The Role of the Support Layer in Ultrapure Water Filtration Process

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The primary function of the support layer is to prevent filter media from being lost from the water distribution system, and it also plays a role in uniformly distributing the backwash water. When using a high-resistance water distribution system in a single-layer or double-layer filter media tank, the support layer is made of natural pebbles or gravel, with particle size and thickness shown in the table below:

Particle Size and Thickness of Support Layer in High-Resistance Water Distribution System for Rapid Filters

Hierarchy (from top to bottom)	Particle size/mm	Thickness/mm
1	2-4	100
2	4-8	100
3	8-16	100
4	16-32	The height of the layer must be at least 100 mm higher than the orifice of the water distribution system.

In a three-layer filter bed, because the lower layer contains small-sized but heavy-weight filter media, the support layer must be compatible. That is, the upper layer should use heavy ore to prevent the support layer from shifting during backwashing. See the table below:

Three-layer filter bed support layer materials, particle size, and thickness

Hierarchy (from top to bottom)	Material	Particle size,	Thickness/mm
1	Heavy minerals (garnet, magnetite)	0.5–1.0	50
2	Heavy minerals (garnet, magnetite)	1-2	50
3	Heavy minerals (garnet, magnetite)	2-4	50
4	Heavy minerals (garnet, magnetite)	4-8	50
5	gravel	8-16	100
6	gravel	16-32	The height of the layer must be at least 100 mm higher than the orifice of the water distribution system.