retentado

Retentado, in the context of filtration and membrane separation, refers to the portion of a feed stream that is retained by the filter or membrane and does not pass into the filtrate or permeate. The term is commonly used in Spanish-language literature and corresponds to the English term retentate. The complementary stream is the filtrate (or permeate).

The composition of the retentado depends on the process and the membrane characteristics. In traditional filtration, it is the solid material accumulated on the filter cake. In membrane processes such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis, the retentado consists of rejected solutes, colloids, macromolecules, and concentrated dissolved species. Its concentration factor increases with process efficiency and selectivity.

Applications of retentados occur across several industries. In water treatment and desalination, retentates are concentrates containing salts and organics; in food and beverage processing, they can be concentrates of sugars, proteins, or flavors; in biotechnology and chemical processing, retentates may contain high-molecular-weight products or assembled complexes.

Handling and disposal are important considerations. Retentados are often discharged, recycled, or subjected to further processing to recover valuable components or reduce waste volume. Decisions depend on regulatory, safety, and economic factors, as well as environmental impact. Operational monitoring typically includes retentate flow rate and volume, total solids, conductivity, pH, and composition to optimize process performance.

See also: filtrate, permeate, membrane filtration, filtration.