pindfiltratsioon

Pindfiltratsioon, or surface filtration, is a filtration process in which suspended solids are retained near the surface of a porous filter medium, forming a thin solid layer called a cake that contributes to further filtration. The principal mechanism relies on sieving and interception at the surface, with small amounts of particles penetrating slightly depending on the medium.

During operation, feed flows toward the filter medium under pressure or gravity. Particles larger than the pore openings are captured on the surface, gradually building a cake that provides the majority of the filtration barrier. As cake thickness increases, filtration resistance rises, reducing the flow rate. Flows can be run in dead-end mode, where all feed passes through the medium, or in cross-flow where the feed sweeps tangentially along the surface to limit cake buildup. Periodic cleaning, such as backwashing or air scouring, is often required to restore flux.

Materials used include screen, fabric meshes, filter papers, and porous plates, as well as macro- and microfiltration membranes designed for surface capture. Cake properties and pore size, along with feed composition and pressure, determine filtration performance.

Common applications include drinking water treatment, clarification of beverages and juices, pretreatment in chemical processing, sludge dewatering, and certain pharmaceutical purification steps.

Advantages include relatively low equipment cost, the ability to capture relatively large particles, and straightforward operation. Limitations include decreasing flux due to cake buildup, sensitivity to particle compaction, and limited effectiveness for submicron colloids without a supporting depth filter or membrane.