An apparatus and method for replenishing urease in a sorbent cartridge for use in sorbent dialysis. The sorbent cartridge is configured to allow an amount of urease to be added to the sorbent cartridge. A urease solution can be injected into the sorbent cartridge to replenish the urease containing module, or solid urease can be added to the sorbent cartridge. The sorbent module can also comprise other, rechargeable, sorbent materials for removing toxins other than urea from spent dialysate.