A single use filter module capable of on-line production of a medical fluid which is sterile, non-pyrogenic, and free from cytokine-inducing substances, comprising a) a housing comprised of a1) a bottom part comprising a fluid compartment and a fluid outlet positioned on the center line of the bottom part at one end of the fluid compartment; a2) a top part comprising a fluid compartment and a fluid inlet positioned on the center line of the top part 2 on one end wall of the fluid compartment; and b) a positively charged microporous flat sheet membrane arranged within the housing, characterized in that i) the bottom part contains, in the fluid compartment, a support structure consisting of a plurality of longitudinal ribs and transversal ribs; ii) the top part contains, in the fluid compartment, a support structure consisting of a plurality of longitudinal ribs and transversal ribs; iii) a protection net is arranged within the housing and located atop the longitudinal ribs of the bottom part; iv) the positively charged microporous flat sheet membrane is located atop the protection net; and v) a retention net is arranged within the housing and located between the positively charged microporous flat sheet membrane and the longitudinal ribs of the top part. a) a housing comprised of a1) a bottom part comprising a fluid compartment and a fluid outlet positioned on the center line of the bottom part at one end of the fluid compartment; a2) a top part comprising a fluid compartment and a fluid inlet positioned on the center line of the top part 2 on one end wall of the fluid compartment; and a1) a bottom part comprising a fluid compartment and a fluid outlet positioned on the center line of the bottom part at one end of the fluid compartment; a2) a top part comprising a fluid compartment and a fluid inlet positioned on the center line of the top part 2 on one end wall of the fluid compartment; and b) a positively charged microporous flat sheet membrane arranged within the housing, characterized in that i) the bottom part contains, in the fluid compartment, a support structure consisting of a plurality of longitudinal ribs and transversal ribs; ii) the top part contains, in the fluid compartment, a support structure consisting of a plurality of longitudinal ribs and transversal ribs; iii) a protection net is arranged within the housing and located atop the longitudinal ribs of the bottom part; iv) the positively charged microporous flat sheet membrane is located atop the protection net; and v) a retention net is arranged within the housing and located between the positively charged microporous flat sheet membrane and the longitudinal ribs of the top part. i) the bottom part contains, in the fluid compartment, a support structure consisting of a plurality of longitudinal ribs and transversal ribs; ii) the top part contains, in the fluid compartment, a support structure consisting of a plurality of longitudinal ribs and transversal ribs; iii) a protection net is arranged within the housing and located atop the longitudinal ribs of the bottom part; iv) the positively charged microporous flat sheet membrane is located atop the protection net; and v) a retention net is arranged within the housing and located between the positively charged microporous flat sheet membrane and the longitudinal ribs of the top part.