Dialysis treatment devices for removing urea

1. A dialysis treatment device comprising:

a first filter comprising a filtration membrane, the first filter having a retentate stream;

a urea removal unit comprising urease and in fluid communication with the first filter;

a second filter comprising an ion rejection membrane and in fluid communication with the retentate stream of the first filter and the urea removal unit; and

a flow restrictor positioned between the first filter and the second filter.

2. The dialysis treatment device of claim 1 , wherein the filtration membrane is selected from the group consisting of: a nanofiltration membrane, a reverse osmosis membrane, an ion rejection membrane and combinations thereof.

3. The dialysis treatment device of claim 1 , wherein the filtration membrane of the first filter comprises a cation rejection membrane and the ion rejection membrane of the second filter comprises a cation rejection membrane.

4. The dialysis treatment device of claim 1 , wherein the dialysis treatment device is contained within a cartridge for a wearable kidney.

5. The dialysis treatment device of claim 1 further comprising a pump positioned between the urea removal unit and the first filter.

6. The dialysis treatment device of claim 1 , wherein a flow path between the urea removal unit and the second filter is sufficiently long enough to prevent the urease from being saturated with ammonia.

7. The dialysis treatment device of claim 1 further comprising an activated carbon unit in fluid communication with the first filter.

8. The dialysis treatment device of claim 1 wherein the ion rejection membrane is a reverse osmosis membrane.

9. The dialysis treatment device of claim 1 further comprising zirconium phosphate layer in fluid communication with the second filter.

10. A dialysis treatment device comprising:

a first filter comprising a filtration membrane that separates a waste fluid stream into a retentate stream and a filtrate stream comprising urea;

a urea removal unit comprising urease and in fluid communication with the first filter, the urea removal unit receiving the filtrate stream from the first filter and converting the urea from the filtrate stream into an ammonia stream;

a second filter comprising an ion rejection membrane and in fluid communication with the first filter and the urea removal unit, the second filter receiving at least one of the retentate stream from the first filter or the ammonia stream from the urea removal unit;

a flow restrictor positioned between the first filter and the second filter; and

an ammonia sorbent in fluid communication with the second filter.

11. The dialysis treatment device of claim 10 , wherein the filtration membrane is selected from the group consisting of: a nanofiltration membrane, an ion rejection membrane and combinations thereof.

12. The dialysis treatment device of claim 10 , wherein the filtration membrane of the first filter comprises a cation rejection membrane and the ion rejection membrane of the second filter comprises a cation rejection membrane.

13. The dialysis treatment device of claim 10 , wherein the dialysis treatment device is contained within a cartridge for a wearable kidney.

14. The dialysis treatment device of claim 10 further comprising a pump positioned between the urea removal unit and the first filter.

15. The dialysis treatment device of claim 10 , wherein a flow path between the urea removal unit and the second filter is sufficiently long enough to prevent the urease from being saturated with ammonia.

16. The dialysis treatment device of claim 10 further comprising an activated carbon unit in fluid communication with the first filter.

17. The dialysis treatment device of claim 10 wherein the ammonia sorbent comprises a zirconium phosphate layer.