Modular filter system comprising: - a first termination module, - a second termination module and - a plurality of filter modules arranged between the first and second termination module (70, 80), each comprising: ∘ a filter element with ▪ at least one filter medium separating a filtrate side from a retentate side of the filter element, and ▪ a filter medium support on which the filter medium is attached and which at least has one support inlet channel and at least one support discharge channel, ∘ a first filter cassette part with at least one first cassette inlet channel and at least one first cassette discharge channel, ∘ a second filter cassette part with at least one second cassette inlet channel and at least one second cassette discharge channel, the filter medium support being fluid-tightly arranged in an arrangement position between the first filter cassette part and the second filter cassette part, the at least one support inlet channel being fluidically connected to the at least one first cassette inlet channel and the at least one second cassette inlet channel in order to form a module inlet channel, the at least one support discharge channel being fluidically connected to the at least one first cassette discharge channel and the at least one second cassette discharge channel in order to form a module discharge channel, the module inlet channel being fluidically connected to the retentate side of the filter medium and the module discharge channel being fluidically connected to the filtrate side of the filter medium; the module inlet channel of the at least one filter module being fluidically connected to a fluid inlet of the first and/or second termination module (70, 80) and the module discharge channel of the at least one filter module being fluidically connected to a fluid discharge of the first and/or second termination module (70, 80); characterized in that the filter system further comprises: - a first filter module, - a second filter module, and - a separation module which closes the module inlet channel of the first filter module in the direction of the second filter module, fluidically connects the module discharge channel of the first filter module to the module inlet channel of the second filter module and closes the module discharge channel of the second filter module in the direction of the first filter module. - a first termination module, - a second termination module and - a plurality of filter modules arranged between the first and second termination module (70, 80), each comprising: ∘ a filter element with ▪ at least one filter medium separating a filtrate side from a retentate side of the filter element, and ▪ a filter medium support on which the filter medium is attached and which at least has one support inlet channel and at least one support discharge channel, ∘ a first filter cassette part with at least one first cassette inlet channel and at least one first cassette discharge channel, ∘ a second filter cassette part with at least one second cassette inlet channel and at least one second cassette discharge channel, ∘ a filter element with ▪ at least one filter medium separating a filtrate side from a retentate side of the filter element, and ▪ a filter medium support on which the filter medium is attached and which at least has one support inlet channel and at least one support discharge channel, ▪ at least one filter medium separating a filtrate side from a retentate side of the filter element, and ▪ a filter medium support on which the filter medium is attached and which at least has one support inlet channel and at least one support discharge channel, ∘ a first filter cassette part with at least one first cassette inlet channel and at least one first cassette discharge channel, ∘ a second filter cassette part with at least one second cassette inlet channel and at least one second cassette discharge channel, - a first filter module, - a second filter module, and - a separation module which closes the module inlet channel of the first filter module in the direction of the second filter module, fluidically connects the module discharge channel of the first filter module to the