Modules for electrodeionization apparatus

A modular cell for use in an electrodeionization apparatus, the cell comprising an electrically inert disk-shaped spacer having a central hub and upper and lower surfaces, an anion permeable membrane disposed adjacent to one of said upper and lower surfaces and a cation permeable membrane disposed adjacent to the other of said upper and lower surfaces to thereby define a first compartment between said anion permeable and said cation permeable membranes, the periphery of the disk-shaped spacer having a process stream inlet and the central hub of the spacer including at least one transit channel isolated from the first compartment, the transit channel providing fluid communication at least with a second compartment positioned immediately adjacent to and isolated from said first compartment, the hub further including a process stream outlet constructed and arranged to provide fluid communication with at least one other compartment, said other compartment isolated from said first compartment and having at least one second compartment disposed between itself and the first compartment.