A filter unit includes membrane plates placed together parallel to one
another, which at least in zones around connecting elements for the
purpose of draining permeate are connected together liquid-tight. The
membrane plates because of their shape and after two membrane plates have
been placed one on top of the other are provided for manufacturing a
liquid-tight connection or a seal by welding. As a result unfiltered
liquid flows through between the membrane plates and contamination of the
permeate within a volume situated between the connecting elements is
prevented. Over a number of connecting elements and zones located in
between it is possible to attach a hollow profile, which is closed-off at
its ends. This hollow profile in a liquid-tight manner surrounds
discharge openings of the connecting elements and the zones located in
between with positive material engagement. As a result, a permeate
collection channel is formed, out of which and through a permeate
discharge the permeate can be extracted through suction.