Review article

This paper considers a model for the deposition of spherical particles in the flow region of a thin-layer module of a wastewater treatment plant. The model takes into account the fluid flow velocity, the inclination angle and roughness of the thin-layer module, as well as the density of the solid and liquid phases. There have been analyzed the forces acting on the particles in the fluid field with continuous uniform flow, balance equation for the forces acting on the particle has been developed, and a calculated dependence for the deposition velocity has been obtained. To assess the state of particles, the concept of equilibrium flow velocity is used, at which the particle reaches a stable state remaining at rest on the plate of the thin-layer module. At a flow rate lower than the equilibrium flow rate there will be a process of sedimentation of particles in the settling tank, and in the reverse situation, there will be particle removal from the structure and reduction of the purification effect. There have been plotted graphs of dependence of equilibrium flow rate on the diameter and density of particles at different angles of inclination of the thin-layer module. The results of the study can be used in engineering practice at developing and optimizing the operation of settling tanks.