a process for treating sewage containing biological solids including the steps of mixing the sewage with oxygen - containing hydro fluoro ether polymers , retaining the sewage with the hydro fluoro ether polymers for a desired period of time so as to produce oxygenated sewage and carbon dioxide - containing hydro fluoro ether polymers , and separating the carbon dioxide - containing hydro fluoro ether polymers from the oxygenated sewage . water is separated from the oxygenated sewage so as to produce a sludge . oxygen is mixed with the carbon dioxide - containing hydro fluoro ether polymers so as to oxygenate the hydro fluoro ether polymers and to remove carbon dioxide therefrom . the sewage is retained with the hydro fluoro etherpolymers at a temperature of between 32 ° and 140 ° f . the sewage is dewatered prior to mixing so that the dewatered sewage has a water content of less than 93 percent by weight . the steps of mixing and retaining can be carried in a closed vessel . the hydro , fluoro ether polymers can be an emulsion containing perfluoro - bis - chlorobutyl ether .