filtrables

Filtrables is a term used to describe the fraction of a mixture that can pass through a given filter under specified conditions. In filtration practice, a mixture is separated into a filtrate, the material that passes through the filter, and a retentate, the material retained by the filter. The term filtrables specifically refers to components that are smaller than the filter's pore size or are otherwise able to traverse the filter medium by mechanisms such as diffusion or convective flow.

Filtrability depends on pore size and the physical properties of the components, including size distribution, shape, and interactions with the filter material. Filtration processes are categorized by nominal pore sizes or membrane classes: microfiltration roughly 0.1 to 10 micrometers, ultrafiltration about 2 to 100 nanometers, nanofiltration around 1 to 2 nanometers, and reverse osmosis achieving effective separations near molecular dimensions below about 0.1 nanometers. The filtrable fraction can change with pressure, temperature, and flow configuration (dead-end versus cross-flow).

Applications of assessing filtrables include water and wastewater treatment, where dissolved salts or small colloids are filtrable through membranes at certain stages; food and beverage processing, for clarifying liquids; pharmaceutical manufacturing, for sterilizing-grade filtration; and analytical chemistry, where filtrability determines sample preparation steps.

Limitations of relying on filtrability include membrane fouling, concentration polarization, and selectivity limits that can alter the composition of the filtrate over time. Understanding filtrability helps design filtration steps, choose appropriate media, and optimize operating conditions.