In the future, upgrading of existing wastewater treatment plants (wwtps) will become the more challenging task than erection of wholly new plants, as most of the plants (e.g. necessary in Germany) do exist already. Since some time, MBR technology has been taken into consideration and has been realised as an alternative for wwtp upgrading. This paper gives an overview about some relevant preconditions, basic upgrading concepts and examples of already upgraded wwtps using MBR technology.