Abstract
The purpose of this paper was to examine the changes in suspended particle size distribution with depth and time during filtration using double filter layer composed of a large artificial semi-cylindrical material in the upper and small quartz sand in the lower. As influent, clay suspension was adjusted to the maximum particle diameter of 70 and 10 μm and the concentration of about 4,600 mg L−1. At elapsed time 60, 120 and 240 min, the amount of the trapped particles in the upper layer, in the boundary between the upper and the lower layer, and in the lower layer was measured. Particle size distributions of the inflow and the outflow suspension, and the trapped particles mentioned above were also measured using laser diffraction scattering particle size distribution analyzer. The results showed the following; (i) in the case of the maximum particle diameter of 70 μm, the main capture site at elapsed time 60 min was the upper layer, but it shifted to the boundary at elapsed time 240 min. On the other hand, in the case of the maximum particle diameter of 10 μm, the capture sites of the sediment were both the upper layer and the boundary at elapsed time 60, 120 and 240 min, (ii) in all cases, the particle size distribution of the suspended particle reaching the lower layer was finer enough to enter the lower layer due to the trapping of the particles in the upper layer and the boundary, (iii) as the coarser part of the suspended particle was trapped in the lower layer, the particle size distributions of outflow suspension were similar to each other, independent f the maximum particle diameter and the elapsed time.
