Electrodialysis reversal (EDR) is an

electrodialysis Electrodialysis (ED) is used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference. This is done in a configuration called an electrodialysis ...

reversal

water desalination Desalination is a process that removes mineral components from saline water. More generally, desalination is the removal of salts and minerals from a substance. One example is soil desalination. This is important for agriculture. It is possible ...

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

process that has been commercially used since the early 1960s. An

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

migrates dissolved

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s, including

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an Inorganic chemistry, inorganic, Monatomic ion, monatomic Ion#Anions and cations, anion of fluorine, with the chemical formula (also written ), whose ...

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

s and

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

s, through an electrodialysis stack consisting of alternating layers of

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

ic and

anionic An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

ion exchange Ion exchange is a reversible interchange of one species of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid. Ion exchange is used in softening or demineralizing of water, purification of ch ...

membranes. Periodically (3-4 times per hour), the direction of ion flow is reversed by reversing the polarity of the applied electric current. Current reversal reduces clogging of membranes, as salt deposits in the membrane gets dissolved when the current flow is reversed. Electrodialysis reversal causes a small decrease in the diluted feed quality and requires increased complexity infrastructures, as reversible valves are required to change the flow direction of diluted and concentrated streams. However, it greatly increases ion exchange membranes durability, and membrane cleaning prevents electrical resistance increase of membrane as deposits accumulate in the membrane pores. The polarity reversal of EDR alternately exposed membrane surfaces and the water flow paths to concentrate with a tendency to precipitate scale and desalted water that tends to dissolve scale. This allows the process to operate with supersaturated concentrate streams up to specific limits without chemical additions to prevent scale formation.

References

External links

Article: Water issues prompt new look at desalination
{{Webarchive, url=https://web.archive.org/web/20100308122034/http://americancityandcounty.com/mag/government_water_issues_prompt/ , date=2010-03-08 Water desalination Membrane technology

See also

References

External links