomas model, and Yan model. The estimated retardation factor R increases with the incorporation of MWCNTs, either in water or sediment. Additionally, the value of R is well correlated to the content of MWCNTs in sediment. Compared with Thomas model, Yan model is more suitable for fitting the BTCs with all the values of R ≥ 0.951, but it tends to overestimate the maximum adsorption capacity when the content of MWCNTs in sediment is relatively higher. The results of SDBS retention in sediment indicate that MWCNTs can increase the accumulation of SDBS in the top sediment layer, while they can impede the transport of SDBS into deeper sediment layer when incorporated into the sediment. These effects should be taken into consideration for risk assessment of CNTs in the aquatic environment.