the latter in detail the plasma generation device 22 may comprise electrodes as plasma generation means 26 28 at the secondary side of the membrane 12 whereas the plasma generation device 24 may comprise electrodes as plasma generation means 30 32 at the primary side of the membrane 12 the electrodes are in this case connected to a voltage source being part of the plasma generation device 22 24 in order to apply a voltage between the electrodes and thus to generate the plasma 18 20 like shown in fig1 however it may as well be possible to generate the plasma based on capacitive excitation based on inductive excitation or based on electromagnetic waves for example in case of capacitive excitation the plasma generation device 22 24 may comprise a voltage source creating a alternating electrical field between two capacitor plates as plasma generation means 26 28 and or 30 32 the capacitor plates may be arranged behind a separator 34 36 38 40 in order to separate the plates from the respective gas stream the separator 34 36 38 40 may be formed of glass for example consequently no direct contact of the plasma generation device 22 24 or its plasma generation means.