Editing Desalination (section)

==== Hydrogel based desalination ====
[[File:TOC new.png|thumb|upright=1.25|Scheme of the desalination machine: the desalination box of volume <math>V_{box}</math> contains a gel of volume <math>V_{gel}</math> which is separated by a sieve from the outer solution volume <math>V_{out} = V_{box} - V_{gel}</math>.  The box is connected to two big tanks with high and low salinity by two taps which can be opened and closed as desired.  The chain of buckets expresses the fresh water consumption followed by refilling the low-salinity reservoir by salt water.<ref name="RudBorisovKosovan2018">{{cite journal|title=Thermodynamic model for a reversible desalination cycle using weak polyelectrolyte hydrogels|journal=Desalination|volume=442|page=32|doi=10.1016/j.desal.2018.05.002 |ref=Rud2018|year=2018|last1=Rud|first1=Oleg|last2=Borisov|first2=Oleg|last3=Košovan|first3=Peter|bibcode=2018Desal.442...32R |s2cid=103725391}}</ref>]]
The idea of the method is in the fact that when the hydrogel is put into contact with aqueous salt solution, it swells absorbing a solution with the ion composition different from the original one. This solution can be easily squeezed out from the gel by means of sieve or microfiltration membrane. The compression of the gel in closed system lead to change in salt concentration, whereas the compression in open system, while the gel is exchanging ions with bulk, lead to the change in the number of ions. The consequence of the compression and swelling in open and closed system conditions mimics the reverse Carnot Cycle of refrigerator machine. The only difference is that instead of heat this cycle transfers salt ions from the bulk of low salinity to a bulk of high salinity. Similarly to the Carnot cycle this cycle is fully reversible, so can in principle work with an ideal thermodynamic efficiency. Because the method is free from the use of osmotic membranes it can compete with reverse osmosis method. In addition, unlike the reverse osmosis, the approach is not sensitive to the quality of feed water and its seasonal changes, and allows the production of water of any desired concentration.<ref name="RudBorisovKosovan2018"/>