Filtration is a common technique for mechanically separatinggases or liquids. A filter membrane serves as a barrier to enable ion exchange, removing macromolecules or bacteria from solution, separating colloids, or recovering gases. Some uses for filtration include producing clean drinking water, generating safe food products, and ensuring a clean environment. It is used for petro-chemical vapor recovery, oxygenation of blood in an artificial lung, and hemodialysis via an artificial kidney. Filter membranes are necessary for ion exchange in a fuel cell and for electrolysis. Filtration is also a key procedure in the laboratory to separate RNA, DNA, cells, proteins, and other molecules.