A system for infusing a buffer into a dialysate, comprising a dialysate flow loop (46) for circulating a dialysate through a dialyzer, wherein acid or base equivalents are added to the dialysate during operation of the dialysate flow loop； a dialysate regeneration unit comprising a sorbent cartridge comprising at least one sorbent material； at least one urea sensor (41) that measures or allows for the calculation of urea content of the dialysate in at least one portion of the dialysate flow loop； wherein the urea sensor measures the urea content of the dialysate directly, or measures the urea content of the dialysate indirectly by measuring changes in any one or more of conductivity, pH, CO2, or ammonia concentration； wherein at least one urea sensor is located downstream of the sorbent cartridge； an infusate system (43) configured to add a bicarbonate buffer component or unbuffered sodium bicarbonate to the dialysate； and a controller in communication with the urea sensor, the controller configured to calculate an amount of bicarbonate generated by the dialysate regeneration unit due to the urea content of the dialysate in the at least one portion of the dialysate flow loop, the controller controlling an amount of the bicarbonate buffer component or unbuffered sodium bicarbonate for addition to the dialysate to generate a predetermined total bicarbonate buffer concentration in the dialysate entering the dialyzer, based at least in part on the amount of bicarbonate generated by the dialysis regeneration unit.
