Apparatuses, systems, and methods for the performance of kidney replacement therapy having or using a dialyzer, control components, sorbent cartridge, and fluid reservoirs configured to be of a weight and size suitable to be worn or carried by an individual requiring treatment are disclosed. The system has a controlled compliance dialysis circuit, where a control pump controls the bi-directional movement of fluid across a dialysis membrane. A first sorbent cartridge is provided for use in a portable treatment module having activated carbon and zirconium oxide. The system also provides for the monitoring of an inlet and outlet conductivity of a sorbent cartridge containing urease to provide a facility to quantify or monitor the removal of urea by a detachable urea removal module.
