Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density epsilon and terminal Reynolds number ReT. The corresponding experiments were performed as a comparison. The clusters of pollutant particles with an inverted "T" structure were observed, the pollutant particles for high epsilon and large ReT scattered wider than that for low epsilon and small ReT. The sedimentation velocities increased suddenly at the initial stage, then decreased drastically, after that swayed around and approached to a steady value. The time to steady state did not depend on epsilon and ReT. The effect of particle interactions was to hinder the average sedimentation velocity, and hindrance was directly proportional to epsilon. The orientation distributions of pollutant particles depended on ReT and epsilon, especially on the former. Both the standard deviations of vertical and horizontal velocity, the former was larger than the latter, were nearly independent on epsilon and ReT.