Experimental study into the sedimentation process of solids of different origin

Abstract

Sedimentation refers to the first stage of wastewater treatment from mechanical impurities. Its rate depends on the density and particle size of impurities, as well as the density and viscosity of dispersion medium. In industrial sedimentation tanks, particle settling can occur in laminar, transient or turbulent modes. Aim. To establish the criterion equations and their coefficients for sedimentation processes of sand, glass and polyamide granules. Sedimentation of sand particles of 0.001– 0.003 m, spherical glass particles with the diameter of 0.0025–0.004 m and polyamide granules with the volume-surface mean diameter of 0.0022–0.003 m was carried out in a measured glass cylinder filled with distilled water. Each solid particle was measured, then, it came into contact with the water surface by means of tweezers, and released, starting to settle to the bottom of the cylinder under the action of gravity. A stopwatch was used to time the particle passaging between the marks of the measured cylinder. Calculations were performed using dimensional analysis. According to the test results, the dependences of the Reynolds number on the Archimedes number were established for the sedimentation of sand particles and polyamide granules in the transient mode, while spherical glass particles in the turbulent mode. In addition, the criterion equations of the solid particles sedimentation in the liquid were derived. The coefficients for these equations were experimentally determined. The equations and coefficients obtained in the study can be used in the design of settling tanks for mechanical treatment of wastewater to remove sand, glass and polymer particles.