Membrane filtration methods

There are two types of membrane filtration systems commonly used: 1) dead-end filtration, and 2) cross-flow (tangential flow) filtration.

Dead-end filtration filters the entire feed supplied to the membrane, which is the same method as conventional sand or paper filtration. The filter membrane requires periodic rinsing or replacement because the target material for separation accumulates on the membrane surface. Meanwhile, cross-flow filtration performs filtration by passing the feed parallel to the membrane. The parallel flow reduces the number of suspended substances and colloids in the feed that accumulate on the membrane.

The filtration method is closely connected to the quality of raw water, the material and separation performance of the membrane, module structure, rinsing method, etc., and needs to be properly selected based on treatment conditions.

In terms of costs, dead-end filtration requires less power cost compared to cross-flow filtration, which needs to form parallel flow but requires rinsing or membrane replacement at relatively short intervals. In cross-flow filtration, faster flow along the membrane surface results in less accumulation of foulant on the surface and thus faster flux. Higher flux along the membrane surface is more desirable for controlling accumulation but requires higher power costs. Therefore, the flux should be designed so as to be economically based on the relationship between the amount of water to be treated and the washing effect.

Cited from Japan Water Research Center, “Membrane Filtration in Water Supply, with Q&A, Glossary of Filtration Methods in Water Supply” (partially modified)