Comparison Between Dead End and Cross Flow Filtration

According to the classification of filtering methods, it can be divided into dead-end filtration and cross-flow filtration. Generally, microfiltration uses dead-end filtration, which commonly used filter consumables are High Flow Pleated Filter, Melt Blown Cartridge, String Wound Cartridge; Ultrafiltration uses cross-flow filtration, which commonly used filtration products are PVC Ultrafiltration Membrane Module and PVDF Ultrafiltration Membrane Module. Let's take a look at the difference between dead-end filtration and cross-flow filtration.

Liquid Flow Direction

For dead-end filtration, the liquid flow direction is the same as the filtering direction. Particles larger than the pore size of the filter media in the raw water are trapped on the surface of the filter media, and the liquid and particles smaller than the pore size of the filter media pass through the filter media. For cross-flow filtration, the liquid in the raw water and particles smaller than the pore size of the filter media pass through the filter media. Part of the particles larger than the pore size of the filter media are trapped on the surface of the filter media, and part of the particles are washed away by the water and discharged.

Changes in Liquid Flow

When the dead-end filtration method is adopted, since the trapped particles are not discharged, the filter cake gradually accumulates on the surface of the filter media. As time goes by, the filter cake becomes thicker and thicker until the filter media is completely blocked, and the liquid flow become smaller and smaller. If cross-flow filtration is used, since some of the trapped particles will be washed away by the water flow, compared with dead-end filtration, the filter cake formed on the surface of the filter media is thinner, and the liquid flow rate decreases more slowly.

Pressure on Filter Media

In the process of dead-end filtration, the filter cake on the surface of the filter media will become thicker and thicker with time, and the pressure difference will become larger and larger. It is also necessary to use greater pressure for backwashing. Compared with dead-end filtration, the filter cake formed by cross-flow filtration is thinner, so the pressure difference and the pressure used for backwashing are smaller.

When it comes to filter, which filtering method should we choose? Generally, when the solid content in the raw water is less than 0.5%, in order to reduce energy consumption and save water resources, dead-end filtration is usually used. When the solid content in the raw water is higher than 0.5%, in order to ensure filtration efficiency and prolong service life, cross-flow filtration is usually used.