Sand filtering mechanism

The structure of the filtration pond consists of a "filtered sand layer" that filters to remove fine suspended matter, and there is a "support layer" covered with gravel under it. The gravel support layer of the gravel serves to keep the filtered sand from flowing out. Underneath it is a "water collection device" that collects filtered water.
In this way, fine clumps (flocks) of turbid components that could not be removed by the sinking pond are removed from top to bottom.

Compared to the gap between the sand particles in the filter sand, most of the flocs flowing into the filtration pond is about 1 to 10 minutes of 25 minutes, and is large enough to pass through the filter sand gap.
In other words, rapid filtration not only squeezing large particles in narrow gaps, but also removes small flocs by adsorption on sand particles.
For this reason, if the inflowing turbid components are not lumps (not floced), most of them will flow out of the filtration pond, so in rapid filtration, by injecting a coagulant in the sinking pond before filtration. It is important to flock the turbid components.
Mechanisms of aggregation Sinkden