What are membranes in water treatment and their typical applications?

• A. They chemically react with contaminants to neutralize them.
• B. They physically separate contaminants; MF/UF remove particulates and large organics; NF targets multivalent ions and organics; RO removes salts and small molecules; used for drinking water and desalination.
• C. They are only used for wastewater treatment.
• D. They increase turbidity in water.

Answer: (B)

Membranes in water treatment function as selective barriers that physically separate contaminants from water, rather than relying on chemical reactions. Different membrane types have progressively smaller pore sizes, enabling a hierarchy of separation: microfiltration removes particulates and some large organics; ultrafiltration targets smaller organics and colloids; nanofiltration can block multivalent ions and certain organics; and reverse osmosis removes nearly all dissolved salts and very small molecules. Because of this, membranes are commonly used for making drinking water and for desalination of brackish and seawater, as well as for specialized separations in water reuse and industrial processes. They reduce turbidity by removing suspended particles rather than increasing it, and they aren’t limited to wastewater treatment.