A modular assembly system for a portable hemodialysis unit, comprising: a dialysis unit including a dialysis unit housing that contains components for performing hemodialysis, including a dialyzer mount with fluidic connections for a dialyzer, a blood pump mounting section with pneumatic connections for operation of one or more pneumatically driven blood pumps to circulate blood through a dialyzer when mounted in the dialysis unit housing, one or more pneumatically driven dialysate pumps to circulate a dialysate through the dialyzer, a dialysate heater, and one or more electronic controllers for controlling the one or more blood and dialysate pumps； and a pneumatic power unit within a pneumatic power unit housing configured to provide pneumatic power to the dialysis unit via mating pneumatic ports between the pneumatic power unit housing and the dialysis unit housing； wherein the pneumatic power unit housing is reversibly connectable to the dialysis unit housing via a mechanical and pneumatic connection to the dialysis unit.
