Sedimentation characteristics of spherical and rod-like particles in the gravitational field by Brownian dynamics simulations: for the improvement of the visibility of small lakes and ponds

Abstract

From the viewpoint of improving the visibility of water in small lakes and ponds, in a previous study, we treated turbidity-causing (TC) particles and adsorption agents. Brownian dynamics simulations were conducted for particles with a spherical shape in order to elucidate the adsorption performance of the agents in the gravitational field. The technique for the adsorption is based on the use of the translational Brownian motion of the adsorption particles. If non-spherical particles are used as adsorption agents, then rotational Brownian motion is also expected to make a significant contribution to the adsorption performance. In the present study, we have employed the modeling of large spherocylinder adsorption particles and small spherical TC particles with sub-micron size, in order to perform Brownian dynamics simulations in regard to adsorption and sedimentation in the gravitational field. For the case of adsorption particles with a low aspect ratio, the adsorption rate is not significantly different to the spherical particle case, with an improvement of only a few percent. This implies that the rotational Brownian motion hardly contributes to the adsorption performance. In contrast, for the case of a rod-like particle with a high aspect ratio, the adsorption rate is much better than that for the spherical particles, with an improvement of around 75%, and therefore it is seen that the effect of the rotational Brownian motion gives rise to a much more significant adsorption performance. This is mainly because with an increasing aspect ratio the opportunity for the agent particles to contact with the TC particles increases more significantly due to the effect of the rotational Brownian motion. From these results, we understand that rod-like particles with a high aspect ratio employed as adsorption agents are able to adsorb TC substances much more efficiently in comparison to spherical particles.