A two-way coupled model for the co-transport of two different colloids in porous media.

Models for the co-transport of two different colloids commonly assume a one-way coupling. This is because often a large colloid and small colloid are involved. Therefore, they assume that the spread of smaller colloid is affected by the transport of larger colloids, but not the other way around. However, a number of studies have shown that this assumption is not valid, even for large and small colloids. Therefore, in this study, a two-way coupled model is developed to simulate the co-transport of two different colloids in porous media and their effect on each other. We have considered the interactions of the two colloids with the grain surface, kinetics of heteroaggregation (of the two colloids), and heteroaggregate deposition onto the grain surface. We assumed a first-order kinetic model to represent heteroaggregate formation and its deposition on the grain surface. The model is evaluated by fitting the experimental data reported in four different papers from the literature on the co-transport of clay colloids and viruses, bacteria and graphene oxide nanoparticles, and clay colloids and graphene oxide nanoparticles. The model performance is compared with the commonly-used one-way coupled model. The two-way coupled model is found to satisfactorily simulate most of the experimental conditions reported in the above papers, except for the co-transport of montmorillonite-adenovirus, and Staphylococcus aureus- graphene oxide nanoparticles.