A modular dialysate regeneration assembly, comprising: a plurality of sorbent compartments each containing at least one sorbent material wherein the sorbent compartments are attachable to each other in a stack to form a modular dialysate regeneration assembly; and a processor configured to receive input patient and/or dialysis parameters and to generate a desired dialysate regeneration profile based on the input dialysis parameters and/or patient parameters, wherein the processor is configured to determine a number and/or the size of each sorbent compartment necessary in the stack to satisfy the dialysate regeneration profile based on the patient parameters and/or the dialysis parameters; and wherein at least one of the one or more sorbent compartments has a circular or rectangular planar base having a wall extending perpendicularly and upwardly from said base defining an internal area; and a circular or substantially rectangular planar top matching the planar base wherein the sorbent compartment has an engagement configuration selected from any one of (i) the base cooperatively engaging with the top of another sorbent compartment and the top cooperatively engaging with the base of another sorbent compartment; (ii) the base not cooperatively engaging with the top of another sorbent compartment and the top cooperatively engaging with the base of another sorbent compartment; and (iii) the base cooperatively engaging with the top of another sorbent compartment and the top not cooperatively engaging with the base of another sorbent compartement. a plurality of sorbent compartments each containing at least one sorbent material wherein the sorbent compartments are attachable to each other in a stack to form a modular dialysate regeneration assembly; and a processor configured to receive input patient and/or dialysis parameters and to generate a desired dialysate regeneration profile based on the input dialysis parameters and/or patient parameters, wherein the processor is configured to determine a number and/or the size of each sorbent compartment necessary in the stack to satisfy the dialysate regeneration profile based on the patient parameters and/or the dialysis parameters; and wherein at least one of the one or more sorbent compartments has a circular or rectangular planar base having a wall extending perpendicularly and upwardly from said base defining an internal area; and a circular or substantially rectangular planar top matching the planar base wherein the sorbent compartment has an engagement configuration selected from any one of (i) the base cooperatively engaging with the top of another sorbent compartment and the top cooperatively engaging with the base of another sorbent compartment; (ii) the base not cooperatively engaging with the top of another sorbent compartment and the top cooperatively engaging with the base of another sorbent compartment; and (iii) the base cooperatively engaging with the top of another sorbent compartment (i) the base cooperatively engaging with the top of another sorbent compartment and the top cooperatively engaging with the base of another sorbent compartment; (ii) the base not cooperatively engaging with the top of another sorbent compartment and the top cooperatively engaging with the base of another sorbent compartment; and (iii) the base cooperatively engaging with the top of another sorbent compartment and the top not cooperatively engaging with the base of another sorbent compartement. <EOS>