Study on the effect of ionic strength on particle migration and deposition in porous media covered by biofilm based on coupled Lattice Boltzmann method and Discrete element method

Biofilms covering porous media will interact with particles and affect particle migration. In order to investigate the migration mechanism of particles in porous media covered by biofilms, the migration process of particles with different particle sizes under the condition of the changing ionic strength is analyzed by using the lattice Boltzmann method-discrete element method (LBM-DEM) coupling method from mesoscopic scale. The variation patterns of ion strength include gradient and mutation, respectively. Also, the agglomeration of particles at the pore throat in porous media is investigated under different conditions. The main results are obtained as follows. First, both the change of ionic strength and its changing mode significantly affect the migration behavior of particles in NaCl solution but have little effect on the behavior of particles in CaCl2 solution. Second, when the pressure difference between the pressure difference between the inlet and outlet of porous media is 0.4 kPa, the residual permeability of 1.5-mu m particles in the NaCl solution with ionic strength mutation is the highest, which has value of 64.92%. Third, at the specific flow rate, the particles in low ionic strength solution are more likely to be settled. The attraction of particles in the CaCl2 solution is one order of magnitude less than that in the NaCl solution, and the accumulated particles are more likely to be dispersed.