a method of adding or removing a gas to or from a solution of the gas in a liquid involves transferring the gas between the liquid and another fluid through a membrane unit . the membrane unit includes a membrane which is substantially impermeable to the solvent and having a permeability to oxygen of at least 100 barrers ; formed from an amorphous copolymer of perfluoro - 2 , 2 - dimethyl - 1 , 3 - dioxole ; and is maintained at a temperature below the glass transition temperature of the copolymer . the fluid can be another liquid or a gas . the novel method provides very high rates of gas transmission between liquids and permits gasifying liquids without resort to sparging bubbles through the liquid . the method thus can gasify liquid with superior efficiency and without excessive agitation due to bubbling . these features result in economy of gas consumption and reduced need for gas recovery equipment , and when used in connection with a toxic or organic gaseous component , reduced requirements for additional pollution control equipment . the membrane material is resistant to fouling by liquids , and especially , by bioreactor mass . hence , the novel method can remain in service for long duration without substantially diminished performance . utilities for the novel method include purifying drinking water through ozonolysis , oxygenating bioreactors and blood ; oxidizing volatile organic compounds in water ; adding gaseous reactants to liquid chemical reactions and supplying oxygen to and removing volatile pollutants from waste water .