The role of mobile-immobile sorbents on flow and colloid-facilitated contaminant transport through porous media: Two-dimensional modeling

A mathematical model based on conceptual equilibrium has been devised to study the role of mobile-immobile sorbents on colloid-facilitated contaminant transport through a two-dimensional, saturated, and homogeneous groundwater system with transient flow conditions. The primary drawback of the kinetic model arises from its inability to handle the large number of parameters involved in multi-dimensional regions at bigger scales when several transport processes and transient flow conditions are included. In order to prevent model complexity, the current study is the first attempt to investigate the equilibrium approach with transient flow conditions in a two-dimensional domain. Conventionally, colloids enhance the contaminant transport by adsorbing contaminants through multiple sorption reactions. However, it was noticed that even in the presence of colloids ($C_c=100mg/l$), BTCs get attenuated due to an increase in $k_3$, which indicates a stronger affinity of pollutants with the static solid matrix. Therefore, the present study suggests that the mere existence of colloids may not guarantee enhanced contaminant movement. A contaminant plume with 50 mg/l of colloids travels 2 m ahead of the contaminant without colloids, and this distance increases to 4.7 m for 100 mg/l colloids. Therefore, colloids can either be favorable in the case of contaminated aquifer rehabilitation or adverse in the event of groundwater contamination spread.